Lessons Learned #551: Azure SQL Connection Timeouts: Three Things to Check
An application starts reporting intermittent timeouts when connecting to Azure SQL Database. Some requests succeed, others fail, and a test from a developer’s laptop works perfectly. The database appears online, no recent deployment seems related, and the natural reaction is to ask: Is Azure SQL unavailable? Is the firewall blocking the connection? Should we increase the connection timeout? Should we change the driver or scale the database? Those are reasonable questions, but they may lead the investigation in the wrong direction. The most important lesson is simple: A timeout tells us how long the application waited. It does not tell us what the application was waiting for. Not every “SQL timeout” happens inside Azure SQL From the application’s point of view, opening a database connection may involve several operations: Resolving the server name. Reaching the SQL endpoint. Obtaining a Microsoft Entra access token. Waiting for an available pooled connection. Completing the SQL login. Executing the first command. When all these operations are reported through the same application method or log entry, it can look as though Azure SQL took thirty seconds to accept the connection. In reality, only part of that time may have been spent connecting to the database. In one anonymized support scenario, the application experienced problems mainly on its first connection. Network tests were successful and no corresponding SQL connection failure was identified. The investigation eventually showed that access-token acquisition was consuming a significant part of the available time. Increasing the SQL timeout or changing the firewall would not have addressed the real delay. Check 1: Capture the complete error and the exact time A screenshot containing only “Connection Timeout Expired” is rarely enough. Capture: The complete exception and inner exception. The operation being performed. The driver and version. The authentication method. The exact timestamp in UTC. Whether the issue affects every connection or only some of them. The wording around the timeout matters. For example, a timeout while obtaining a connection from the pool points toward the application’s pooling and concurrency behavior. A pre-login or TLS error belongs to a different investigation. A command timeout after the connection was established is usually a query-performance problem rather than a connection problem. Check 2: Measure the application timeline The application should record important operations separately. A simple timeline can completely change the investigation: 10:14:20.100 Token acquisition started 10:14:28.400 Token acquired 10:14:28.405 SQL connection started 10:14:29.050 SQL connection established The complete operation took almost nine seconds, but Azure SQL connection establishment took less than one second. Useful measurements include: Token-acquisition duration. Time waiting for a pooled connection. SQL connection-open duration. SQL command duration. Number of retry attempts. Applications using Microsoft Entra authentication must obtain an access token before authenticating to Azure SQL. Measuring that operation separately helps distinguish an identity delay from a database connectivity problem. This is particularly useful when the issue appears: On the first connection after startup. After a token expires. Only with Managed Identity or Workload Identity. Intermittently, while SQL authentication connections remain unaffected. Check 3: Test from the application environment A successful connection from a laptop does not validate the path used by an application running in: Azure App Service. Azure Functions. Azure Kubernetes Service. A virtual machine. An on-premises application server. A container or integration runtime. The laptop and the application may use different DNS servers, routes, firewalls, proxies and identities. Connectivity and DNS tests should therefore be performed from the environment that is actually failing. This becomes especially important when Private Endpoint is used. The application should continue connecting with: <server>.database.windows.net It should not use the Private Endpoint IP address or the privatelink.database.windows.net hostname directly. Direct login attempts using the private IP or the private-link FQDN fail; the normal logical-server FQDN must remain in the connection string. From the affected environment, confirm that: The expected DNS server answers the request. The server FQDN resolves to the expected private IP. The Private Endpoint connection is approved. The Private DNS zone is linked correctly. The resolved address is reachable through the intended route. A test from an unrelated machine is still useful for comparison, but it does not prove that the application path is healthy. Observed symptom Likely investigation area Timeout while obtaining a connection from the pool Application connection pooling Server name cannot be resolved DNS TCP connection to the endpoint cannot be established Network path, firewall or routing Error during the pre-login handshake TLS, driver, network interruption or pre-login processing Authentication or access-token error Microsoft Entra authentication, identity or token acquisition Timeout during the post-login phase Login completion, session initialization or server-side processing Execution or command timeout after connecting Query execution and database performance Avoid changing several things at once During a production incident, it is tempting to: Increase the timeout. Add firewall rules. Change the connection policy. Upgrade the driver. Restart the application. Clear connection pools. Applying several changes together makes it difficult to determine which one helped, and some may only hide the symptom. A better approach is to define one hypothesis: We believe DNS in the application environment is resolving the public endpoint instead of the Private Endpoint. Then define: The evidence supporting the hypothesis. One controlled change. The expected result. How the result will be measured. How the change will be reverted. Azure SQL supports Proxy and Redirect connection policies, which determine how traffic flows after reaching the Azure SQL gateway. The policy is configured for the logical server, so it should be verified before making firewall assumptions or changes. What should we collect before opening a support request? A small but precise evidence package can avoid several rounds of questions: Complete error and inner exception. Exact UTC timestamps. Application platform and location. Public or Private Endpoint. Server FQDN used by the application. Driver and version. Authentication method. Token, pool, connection and command durations. DNS result from the affected environment. Whether the issue is constant, intermittent or limited to the first connection. Recent application, network, identity or configuration changes.
SQL MI Private Endpoint in One Picture
PRIVATE ENDPOINT – SQL MANAGED INSTANCE Where PE can be located? Key points Connections only in one direction, from PE to SQL MI and traffic in port 1433 When using PE, there’s no need to set up VNET peering or public endpoint Connection string needs SQL MI hostname / IP address is not supported Customer DNS or Azure DNS private zone is needed PE establishes secure and isolated connectivity PE always use proxy connection type PE can be created in different Azure tenant When connecting from same VNET than SQL MI, TLS certificate configuration needed Article link - https://learn.microsoft.com/en-us/azure/azure-sql/managed-instance/private-endpoint-overview?view=azuresql&tabs=separate-vnetsHow to automate the deployment of an Elastic Job Agent with a Private Endpoint via Bicep
Environment Overview Recently, I worked on a case where our customer encountered an issue during the deployment of an Elastic Job Agent (EJA) and a Private Endpoint (PEP) using a Bicep deployment script. The process resulted in an endless deployment loop. In this article, I will guide you step by step through creating an EJA with a PEP and demonstrate how to automatically approve the connection using a Bicep deployment script. Technical Issue The main challenge is that the EJA PEP is fully managed by Microsoft, which means you cannot specify a name during the script authorization process—the system assigns one randomly. To address this, we will use deploymentScripts in combination with PowerShell to monitor and authorize the process automatically. For more details, please refer to the following resources: References Use deployment scripts in Bicep https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/deployment-script-bicep?tabs=azure-cli Elastic jobs in Azure SQL Database https://learn.microsoft.com/en-us/azure/azure-sql/database/elastic-jobs-overview?view=azuresql Elastic job private endpoints https://learn.microsoft.com/en-us/azure/azure-sql/database/elastic-jobs-overview?view=azuresql#elastic-job-private-endpoints The Idea Since it's not possible to specify the EJA PEP name as a variable for direct approval—unlike standard PEPs—the approach was to intercept the auto-generated PEP by its ID or name and then authorize it automatically. (Remember to always follow the Principle of Least Privilege (PoLP)); in my example, I used Contributor permissions for simplicity. ****************************************************************************************************************************************************************************************************** /*Disclaimer: ****************************************************************************************************************************************************************************************************** This script is not supported under any Microsoft standard support program or service. This script is provided AS IS without warranty of any kind. Microsoft further disclaims all implied warranties including, without limitation, any implied warranties of merchantability or of fitness for a particular purpose. The entire risk arising out of the use or performance of the script and documentation remains with you. In no event shall Microsoft, its authors, or anyone else involved in the creation, production, or delivery of the script be liable for any damages whatsoever (including, without limitation, damages for loss of business profits, business interruption, loss of business information, or other pecuniary loss) arising out of the use of or inability to use the current script or documentation, even if Microsoft has been advised of the possibility of such damages. I’m not a programmer or a Bicep expert. I simply put together what I was able to reason through in order to meet our client’s request. Any suggestions or modifications are welcome. ****************************************************************************************************************************************************************************************************** This article was written in August 2025; code and modules may change over time. ****************************************************************************************************************************************************************************************************** */ param prefix string = 'bicep' param environment string = 'test' param sqlServerName string = 'bicep-test-sqleja-sqlsrv' param location string = 'westeurope' param forceUpdateTag string = utcNow() //let's check that the previously manually created server is present resource sqlServer 'Microsoft.Sql/servers@2021-11-01' existing = { name: sqlServerName } //create the database resource sqlDb 'Microsoft.Sql/servers/databases@2021-11-01' = { parent: sqlServer name: '${prefix}-${environment}-sqleja-sqldb' location: location properties: { requestedBackupStorageRedundancy: 'Local' maxSizeBytes: 5368709120 } sku: { name: 'S3' } } //create the Job Agent resource sqlJob 'Microsoft.Sql/servers/jobAgents@2024-05-01-preview' = { parent: sqlServer location: location name: '${prefix}-${environment}-sqleja-sqljobagent' properties: { databaseId: sqlDb.id } sku: { name: 'JA100' } } //defines a Target Group within a Job Agent resource targetGroup 'Microsoft.Sql/servers/jobAgents/targetGroups@2024-05-01-preview' = { parent: sqlJob name: '${prefix}-${environment}-sqleja-targetgroup' properties: { members: [ { membershipType: 'Include' serverName: sqlServer.name type: 'SqlServer' } ] } } //generate an UMI to auth and deploy the PS script resource scriptIdentity 'Microsoft.ManagedIdentity/userAssignedIdentities@2023-01-31' = { name: '${prefix}-${environment}-deployscript-umi' location: location } //assign the role to the script UMI //https://learn.microsoft.com/en-us/azure/role-based-access-control/built-in-roles resource scriptRoleAssignment 'Microsoft.Authorization/roleAssignments@2022-04-01' = { name: guid(scriptIdentity.id, 'script-role-assignment') properties: { roleDefinitionId: subscriptionResourceId('Microsoft.Authorization/roleDefinitions', 'b24988ac-6180-42a0-ab88-20f7382dd24c') // Contributor principalId: scriptIdentity.properties.principalId } dependsOn: [ delayScript ] } //let's generate a delay to allow Azure AD permissions propagation resource delayScript 'Microsoft.Resources/deploymentScripts@2023-08-01' = { name: 'sleep-60s-bash' location: location kind: 'AzureCLI' identity: { type: 'UserAssigned' userAssignedIdentities: { '${scriptIdentity.id}': {} } } properties: { azCliVersion: '2.76.0' scriptContent: ''' echo "Sleeping for 60 seconds..." sleep 60 echo "Done sleeping." ''' retentionInterval: 'P1D' cleanupPreference: 'Always' timeout: 'PT5M' forceUpdateTag: forceUpdateTag } dependsOn: [ scriptIdentity ] } //create the eja pep resource privateEndpoint 'Microsoft.Sql/servers/jobAgents/privateEndpoints@2024-05-01-preview' = { parent: sqlJob name: '${prefix}-${environment}-sqleja-pep' properties: { targetServerAzureResourceId: sqlServer.id } } //PS script to approve the MS fully managed PEP resource approvePrivateEndpointConnection 'Microsoft.Resources/deploymentScripts@2023-08-01' = { name: 'ps-to-approve-eja-pep-by-script' location: location kind: 'AzurePowerShell' identity: { type: 'UserAssigned' userAssignedIdentities: { '${scriptIdentity.id}': {} } } properties: { azPowerShellVersion: '11.0' scriptContent: ''' Connect-AzAccount -Identity $SqlServerResourceIdForPrivateLink = '/subscriptions/<yourSubID>/resourceGroups/bicep-rg/providers/Microsoft.Sql/servers/bicep-test-sqleja-sqlsrv' $SQLprivateEndpoints = Get-AzPrivateEndpointConnection -PrivateLinkResourceId $SqlServerResourceIdForPrivateLink foreach ($privateEndpoint in $SQLprivateEndpoints) { if ($privateEndpoint.PrivateLinkServiceConnectionState.Status -eq "Pending") { $id = $privateEndpoint.id Write-Output "Approving Private Endpoint Connection: $id" Approve-AzPrivateEndpointConnection -ResourceId "${id}" -Description "Approved by Bicep Deployment Script" } } ''' retentionInterval: 'P1D' cleanupPreference: 'Always' timeout: 'PT30M' forceUpdateTag: forceUpdateTag } dependsOn: [ sqlJob scriptRoleAssignment ] } Deployment Details Below is an overview of the resources created by the automation Conclusion With this article, I’ve wanted to share how to automate the creation of an Elastic Job Agent Private Endpoint without requiring manual approval. Kindly note that the products and options presented in this article are subject to change, this article reflects for Azure SQL Database in September 2025. Please also make sure to review the code carefully. It is provided as-is, with no guarantees, warranties, or support. Any suggestions or improvements are welcome. I hope you find this guide useful and that it inspires you to experiment freely with your deployments. Thank you. Best Regards, VittorioLesson Learned #517:Connection Timeouts to Azure SQL Database Using Private Endpoint with HikariCP
Recently, we have been working on a support case where our customer reported the following error message: ERROR com.zaxxer.hikari.pool.HikariPool - HikariPool-1 - Exception during pool initialization. com.microsoft.sqlserver.jdbc.SQLServerException: The TCP/IP connection to the host myserverX.database.windows.net, port 1433 has failed. Error: 'Connection timed out: no further information. Verify the connection properties. Make sure that an instance of SQL Server is running on the host and accepting TCP/IP connections at the port. Make sure that TCP connections to the port are not blocked by a firewall.' I would like to share the lessons learned during the troubleshooting and resolution process Initially, what caught our attention were the first two messages: Exception during pool initialization and Connection Timeout out. This indicates that Hikari was unable to create the connection pool during the initialization process (one of the first steps in connection pooling) due to a connection timeout. Therefore, we began working on connectivity options and started investigating, asking if our customer is using public endpoint or private endpoint, they confirmed the private endpoint usage. The following factors could be identified as possible causes: Private Endpoint Misconfiguration: The Private Endpoint was not correctly associated with the Azure SQL Database. DNS Resolution Issues: The database hostname was not resolving to the Private Endpoint's private IP address. Network Security Group (NSG) Restrictions: The NSG attached to the subnet hosting the Private Endpoint was blocking inbound traffic on port 1433. Firewall Settings on Azure SQL Database: Firewall rules were not allowing connections from the source network. Redirect Mode Configuration: Additional ports required for redirect mode were blocked or misconfigured. Our troubleshooting steps started running using nslookup myserverX.database.windows.net to ensure that the database hostname resolves to the Private Endpoint's private IP address. If the IP is public instead of private, we verify the DNS configuration or use Azure DNS. Our second step was to validate the Java Application host can reach Azure SQL Database on port 1433 or the redirect port (if our customer use redirect connection policy) using the command telnet myserverX.database.windows.net 1433 or the Linux command nc -vz myserverX.database.windows.net 1433 and we identified the connections fails. Check this Azure SQL Database and Azure Synapse Analytics connectivity architecture and Azure Private Link - Azure SQL Database & Azure Synapse Analytics | Microsoft Learn for more details. Following we verify the Network Security Group attached to the subnet if allows outbound traffic to the port 1433 and we found that the NSG rule doesn't exist for private endpoint. Once the rule was added the Java Application was able to connect.Transition from VNET integration to public access or Private Link using the Azure CLI
This post provides two bash scripts that use the Azure CLI to transition an Azure Database for MySQL flexible server from VNET Integrated to Public Access or a Private Link. You can run these bash scripts either locally or by using the Azure Cloud Shell.
Azure Data Factory Linked Service to connect Batch Account and Node with private endpoint
HI All, I am trying to connect batch account and batch pool from Azure Data Factory where batch pool is configured in private network. Steps followed. 1. created private link service to connect batch account and node by adding the domain names of batch account and node 2. tried to establish connection but it failed to connect to batch pool (pool with virtual network). I am not clear on the steps to be implemented in loan balancer which needs to be configured for private links service. I have added front end ip as Virtual network IP, backend pool as batch pool ip. I couldn't find proper document for this setup. please help if anyone come across this scenario or any document which explains in detail. Thanks, SathishAzure SQL DB Private Link / Private Endpoint - Connectivity Troubleshooting
In the article Azure SQL DB Connectivity Troubleshooting we have explored regular connectivity troubleshooting to Azure SQL DB, on this one we will explore connectivity troubleshooting using Private Link In this article we are going to explore What is the Private Endpoint for Azure DB? Creation of Private Endpoint Azure VM > Private Link OnPrem VM > VPN (P2S) > Private Link (Hosts File) OnPrem VM > VPN (P2S) > Private Link (Custom DNS) Azure Function > VNET integration > Private Endpoint Failover Groups with Private Link 1 - What is the Private Endpoint for Azure DB? Azure Private Link enables you to access Azure PaaS Services (for example, Azure Storage and SQL Database) and Azure hosted customer-owned/partner services over a private endpoint in your virtual network. Traffic between your virtual network and the service travels the Microsoft backbone network. Exposing your service to the public internet is no longer necessary Some important information Private Link service can be accessed from approved private endpoints in the same region. The private endpoint can be reached from the same virtual network, regionally peered VNets, globally peered VNets and on premises using private VPN or ExpressRoute connections. When creating a Private Link Service, a network interface is created for the lifecycle of the resource. This interface is not manageable by the customer. The Private Link Service must be deployed in the same region as the virtual network. A single Private Link Service can be accessed from multiple Private Endpoints belonging to different VNets, subscriptions and/or Active Directory tenants. The connection is established through a connection workflow. In the image, below we can see how the connection using private endpoint works. And as mentioned on the other article Azure SQL DB Connectivity Troubleshooting the Azure SQL DB clients by default will all go to the Shared public IP of the regional gateway. With the private endpoint you can close this public path and users can only connect from private endpoint. If you have multiple Azure VNETs you will need to use VNET peering or VNET VPN between two Azure VNETs, or P2S,S2S or Express Route to connect your onprem to Azure Network 2 - Creation of Private Endpoint To create a Private endpoint just follow up the procedure documented at https://docs.microsoft.com/en-us/azure/private-link/create-private-endpoint-portal You may also want to close all public network access to make sure all connection must flow from Private Endpoint. Just need to go to Azure SQL DB instance and "Firewall and Virtual Networks" and Deny public network access. Find below the procedure I've used to create a Private Endpoint Just need to go to "Private Endpoint Connections" and then add a Private endpoint Select the region that should be the same as the VNET region as mentioned above. Select the resource type "Microsoft.Sql/servers" for Azure SQL DB instance Select the Azure SQL DB instance you want to connect Select the VNET / Subnet. Notice also that during the creation you can already create a private DNS zone, that will work for Azure resources that uses the Azure DNS. We will talk more about that when doing the tests 3 - Azure VM > Private Endpoint From an Azure VM deployed to same VNET, if we test command below on command prompt before you create the Private Endpoint. nslookup fonsecanet-westeu.database.windows.net You will get result like below that shows that this server is using public gateway IP: 40.68.37.158. So NOT using any private IP Server: UnKnown Address: 168.63.129.16 Non-authoritative answer: Name: westeurope1-a.control.database.windows.net Address: 40.68.37.158 Aliases: fonsecanet-westeu.database.windows.net After you create the Private Endpoint using the same command above you are expected to see the results below Server: UnKnown Address: 168.63.129.16 Non-authoritative answer: Name: fonsecanet-westeu.privatelink.database.windows.net Address: 10.0.1.4 Aliases: fonsecanet-westeu.database.windows.net Be sure also to open outbound communication from Azure VM VNET to Private Endpoint on Local Firewall, Corporate Firewall, or Azure NSGs. For this test I've opened to allow all communication inside VNET. *Currently (Status on 2020-04-06) redirect is not supported, so only needed 1433 port You must use the FQDN to connect to Azure SQL DB as documented at https://docs.microsoft.com/en-us/azure/sql-database/sql-database-private-endpoint-overview#check-connectivity-using-sql-server-management-studio-ssms Use the Fully Qualified Domain Name (FQDN) of the server in connection strings for your clients. Any login attempts made directly to the IP address shall fail. This behavior is by design, since private endpoint routes traffic to the SQL Gateway in the region and the FQDN needs to be specified for logins to succeed. You can also check if connection is correct using TSQL below. And we will see the client IP is the private IP assigned to Azure VM. SELECT client_net_address FROM sys.dm_exec_connections where session_id = @@SPID You must use the FQDN to connect to Azure SQL DB. Azure SQL DB gateway use the name to route correctly your connection to the SQL host, when information is not provided it will fail If you try to connect using private endpoint IP you are going to get error like below =================================== Cannot connect to 10.0.1.4. =================================== A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The target principal name is incorrect.) (.Net SqlClient Data Provider) ------------------------------ Server Name: 10.0.1.4 Error Number: -2146893022 Severity: 20 State: 0 You should also NOT use DB.privatelink.database.windows.net =================================== Cannot connect to fonsecanet-westeu.privatelink.database.windows.net. =================================== A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The target principal name is incorrect.) (.Net SqlClient Data Provider) ------------------------------ Server Name: fonsecanet-westeu.privatelink.database.windows.net Error Number: -2146893022 Severity: 20 State: 0 4 - OnPrem VM > VPN (P2S) > Private Link (Hosts File) You can use some template like below to create the VPN Point to Site https://docs.microsoft.com/en-us/azure/sql-database/sql-database-managed-instance-configure-p2s https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-howto-point-to-site-resource-manager-portal After creating the VPN, downloading and installing the VPN client and connecting to it If I check name resolution nslookup fonsecanet-westeu.database.windows.net We can see that it is still using Microsoft internal Corporate DNS where this VM is located Server: XXXXXXXXXXX.corp.microsoft.com Address: 10.221.xx.xx Non-authoritative answer: Name: westeurope1-a.control.database.windows.net Address: 40.68.37.158 Aliases: fonsecanet-westeu.database.windows.net fonsecanet-westeu.privatelink.database.windows.net For this scenario you will need to use your corporate DNS to have the name resolution https://docs.microsoft.com/en-us/azure/private-link/private-endpoint-overview#dns-configuration When connecting to a private link resource using a fully qualified domain name (FQDN) as part of the connection string, it's important to correctly configure your DNS settings to resolve to the allocated private IP address. Existing Azure services might already have a DNS configuration to use when connecting over a public endpoint. This needs to be overridden to connect using your private endpoint. The network interface associated with the private endpoint contains the complete set of information required to configure your DNS, including FQDN and private IP addresses allocated for a given private link resource. You can use the following options to configure your DNS settings for private endpoints: Use the Host file (only recommended for testing). You can use the host file on a virtual machine to override the DNS. Use a private DNS zone. You can use private DNS zones to override the DNS resolution for a given private endpoint. A private DNS zone can be linked to your virtual network to resolve specific domains. Use your custom DNS server. You can use your own DNS server to override the DNS resolution for a given private link resource. If your DNS server is hosted on a virtual network, you can create a DNS forwarding rule to use a private DNS zone to simplify the configuration for all private link resources. Important It's not recommended to override a zone that is actively in use to resolve public endpoints. Connections to resources won't be able to resolve correctly without DNS forwarding to the public DNS. To avoid issues, create a different domain name or follow the suggested name for each service below. Private Link resource type Subresource Zone name SQL DB (Microsoft.Sql/servers) Sql Server (sqlServer) privatelink.database.windows.net Azure will create a canonical name DNS record (CNAME) on the public DNS to redirect the resolution to the suggested domain names. You'll be able to override the resolution with the private IP address of your private endpoints. Your applications don't need to change the connection URL. When attempting to resolve using a public DNS, the DNS server will now resolve to your private endpoints. The process does not impact your applications. For this test will use HOST file solution And we are able to connect fine. And as before you will be able to check you get the VPN ip range using TSQL below SELECT client_net_address FROM sys.dm_exec_connections where session_id = @@SPID 5 - OnPrem VM > VPN (P2S) > Private Link (Custom DNS) If you do not want to use local hosts file as mentioned above you can add Azure DNS (168.63.129.16) as a forwarder on your custom DNS For more information about more complex DNS relationships follow up the official documentation https://docs.microsoft.com/en-us/azure/private-link/private-endpoint-dns On Azure Virtual Network settings I've replaced default Azure DNS with your custom DNS (On my tests 10.0.0.5). You can also add 168.63.129.16 (Azure DNS) as secondary DNS just in case 1st is off If your client lives in Azure, the DNS on VM can be a forwarder to Azure DNS - Go to DNS > Domain > Properties > Forwarders - Add Azure DNS (168.63.129.16) Do not forget to add virtual network link from Private Zone to the VNET where your Azure VM with DNS lives. If you are have onprem DNS you may need a Conditional forwarder Go to DNS > Domain > Conditional Forwarders > New DNS Domain should be database.windows.net. DO NOT USE privatelink.database.windows.net And you can check if name resolution works fine nslookup fonsecanet-westeu.database.windows.net Server: fonsecanetad.internal.cloudapp.net Address: 10.0.0.5 Non-authoritative answer: Name: fonsecanet-westeu.privatelink.database.windows.net Address: 10.0.1.4 Aliases: fonsecanet-westeu.database.windows.net If do not want to use forwarder you can also create a forward lookup zone and added manually the host to match the FQDN 6 - Azure Function > VNET integration > Private Endpoint To make Azure Function to connect to private endpoint you will need to use VNET integration https://docs.microsoft.com/en-us/azure/azure-functions/functions-create-vnet https://docs.microsoft.com/en-us/azure/app-service/web-sites-integrate-with-vnet *Status on (2020-04-27) There was some limitation on webapp + private DBS that are now gone and just need to set some configurations as documented at https://docs.microsoft.com/en-us/azure/app-service/web-sites-integrate-with-vnet#azure-dns-private-zones After your app integrates with your VNet, it uses the same DNS server that your VNet is configured with. By default, your app won't work with Azure DNS Private Zones. To work with Azure DNS Private Zones you need to add the following app settings: WEBSITE_DNS_SERVER with value 168.63.129.16 WEBSITE_VNET_ROUTE_ALL with value 1 These settings will send all of your outbound calls from your app into your VNet in addition to enabling your app to use Azure DNS private zones. And I've also created a sample Azure Function app that accept the connection string as parameter and was able to connect fine You can check the source code at https://github.com/FonsecaSergio/AzureFunctionAppTestConnectivity 7 - Failover Groups with Private Link For this scenario I will just reference link from Product Group article https://techcommunity.microsoft.com/t5/azure-sql-database/using-failover-groups-with-private-link-for-azure-sql-database/ba-p/1272902 Be sure to config private zone network link to both networks https://docs.microsoft.com/en-us/azure/private-link/private-endpoint-dns#virtual-network-workloads-without-custom-dns-server This model can be extended to multiple peered virtual networks that are associated to the same private endpoint. This can be done by adding new virtual network links to the private DNS zone for all peered virtual networks. Result for my tests C:\Users\FonsecaSergio>nslookup SERVER1.database.windows.net Server: UnKnown Address: 168.63.129.16 Non-authoritative answer: Name: SERVER1.privatelink.database.windows.net Address: 12.1.1.6 Aliases: SERVER1.database.windows.net C:\Users\FonsecaSergio>nslookup SERVER2-westus.database.windows.net Server: UnKnown Address: 168.63.129.16 Non-authoritative answer: Name: SERVER2-westus.privatelink.database.windows.net Address: 11.0.1.4 Aliases: SERVER2-westus.database.windows.net C:\Users\FonsecaSergio>nslookup FAILOVERGROUP.database.windows.net Server: UnKnown Address: 168.63.129.16 Non-authoritative answer: Name: SERVER1.privatelink.database.windows.net Address: 12.1.1.6 Aliases: FAILOVERGROUP.database.windows.net SERVER1.database.windows.net For DNS on more complex environments, please follow up other scenarios as mentioned at https://docs.microsoft.com/en-us/azure/private-link/private-endpoint-dns REF and LINKS https://docs.microsoft.com/en-us/azure/private-link/private-link-service-overview https://docs.microsoft.com/en-us/azure/private-link/private-endpoint-overview https://docs.microsoft.com/en-us/azure/sql-database/sql-database-private-endpoint-overview https://docs.microsoft.com/en-us/azure/private-link/ https://docs.microsoft.com/en-us/azure/app-service/web-sites-integrate-with-vnet#enable-vnet-integration https://channel9.msdn.com/Shows/Data-Exposed/Private-Link-for-Azure-SQL-Database-Part-1?term=Private%20Link%20for%20Azure%20SQL%20Database&lang-en=true https://channel9.msdn.com/Shows/Data-Exposed/Private-Link-for-Azure-SQL-Database-Part-2?term=Private%20Link%20for%20Azure%20SQL%20Database&lang-en=true
