Migrating Teams Calling Bot (EchoBot) from VMSS to Windows Containers / ACI?

AKS is the only container option I would treat as supported here. The current Teams documentation lists AKS, but the application-hosted media requirements still apply: Windows Server, a ready instance, direct internet reachability with an instance-level public IP and public-facing port, and calls pinned to the instance that accepted them. ACI is not in the supported-host list, and its networking/lifecycle model does not map cleanly to that per-instance requirement.

I would not start an ACI container only after the call arrives. Provisioning and image-pull time make call setup unreliable, and stopping the worker ends any active call. A practical cost-optimized design is a Windows AKS node pool or VMSS with one warm worker, scale out on call/concurrency metrics, and drain calls before scale-in. It will not reach zero idle cost, but it preserves the supported media path.

If you only need prompts, DTMF, or short recordings rather than continuous raw audio, check whether service-hosted media can replace the local Media SDK—that is the real near-zero-infrastructure option.

https://learn.microsoft.com/en-us/microsoftteams/platform/bots/calls-and-meetings/requirements-considerations-application-hosted-media-bots