Windows Server 2019 Retirement on AKS enabled by Azure Arc
Action Required: Migrate to Windows Server 2022 by April 2026 As previously announced, Microsoft is retiring Windows Server 2019 support on Azure Kubernetes Service (AKS) enabled by Azure Arc (formerly AKS Hybrid on Azure Local releases after April 1, 2026. If you're running Windows Server 2019 workloads, you must migrate to Windows Server 2022 to maintain support, security updates, and the ability to upgrade Kubernetes versions. Migration Approach You cannot upgrade Windows node pools in place. The migration process requires: Creating new Windows Server 2022 node pools Updating and rebuilding container images with WS2022 base images Migrating workloads to the new pools Decommissioning old Windows Server 2019 pools Make sure to allocate 2-4 weeks for testing, and plan to complete production migration by March 2026. Key Milestones Milestone Date Details Windows Server 2019 Support Ends Post April 1, 2026 No support or security updates after this date Windows Server 2019 Retirement Post April 1, 2026 In new releases cannot create new node pools with WS2019 Default Image Changes to WS2022 Early 2026 New deployments default to Windows Server 2022 Why Is This Happening? End of Mainstream Support: Windows Server 2019 mainstream support ended on January 9, 2024. Simplified Experience: Starting early 2026, Windows Server 2022 will be the default OS SKU, providing a seamless experience for new deployments. What Happens After Retirement? Immediate Impact on Your Clusters Starting April 1, 2026, clusters still running Windows Server 2019 node pools will face the following restrictions: Kubernetes Upgrade Blocking: Attempting to upgrade to Kubernetes versions (with Windows Server 2019 node pools) will be blocked Error message: "Windows Server 2019 images not available for the selected Kubernetes version. Please re-create your Windows node pool with a supported OS SKU" Node Pool Creation Restrictions: Cannot create new Windows node pools with Windows Server 2019 OS SKU Loss of Support: Support cases opened for clusters with Windows Server 2019 will require upgrade before assistance No security patches or updates will be available Clusters will be considered out of compliance Default Image Transition (Early 2026) Starting in early 2026, Windows Server 2022 will become the default OS SKU for all new Windows node pool deployments created on the clusters on the latest Azure Local releases. This change ensures new deployments automatically use the supported OS version, reducing the risk of accidentally deploying deprecated images. Getting Started For detailed step-by-step instructions, see our Migration How-to Guide, which includes: Commands to identify affected clusters Container image update procedures Node pool creation and workload migration steps Validation and troubleshooting guidance Frequently Asked Questions General Questions Q: What happens if I don't upgrade before the retirement date? A: After April 2026, your clusters running Windows Server 2019 will lose support. You will be required to upgrade before receiving any assistance from Microsoft support. Your clusters will also be unable to upgrade to Kubernetes versions, potentially leaving them on unsupported Kubernetes releases. Q: Can I upgrade my Windows node pools in place? A: No. Windows node pools cannot be upgraded in place. You must create new node pools with Windows Server 2022, migrate your workloads, and then decommission the old node pools. Q: Will my existing container images work on Windows Server 2022? A: Most Windows Server 2019 container images will work on Windows Server 2022 hosts. However, we recommend rebuilding your images on the Windows Server 2022 base for optimal performance, security, and compatibility. Q: Can I upgrade my Kubernetes version with Windows Server 2019 node pools still running? A: No. Upgrades to Kubernetes versions will be blocked if you have any Windows Server 2019 node pools in your cluster. You must migrate to Windows Server 2022 first. Migration Questions Q: How long does a typical migration take? A: Migration time varies based on the number of applications, complexity, and data volume. Simple applications may migrate in hours, while complex environments may take days or weeks. Plan for adequate testing time. Q: Can I run Windows Server 2019 and Windows Server 2022 node pools in the same cluster? A: Yes, during the migration period you can have node pools with different OS SKUs in the same cluster. This enables gradual migration and testing. Q: Will there be any downtime during migration? A: Downtime depends on your migration strategy. For stateless applications using rolling updates, downtime can be minimal or zero. Stateful applications may require planned maintenance windows. Additional Resources: AKS enabled by Azure Arc Overview Windows Container Upgrade Guide Original Retirement AnnouncementDesigning for High Availability: The Operational Reference for Running a Geo-Replicated ACR
By Johnson Shi, Zoey (Zhuyu) Li, Huangli Wu Introduction Three of the most common questions we hear from enterprise teams running geo-replicated Azure Container Registries (ACR) are: "How do I control which region serves my traffic?" — When my AKS clusters are spread across regions, can I pin each one to its co-located replica, or am I stuck with however the global endpoint routes? "What happens during a regional incident — is failover automatic or do I have to act?" — If the registry in one region degrades, does the global endpoint reroute on its own, or do I need to manually disable the affected replica? "What happens after the region recovers — does traffic return on its own?" — Is there a cooldown, a quarantine, or any manual step before failback? We answer those head-on, then go deeper on the operational details that come up when you actually run a geo-replicated registry: authentication across endpoint switches, throttling under load concentration, eventual-consistency failure modes, home region outage scope, webhooks, and private endpoint interaction. We draw on the official geo-replication docs, the global endpoint health-aware failover blog, the regional endpoints engineering design implementation, the regional endpoints public preview and private preview announcements, and the ACR reference for various registry endpoints, . This post also draws notes from the ACR product team on roadmap items that aren't yet documented elsewhere. Key Takeaways Health-aware failover is automatic. When the registry in a region degrades, the global endpoint reroutes away from it on the order of minutes, evaluated per-registry. No customer action required. Failback is automatic too. Once health-aware failover marks a region healthy again, the global endpoint resumes routing to it. There is no cooldown period. Health-aware failover applies only to global endpoint operations. It does not apply to regional endpoints (you're talking to one replica, period) or to dedicated data endpoints (the redirect is per-region). Health-aware failover is not triggered by throttling. It responds to regional ACR service health and Azure infrastructure health, not HTTP 429 responses. Use regional endpoints to manage per-replica throttling. Regional endpoints (Step 2a) give you explicit per-region URLs for workloads that need affinity, capacity planning, push/pull consistency, troubleshooting, or client-side failover. Use myregistry.<region>.geo.azurecr.io . Regional endpoints are available on Premium SKU registries. For workloads that don't need pinning, do nothing (Step 2b). The global endpoint plus health-aware failover handles routing automatically. Re-authenticate when switching endpoints. Each global or regional endpoint is its own authenticated surface; re-auth via az acr login , SDK auth, or the Kubernetes ACR credential provider on endpoint change. Don't run a long-lived DNS cache for the global endpoint. ACR purges DNS server-side on disable and during failover; a long-lived client cache works against that. For production workloads, enable dedicated data endpoints for security and DNS predictability on layer downloads. ACR is working on bounded staleness consistency for cross-replica eventual-consistency failure modes; see the FAQ. Background What is ACR geo-replication? Geo-replication is a Premium SKU feature that turns a single ACR registry into a multi-region, multi-write service. Every geo-replica in every region is writable — you can push, pull, and delete from any of them — and content syncs asynchronously between replicas under an eventual consistency model. Per-push replication time scales with the size and number of images being pushed. Similarly, when creating a new geo-replica, the time to populate the new geo-replica scales with the total size of the registry. A geo-replicated registry exposes a global endpoint at myregistry.azurecr.io . Behind that endpoint, ACR uses an internal traffic manager to direct each request to the replica with the best network performance profile for the caller — usually the closest replica, but not always. When clients are equidistant from multiple replicas, or when the closest replica is experiencing Azure infrastructure degradation, requests may be routed elsewhere. A geo-replicated registry also exposes a regional endpoint at myregistry.<region>.geo.azurecr.io , which allows clients to pin API requests to a specific geo-replica in lieu of global endpoints, which has Azure-managed routing among geo-replicas. Zone redundancy is always enabled for geo-replicas in regions where Azure has multiple availability zones — in those regions, ACR automatically spreads replica data across multiple availability zones within each region to protect against zonal outages. Endpoints and data endpoints: what goes where A common point of confusion: when you push or pull, not every request goes to the same place. The registry endpoints (global endpoint and regional endpoints), as well as the data endpoint, do different jobs. Your choice of data endpoint configuration has real consequences for security and resilience. Two kinds of traffic flow during a typical pull: Registry API traffic — authentication, manifest reads/writes, tag resolution, referrers, repository operations, blob location lookups, listing, metadata. This is everything except the actual layer (blob) bytes. All these API requests go to the global endpoint ( myregistry.azurecr.io ) or, if you've pinned your clients to call these APIs to a specific geo-replica, a geo-replica's regional endpoint ( myregistry.<region>.geo.azurecr.io ). Behind the scenes, the global endpoint internally proxies these requests to a specific geo-replica. Layer (blob) downloads — when the client asks for a blob, the registry doesn't serve the bytes itself. It returns an HTTP 307 redirect to a regional data endpoint (separate endpoint from the global endpoint or regional endpoints), and the client follows the redirect to download the layer from that region. Where that 307 sends you depends on whether you've enabled the registry's dedicated data endpoints feature: Configuration Layer downloads redirect to Default (no dedicated data endpoints) *.blob.core.windows.net (the underlying Azure storage account) Dedicated data endpoints enabled myregistry.<region>.data.azurecr.io for the region you were routed to Private endpoints enabled myregistry.<region>.data.azurecr.io for the region you were routed to Regional by design. Dedicated data endpoints always land you on a specific geo-replica's data endpoint — there is no "global data endpoint." With the global endpoint as your registry endpoint, the 307 redirect picks the data endpoint for whichever region the global endpoint chose to serve you. With a regional endpoint pinned to a specific region, the 307 always redirects you to that same region's data endpoint — never cross-region. Why dedicated data endpoints matter. Dedicated data endpoints are a Premium SKU feature that exists primarily to address security and firewall scoping. By default, layer downloads redirect to *.blob.core.windows.net — a wildcard storage FQDN. Firewall rules to allow that wildcard either let all Azure storage accounts through or none of them, which raises data exfiltration concerns and isn't tightly scoped to your registry. Dedicated data endpoints replace the wildcard with a fully qualified domain in your registry's own domain — myregistry.<region>.data.azurecr.io — so firewall rules can be scoped tightly to your specific registry, in your specific regions. That same design choice can also make layer downloads more predictable during routing changes. With dedicated data endpoints, the data endpoint FQDN is known ahead of time and lives in the registry's domain — one predictable hostname per region, configured once. Without them, the layer download has to resolve a wildcard storage FQDN that points to whichever storage account the registry happens to have provisioned, which is a separate DNS resolution path with its own routing behavior and its own caching profile. Dedicated data endpoints simplify the DNS picture by aligning the data path with the registry path and keeping the entire pull experience inside one set of predictable, scoped FQDNs. For any geo-replicated registry where security and high availability matter, enable dedicated data endpoints. Note: Health-aware failover applies only to operations against the global endpoint, not to regional endpoints or dedicated data endpoints. Take note that health-aware failover only kicks in and directs traffic away from a geo-replica when an Azure region is experiencing significant infrastructure degradation. At this stage, it does not kick in to redirect traffic to another geo-replica if a client's data plane API requests are throttled. See the relevant section below for the full scope when health-aware auto failover kicks in or not. The three traffic control tools ACR geo-replication gives you three complementary tools for controlling where traffic lands. Each one solves a different class of problem, and customers most often run into trouble when they reach for the wrong one. We name them up front and use these names throughout the post: Tool Who controls it What it does Use cases Health-aware failover Platform (automatic) Reroutes the global endpoint away from a region whose registry can't reliably serve requests Regional incidents, automatic recovery Replica enable/disable for global routing Customer (manual) Excludes a specific replica from global endpoint routing without deleting it; data continues syncing DR rehearsals, planned maintenance, quarantining a replica without losing it Regional endpoints Customer (per request) Dedicated per-region URLs ( myregistry.<region>.geo.azurecr.io ) that bypass the internal traffic manager entirely Pinning AKS clusters to co-located replicas, push/pull consistency, capacity planning, troubleshooting, client-side failover Health-aware failover and replica enable/disable both act on the global endpoint. Regional endpoints are a separate URL surface that coexists with the global endpoint — enabling them does not disable the global endpoint myregistry.azurecr.io . You can use both simultaneously and choose per workload. The behavior in question When the registry in one region experiences a real degradation, there are three possible answers to "what happens?": (A) Nothing automatic. The customer must manually disable the affected region's endpoint to stop traffic from being routed there. (B) The system detects the regional front-door failure and reroutes within seconds. (C) A per-registry health evaluation detects the degradation and reroutes the global endpoint within minutes, with no customer action. After the region recovers, routing resumes automatically. The answer today is (C). Before health-aware failover, customers were stuck closer to (A) — the system could see whether the regional reverse proxy responded, but not whether the registry could actually serve real pull and push traffic end to end. Health-aware failover closes that gap. We walk through all three tools in the next section, in order: setting up geo-replication, using regional endpoints to pin specific workloads, keeping the global endpoint for everything else, the manual replica disable mechanism, re-enabling participation in global routing, and what to expect when health-aware failover triggers. Walkthrough The following steps assume an existing Premium SKU registry and the Azure CLI logged in. We use myregistry as the registry name, myrg as the resource group, and eastus as the home region. Substitute <your-registry> , <your-rg> , and <your-region> for your environment. Prerequisites A Premium SKU ACR registry (geo-replication requires Premium) Azure CLI ( az ) installed and logged in For regional endpoints (Step 2a): Azure CLI 2.86.0 or later. All regional endpoints commands ( --regional-endpoints , az acr show-endpoints , az acr login --endpoint ) are available natively in Azure CLI 2.86.0+. If you previously installed the acrregionalendpoint private preview CLI extension, uninstall it with az extension remove --name acrregionalendpoint to prevent conflicts with the built-in CLI commands. Step 1: Add a West US replica to a registry that lives in East US Geo-replication requires the Premium SKU. The create call below fails on Basic or Standard. # Confirm the registry is Premium az acr show --name myregistry --resource-group myrg \ --query sku.name --output tsv # Premium # Create a West US geo-replica az acr replication create --registry myregistry --location westus # Confirm both replicas are present az acr replication list --registry myregistry --output table NAME LOCATION PROVISIONING STATE STATUS REGION ENDPOINT ENABLED ------ ---------- -------------------- -------- ----------------------- eastus eastus Succeeded online True westus westus Succeeded online True Pushes and pulls continue working through the existing replica throughout initial sync. Because the registry is multi-region, multi-write, the existing replica keeps serving traffic while the new replica catches up in the background. Initial replica seeding time is a function of registry size — the total number and cumulative size of images already in the registry that need to be replicated to the new replica — not the size of any single image. Step 2a: Pin workloads to specific regions using regional endpoints Use regional endpoints when a workload needs explicit per-region control. The five common cases: Regional affinity — an AKS cluster in East US should pull from the East US replica, every time, without ever hopping to a more distant replica because of a network performance fluctuation. Predictable routing — workloads that need to know exactly which replica will serve them, for benchmarking, capacity planning, or in-region traffic SLAs. Push/pull consistency — pinning both ends of a publish-then-deploy flow to the same replica eliminates eventual-consistency races. Troubleshooting — reproducing an issue on a specific replica requires sending traffic to that specific replica. Client-side failover — customers with their own health checks and business rules want to implement failover on their own terms, on signals only they can see. Enable regional endpoints on the registry: az acr update -n myregistry -g myrg --regional-endpoints enabled When enabled, ACR automatically creates per-region login server URLs for every existing geo-replica. No per-region configuration is needed. Note: Regional endpoints can be enabled on any Premium SKU registry, even without geo-replication. A registry without geo-replication has a single geo-replica in the home region, which gets one regional endpoint URL. However, the feature is most useful when your registry has at least two geo-replicas, where you can pin different workloads to different replicas for routing control and capacity distribution. Push to a specific region using its regional endpoint: # Log in to the West US regional endpoint az acr login --name myregistry --endpoint westus # Tag and push using the regional endpoint URL docker tag myapp:v1 myregistry.westus.geo.azurecr.io/myapp:v1 docker push myregistry.westus.geo.azurecr.io/myapp:v1 Pin AKS deployments to their co-located replica by using regional endpoint URLs in the deployment manifest. The example below shows two clusters in different regions; each cluster references the regional endpoint for its own region's replica (assuming replicas exist in both eastus and westeurope ): # East US-based AKS cluster pulls from the East US replica apiVersion: apps/v1 kind: Deployment metadata: name: myapp-eastus spec: template: spec: containers: - name: myapp image: myregistry.eastus.geo.azurecr.io/myapp:v1 --- # West Europe-based AKS cluster pulls from the West Europe replica apiVersion: apps/v1 kind: Deployment metadata: name: myapp-westeurope spec: template: spec: containers: - name: myapp image: myregistry.westeurope.geo.azurecr.io/myapp:v1 This eliminates cross-region pulls when global routing would otherwise prefer a different replica for a given client, and it gives you a per-region traffic profile you can plan capacity against. Regional endpoint operational tips View all endpoints. Use az acr show-endpoints to see all endpoint URLs for your registry — global, regional (if enabled), and dedicated data endpoints (if enabled): az acr show-endpoints --name myregistry --resource-group myrg Import from a specific geo-replica. When importing images between registries, you can use a regional endpoint to import from a specific geo-replica of the source registry. This is useful when you want predictable network paths or need to import from a replica in a specific region: az acr import \ --name mydownstreamregistry \ --source myupstreamregistry.westeurope.geo.azurecr.io/myapp:v1 \ --image myapp:v1 Firewall rules for regional endpoints. If you use firewall rules, allow access to the following endpoints for each geo-replica that clients connect to: Endpoint Purpose myregistry.<region>.geo.azurecr.io Regional endpoint for registry operations myregistry.azurecr.io Global endpoint (if also used) myregistry.<region>.data.azurecr.io Layer downloads (if using private endpoints or dedicated data endpoints) *.blob.core.windows.net Layer downloads (if not using private endpoints or dedicated data endpoints) For the full list of endpoint types and FQDN patterns, see the ACR reference for various registry endpoints. DNS-based routing without changing manifests. If you don't want to maintain different deployment manifests per region, you can keep all manifests pointing to the global endpoint ( myregistry.azurecr.io ) and use software-defined networking or a regional traffic manager to resolve the global endpoint to the appropriate regional endpoint based on the originating region's traffic. This achieves the same co-location goals as regional endpoints — predictable routing and reduced latency — without embedding region-specific URLs in your deployment manifests. Step 2b: Keep using the global endpoint for everything else For workloads that don't need explicit pinning, do nothing. The global endpoint at myregistry.azurecr.io continues to work exactly as before, and the global endpoint plus health-aware failover gives you intelligent routing across replicas without configuration. ACR picks the best replica for each client based on network performance and reroutes during regional incidents. Regional endpoints coexist with the global endpoint — enabling them does not disable myregistry.azurecr.io . You can use both simultaneously and choose per workload, mixing pinned workloads (Step 2a) with workloads that ride the global endpoint (Step 2b) in the same registry. Step 3: Take a replica out of global endpoint routing Use this when you need to keep a replica alive but stop it from serving global-endpoint traffic — for DR rehearsals, planned maintenance, or troubleshooting an isolated replica. # Exclude the West US replica from global endpoint routing az acr replication update --registry myregistry --name westus \ --global-endpoint-routing false Confirm the change: az acr replication list --registry myregistry --output table NAME LOCATION PROVISIONING STATE STATUS REGION ENDPOINT ENABLED ------ ---------- -------------------- -------- ----------------------- eastus eastus Succeeded online True westus westus Succeeded online False Requests to myregistry.azurecr.io no longer route to West US. The replica still receives replicated content — and continues to replicate its own content out to other replicas — and storage quota and per-replica costs continue to accrue. If regional endpoints are enabled, the West US regional endpoint URL also continues to work; --global-endpoint-routing controls only the replica's participation in global endpoint routing. A note on naming. The CLI flag --global-endpoint-routing (on az acr replication update ) and the regional endpoints feature (enabled via az acr update --regional-endpoints enabled ) are two different things despite the similar names. --global-endpoint-routing controls whether a replica participates in global endpoint routing. The regional endpoints feature creates per-region URLs ( myregistry.<region>.geo.azurecr.io ) that bypass the global endpoint entirely. They are independent controls. In Azure CLI 2.86.0 and later, the old --region-endpoint-enabled flag has been renamed to --global-endpoint-routing . The old flag name is deprecated and will be removed in Azure CLI 2.87.0 (June 2026). If you have existing scripts or automation that use --region-endpoint-enabled , update them to use --global-endpoint-routing . CLI flags quick reference: Flag Scope Purpose --regional-endpoints Registry-level ( az acr create or az acr update ) Enables dedicated regional endpoint URLs ( myregistry.<region>.geo.azurecr.io ) for all geo-replicas. --global-endpoint-routing Per-geo-replica ( az acr replication create or az acr replication update ) Controls whether the global endpoint routes traffic to a specific geo-replica. Set to false to temporarily exclude a geo-replica from global routing. --data-endpoint-enabled Registry-level ( az acr create or az acr update ) Enables dedicated data endpoints ( myregistry.<region>.data.azurecr.io ) for layer blob downloads. Auto-enabled when at least one private endpoint is configured. This bidirectional sync during disable is intentional. When you re-enable the replica, every image pushed to the registry while the replica was disabled — from any region — is already present, so the replica can serve traffic immediately with no catch-up window. If we stopped syncing on disable, re-enabling would leave the replica with stale data and force a long catch-up before it could safely serve pulls. Step 4: Re-enable the replica to participate in global endpoint routing Re-enable the replica: az acr replication update --registry myregistry --name westus \ --global-endpoint-routing true NAME LOCATION PROVISIONING STATE STATUS REGION ENDPOINT ENABLED ------ ---------- -------------------- -------- ----------------------- eastus eastus Succeeded online True westus westus Succeeded online True There is no cooldown. The global endpoint resumes routing requests to the West US replica as soon as the change takes effect on ACR's side. Because data continued syncing while the replica was disabled (Step 3), the replica is immediately ready to serve pulls — no catch-up window. Note on DNS during disable/enable. When you take a replica out of global routing, ACR purges its own DNS records for that replica from the global endpoint on a fast path — there is no waiting on a published TTL on ACR's side. If clients run their own DNS cache for the global endpoint, however, those clients will keep resolving to the disabled replica until the client cache expires. We can't control client-side caches. The recommendation: do not run a long-lived DNS cache for the global endpoint. A short-lived DNS pin for the duration of a single push (covered in the DNS and Client-Side Considerations section) is fine and even helpful — but a long-lived DNS cache will make --global-endpoint-routing false look broken from the client's perspective. Step 5: What to expect when health-aware failover triggers Health-aware failover is automatic. ACR evaluates registry health on a per-registry basis, and when a registry in a region can't reliably serve requests, the global endpoint reroutes that registry's traffic to a healthy replica. There is no customer-invocable trigger — that's the point. End-to-end timing is on the order of minutes — fast enough to catch real regional degradation, slow enough to ride out transient errors that resolve on their own. DNS TTL may add additional propagation delay before all clients switch to the new region. Scope of health-aware failover. Health-aware failover applies only to operations against the global endpoint — the registry API calls (auth, get manifest, get tag, get referrers, get blob location). It evaluates health when those API calls come in; it does not trigger mid-operation. Two important consequences: Regional endpoints are not in scope. When you talk to a regional endpoint like myregistry.westus.geo.azurecr.io , you're talking to that one replica. There is no automatic reroute. If you've pinned a workload to a regional endpoint and that region degrades, you implement client-side failover by switching the workload to a different regional endpoint. Dedicated data endpoints are not in scope. Once a registry endpoint has redirected you to a dedicated data endpoint, you stay on that region's data endpoint for the duration of the layer download. There is no automatic reroute of an in-flight blob download. The region targeted by the redirect is decided up front by whichever registry endpoint served the blob-location call: the global endpoint chooses based on its per-registry health evaluation, and a regional endpoint always targets its own region. The signals you can use to confirm a failover is in progress: # Check replication status az acr replication list --registry myregistry --output table You can also check Resource Health for the registry in the Azure portal — navigate to your registry and select Resource health under the Help section to see platform-side degradation signals. You'll typically see: Increased pull latency as traffic shifts to a more distant replica Resource Health flagging known issues in the affected region Replication status indicating which replicas are online After the region recovers, the per-registry health evaluation marks it healthy again and the global endpoint resumes routing — automatic, no cooldown, no customer action. Note that health is evaluated per registry, not per region: if a degradation affects only a subset of registries in a region, only those registries are rerouted, and other registries in the same region continue to be served locally with no unnecessary latency penalty. Not triggered by throttling. Health-aware failover is DNS-based and responds to regional ACR service health and Azure infrastructure health. It does not reroute traffic based on HTTP 429 (throttling) responses. If a geo-replica is throttling your requests but the region's infrastructure is healthy, the global endpoint continues routing you to that geo-replica. To manage throttling, use regional endpoints to spread workloads across multiple geo-replicas for better capacity distribution. Note on long-running pushes during a failover. A multi-layer push that spans a failover boundary can land layers and the manifest on different replicas — exactly the failure mode that DNS bouncing produces during a single push. ACR is actively tightening health-aware failover behavior to minimize cross-replica scatter during these scenarios, and the recommendation today remains: pin pushes to a single replica via a regional endpoint when push/pull consistency matters. Common Questions Q1. Performance impact during initial replica creation on a live registry Because ACR is multi-region, multi-write, the existing replica continues serving pull and push traffic throughout the period when a new replica is being seeded. Replication is asynchronous and content propagates in the background; the time to populate a new geo-replica scales with the size of the registry — the cumulative number and total size of images already in the registry — not with any single image. The docs do not publish a quantified degradation percentage or a throttling window for this period, and they do not promise zero performance impact — the safe operating assumption for a live production registry is that existing replicas continue serving traffic normally, with the new replica catching up in the background. Q2. Restricted/updating state during initial sync There is no "restricted" state for the registry during normal replica creation. Writes, control-plane operations, and pushes/pulls against existing replicas continue normally. The only time configuration changes are unavailable is during a home region outage — see the relevant FAQ item later on for the full data-plane-versus-control-plane breakdown. Q3. Cooldown periods and non-straightforward failback scenarios There is no cooldown before failback, manual or automatic. Re-enabling a replica's participation in global endpoint routing takes effect immediately on ACR's side. Health-aware failover returns traffic to a region as soon as its per-registry health evaluation passes again. The failback case that is not seamless: if a recently pushed image has not yet replicated to the failover region, a pull from that region may not find the image until replication catches up. This is a function of eventual consistency, not failback timing — and it's part of a broader class of issues we cover in Q4. Q4. Common pull and push failure modes during the eventual-consistency window DNS bouncing during a single push is one well-known problem, but it isn't the only one. The eventual-consistency window between geo-replicas surfaces in several recurring failure modes worth knowing about: Push-then-immediate-pull-cross-region. Pushing myapp:v1 to one region and immediately pulling it from a different region can fail with manifest unknown until replication catches up. This shows up most painfully in CI/CD pipelines where one CI runner pushes an image and thousands of pods across other regions all try to pull from their local geo-replicas at the same time. Today, customers work around this with indeterminate sleeps before scheduling expensive compute, or with retry logic, or by waiting on a replication-complete signal — none of which is a clean planning story. Tag overwrite races. Pushing myapp:v1 , then re-pushing myapp:v1 shortly after with a fix (same tag, different digest), can leave different replicas resolving the same tag to different digests during the eventual-consistency window. Delete propagation. Deleting a tag or repository in one region takes some time to propagate to other replicas. Pulls from regions where the delete hasn't yet propagated can return the supposedly-deleted content. Mid-push failover scatter. A multi-layer push that spans a health-aware failover boundary or a DNS bouncing event can land layers on one replica and the manifest on another, surfacing as manifest validation errors or blob unknown on subsequent pulls. What ACR is doing about this. We're working on bounded staleness consistency for pushed images across all geo-replicas worldwide, which addresses these four failure modes directly. This will be covered in an upcoming blog post. If you're hitting eventual-consistency brittleness today and want to talk through your scenario, reach out to us on the Azure Container Registry GitHub repository — we want the customer signal to land in the design. Mitigations available today: Pin pushes to a single replica via a regional endpoint. Every sub-request in the push — login, blob uploads, manifest upload — goes to the same replica, eliminating the DNS bouncing and mid-push scatter classes entirely. Use a short-lived client-side DNS cache like dnsmasq scoped to the duration of a single push, only when you're not using regional endpoints. Do not run a long-lived DNS cache for the global endpoint — it interferes with --global-endpoint-routing false and with health-aware failover routing. Build retry logic into pulls that immediately follow a cross-region push. Either retry with backoff or check replication status with ACR webhooks before pulling. ACR can detect and notify you when an image or tag is available for pull in a geo-replica (say geo-replica B), after it has been pushed to another geo-replica (geo-replica A) and background replication has succeeded to geo-replica B. Design publish steps to be idempotent so retries triggered by mid-push failover are safe. Q5. Auth behavior across endpoint switches For safety, treat each global endpoint and each regional endpoint as its own authenticated surface. All registry APIs except the actual blob downloads (auth, manifests, tag resolution, referrers) flow through whichever endpoint you've chosen. If you switch from the global endpoint to a regional endpoint, or from one regional endpoint to another, re-authenticate. That means az acr login , fresh SDK auth, or — for AKS — letting the Kubernetes ACR credential provider handle re-auth, which it does automatically when the endpoint changes. Q6. Throttling under failover and pinning Throttling limits on registry API operations are per-replica, not per-registry. This has two operational implications: During health-aware failover, traffic that was spread across replicas can shift heavily onto whichever replicas remain in the global endpoint's routing pool. Capacity plan to spread traffic across two or three healthy replicas during a failover scenario rather than concentrating onto one — the global endpoint's routing already does this for you when multiple healthy replicas exist, but registries with only two regions configured can hit per-replica limits more easily during a failover. To mitigate, use regional endpoints to spread workloads across multiple geo-replicas and plan per-replica capacity. When pinning via regional endpoints (Step 2a), you concentrate traffic on whichever replica you've pinned to. If you've pinned all your AKS clusters to a single regional endpoint, you may hit that replica's per-region throttling limits at peak. Mitigations: pin different workloads to different regional endpoints across multiple regions for better topology mapping and capacity distribution, or use the global endpoint (Step 2b) for workloads where you don't need explicit pinning so ACR's routing can spread load. We're also working on improving the throttling metrics surfaced during health-aware failover events. Note: Health-aware failover does not reroute traffic based on HTTP 429 (throttling). If you're experiencing throttling but the region's infrastructure is healthy, the global endpoint continues routing you there. Use regional endpoints to explicitly spread load across replicas for capacity planning. Q7. Home region outage scope Geo-replication provides high availability for the data plane. During a home region outage, the control plane is unavailable, which means you can't create or delete replicas, modify network rules, or change replication settings until the home region recovers. ACR Tasks are also bound to the home region and don't run while it's unavailable. The data plane keeps working: Global endpoint continues routing pulls and pushes to healthy replicas. Regional endpoints continue working — you talk directly to specific replicas, and your client-side logic decides which region to use. Authentication, manifests, blob downloads, webhooks continue functioning through any healthy replica. The home region of a registry is fixed at creation and cannot be changed afterward. Microsoft's registry relocation guidance describes a redeployment procedure — creating a new registry in a different region — not an in-place change to an existing registry's home region. Note: If your registry uses a customer-managed key, review the key vault failover and redundancy guidance for maximum resilience. Key vault availability directly affects the registry's ability to encrypt and decrypt data. Q8. Webhooks during failover Webhooks fire from the replica that received the push. Because ACR also replicates content to other geo-replicas, webhooks fire from each geo-replica as the image syncs to it — so a single push results in webhook events from the receiving replica plus an event from each replica as replication completes. During a failover where pushes are routed to a different region, webhooks from those pushes fire from the new region; once the original region recovers and replication catches up, webhook events fire from there too. Webhook consumers should be designed to handle multiple events per pushed image and deduplicate as needed. Q9. Private endpoints with regional endpoints and dedicated data endpoints When a private endpoint is created against a registry, the private endpoint covers all of the registry's endpoint surfaces — the global endpoint, every regional endpoint (if regional endpoints are enabled), and every regional dedicated data endpoint. A single private endpoint in one VNet can reach the global endpoint (which routes you to a suitable replica), any regional endpoint in the same or a different region, and any region's dedicated data endpoint for blob downloads. The trade-off is private IP allocation: each endpoint surface consumes IPs in the VNet. With many replicas plus regional endpoints plus dedicated data endpoints all enabled, private endpoint creation can fail if the VNet runs out of available private IPs. IP address consumption per feature: Configuration IPs consumed per VNet Initial private endpoint (global endpoint + home region dedicated data endpoint) 2 Each geo-replication region added +1 (regional dedicated data endpoint) Regional endpoints enabled +1 per geo-replica Example: A registry with 3 geo-replicas and regional endpoints enabled consumes 7 private IPs per VNet: 1 (global) + 3 (data) + 3 (regional). Without regional endpoints, the same registry requires 4 private IPs: 1 (global) + 3 (data). Subnet sizing: Use at minimum a /27 (32 addresses) subnet for PE subnets on geo-replicated registries, and /24 where possible. To check how many private IPs are already consumed on a subnet: az network vnet subnet show \ --name <subnet-name> \ --vnet-name <vnet-name> \ --resource-group <resource-group> \ --query "{addressPrefix:addressPrefix, usedIPs:length(ipConfigurations || \`[]\`)}" \ --output table See the ACR private endpoints documentation for the full IP-allocation math and sizing guidance. Q10. Geo-replica creation stuck for private endpoint-enabled registries When creating a geo-replica for a registry that has private endpoints configured, the replica provisioning can get stuck in a Creating state if the identity performing the operation doesn't have sufficient permissions to create private endpoint networking resources. Solution: Manually delete the geo-replica that got stuck in the provisioning state. Ensure the identity has the permission Microsoft.Network/privateEndpoints/privateLinkServiceProxies/write before creating the geo-replica again. Also verify that every PE subnet connected to the registry has free IP capacity — if any PE subnet across any connected VNet does not have enough free IPs, the replication provisioning fails and rolls back. The replica appears briefly in a Creating state and then is removed. The resulting error does not identify which subnet or VNet is exhausted. Q11. Metrics, logs, and alerts for the three phases We map each phase to the signals available in the Monitoring Guidance section below. The headline: Resource Health (in the Azure portal) and az acr replication list give you the platform-side signals; Azure Monitor platform metrics are collected automatically, and resource logs require Diagnostic Settings to be enabled on the customer side. Behavior summary Scenario Automatic? Customer Action Required Notes Registry in a region degrades Yes None Health-aware failover; per-registry; minutes-scale; global endpoint operations only Region recovers after a degradation event Yes None No cooldown Pin AKS clusters to co-located replicas No Use regional endpoint URLs in deployment manifests (Step 2a) Coexists with global endpoint No pinning needed for most workloads Yes None — keep using myregistry.azurecr.io (Step 2b) Global endpoint plus health-aware failover Push/pull from the same replica (consistency) No Use a regional endpoint for both push and pull Eliminates DNS bouncing and mid-push scatter Capacity planning per region No Spread workloads across multiple regional endpoints Per-replica throttling; avoid concentrating on one replica DR rehearsal: take a replica out of global routing No az acr replication update --global-endpoint-routing false Data continues syncing both directions; costs continue accruing Re-enable replica participation in global routing No az acr replication update --global-endpoint-routing true No cooldown; replica is immediately ready Switch a workload between endpoints No Re-auth ( az acr login , SDK auth, or Kubernetes ACR credential provider) Each endpoint is its own authenticated surface Initial replica seeding on a live registry N/A None Existing replica continues serving traffic; seeding time scales with registry size Long-running push during a failover No Retry; design publishes to be idempotent Pin via regional endpoint to avoid mid-push scatter; ACR is tightening this behavior Pull of a recently pushed image from a different region No Wait for replication, retry with backoff, or check replication status Eventual consistency; bounded staleness consistency in development Home region outage Data plane: yes; control plane: no Use global or regional endpoints for data plane operations Control plane (replica config, network rules) requires home region DNS and Client-Side Considerations DNS bouncing during a single push is the most common geo-replication push problem in customer threads, and it warrants a section of its own. The failure mode. A docker push is a sequence of HTTP requests: blob uploads for each layer, then a manifest upload that references those layers by digest. If the Linux DNS resolver on the client doesn't cache myregistry.azurecr.io consistently for the duration of the push, individual sub-requests can resolve to different replicas. Because replication is eventually consistent, the manifest can land on a replica that doesn't yet have the layers it references, and the manifest validation fails. The two mitigations: Regional endpoints pin the push to a single replica end-to-end. Every sub-request — login, blob uploads, manifest upload — goes to the same replica. This is the cleanest fix and the one we recommend for any pipeline where push/pull consistency matters. A short-lived client-side DNS cache like dnsmasq scoped to the duration of a single push. For Linux VMs in Azure, follow the DNS name resolution options guidance. The pin should last the push and no longer. For other clients performing pushes, you can customize your stack's DNS resolver to have a similar short-lived DNS cache to pin the global endpoint's resolved DNS for only the duration of an image push operation. A note on long-lived DNS caching for the global endpoint. Don't run a long-lived DNS cache for myregistry.azurecr.io . ACR purges its own DNS records on the server side when a replica is taken out of global routing (Step 3) and during health-aware failover; a long-lived client-side cache will keep clients pointed at the old region after our purge, which makes both the manual disable mechanism and health-aware failover look broken from the client's perspective. Retry behavior: In-flight pushes during a failover may fail. Design publish steps to be idempotent so retries are safe. Pipelines that push in one region and immediately pull from a different region should retry with backoff or check replication status — eventual consistency means the pull may race ahead of replication. ACR is working on bounded staleness consistency that addresses this directly by enabling proxying (on ACR infrastructure) an image pull request from one geo-replica (if it does not have the image) to another geo-replica that has the image; see the relevant FAQ item. Note: Specific retry counts, back-off intervals, and push timeout values are application-layer decisions. The platform behavior is documented; the retry policy belongs to your client. Monitoring Guidance We map the three phases to the signals available from each source. Where a signal requires customer-side configuration, we flag it. Phase A: Initial replication (after creating a new replica) az acr replication list and az acr replication show — confirm the new replica reaches provisioningState: Succeeded and status: online , and view per-replica status. Azure Monitor platform metrics — push count, pull count, and other registry metrics are collected automatically and visible in the Azure portal under Metrics. No customer configuration is needed to view platform metrics. To export metrics or enable resource logs (detailed operation logs), configure Diagnostic Settings on the registry. Phase B: Failover (planned via replica disable, or automatic via health-aware failover) Per-replica regionEndpointEnabled state via az acr replication list — confirms whether a manual disable took effect, i.e. which replicas are currently eligible for global endpoint routing. Note: this flag reflects the manual configuration for configuring a geo-replica's global endpoint routing eligibility; it does not indicate whether health-aware failover has actively rerouted traffic away from a replica. Resource Health for the registry (in the Azure portal under Help > Resource health) — surfaces platform-side degradation signals during incidents. ACR does not yet expose a definitive "this region is currently serving your traffic" signal; Resource Health and client-side latency changes are the best available indicators. Pull latency from clients — increased latency from a more distant replica is the client-observable signal that traffic has rerouted. Azure Monitor platform metrics — visible per-region in the Azure portal Metrics blade. To export metrics or query them programmatically, enable Diagnostic Settings. Phase C: Failback (replica returns to global routing) az acr replication list — confirms regionEndpointEnabled: True (manual) or online status across all replicas (automatic). Pull latency normalizing as clients reach the recovered replica again. Resource Health clearing for the registry (visible in the Azure portal). Note: The health-aware failover blog calls out ongoing work to surface richer signals — including notifications for when routing changes and which region is currently serving your traffic. The signals listed above are what's available today. Pricing Considerations Storage billing vs. storage quota: Storage is billed per geo-replica — a 1 GiB image replicated to 5 geo-replicas is charged as 5 GiB of storage (1 GiB × 5 geo-replicas). However, storage quota (the tier's maximum storage limit) counts the image only once — the same 1 GiB image counts as 1 GiB toward your tier's maximum, not 5 GiB. Data transfer: Geo-replication can reduce costs by enabling in-region image pushes and pulls, which avoids cross-region data transfer charges during these push or pull operations. However, cross-region data transfer charges still apply when ACR replicates pushed content to other geo-replicas as part of eventual consistency. Disabled replicas still cost: When you take a replica out of global routing with --global-endpoint-routing false , storage and per-replica costs continue accruing because data continues syncing bidirectionally. For more information, see ACR pricing. Cleanup Run these commands to undo the walkthrough setup. Order matters: disable regional endpoints before deleting replicas, since regional endpoint URLs depend on which replicas exist. # Disable regional endpoints if you enabled them in Step 2a az acr update -n myregistry -g myrg --regional-endpoints disabled # Re-enable any replicas you disabled in Step 3 (no-op if already enabled) az acr replication update --registry myregistry --name westus \ --global-endpoint-routing true # Delete the West US replica created in Step 1 az acr replication delete --registry myregistry --name westus # Confirm only the home region replica remains az acr replication list --registry myregistry --output table Note: Replica deletion is a control-plane operation that requires the home region to be available. During a home region outage, replica configuration cannot be modified. Summary Table Question Answer When should I use regional endpoints vs the global endpoint? Use regional endpoints (Step 2a) for workloads that need affinity, predictable routing, push/pull consistency, troubleshooting, or client-side failover. Use the global endpoint (Step 2b) for everything else and let health-aware failover handle routing. What should I enable for secure, resilient layer downloads? Enable dedicated data endpoints. They scope firewall rules tightly to your registry and replace wildcard storage DNS with predictable per-region FQDNs. How do I avoid DNS-bouncing manifest validation failures on push? Pin pushes to a single replica via a regional endpoint. A short-lived client-side dnsmasq for the push duration is also fine if you're not using regional endpoints. Should I run a long-lived DNS cache for the global endpoint? No. ACR purges DNS server-side on disable and during failover; client-side caching works against that. Do I need to re-auth when switching endpoints? Yes. Each global or regional endpoint is its own authenticated surface. az acr login , SDK auth, or the Kubernetes ACR credential provider handles the re-auth. What happens during a home region outage? Data plane keeps working through any replica via the global endpoint or regional endpoints. Control plane operations (replica configuration, network rules) are unavailable until the home region recovers. The home region is fixed at registry creation. What's ACR doing about eventual-consistency pain? Bounded staleness consistency for cross-replica pushed images is in development and will be covered in an upcoming blog post. Reach out via GitHub if you want to share your scenario. For the full automation matrix — what's automatic, what requires customer action, and what to expect for each scenario — see the behavior summary above. If you have further questions about ACR geo-replication routing, pinning, capacity planning, eventual consistency, or failover behavior, reach out to us on the Azure Container Registry GitHub repository or file feedback through the Azure portal.
