Azure App Service fails to swap deployment slots due to http ping failures

[jchli]

Describe the bug

We have a windows App Service, running .NET 6 in West US. When we deploy our application, it sometimes fails with an error on the "swap slot" operation:

Failed swapping site. Error: Cannot swap site slots for site 'my-site' because the 'blue' slot did not respond to http ping.

It is always the same error, and our blue slot always responds successfully to our pings when we hit it manually during these operations.

Further, this doesn't happen consistently, but started to crop up more often (~40-50% of our deploys across two totally separate directories) since 2024-06-28. We have an open support ticket with azure support, but haven't gotten any information, yet and I wanted to open this up to the community to see who else is getting this problem, especially because the previous two GH issues were closed.

This is highly disruptive for our deployments, because when the swap operation hangs and eventually fails, it will hang for 20+ minutes. However, we have seen that restarting the blue slot while the swap is hanging is one way to get things running again, but we don't think that this is an acceptable long term solution.

Related command

Our deployment commands are approximately:

1. az webapp deployment source config-zip --resource-group rg --name appname --src artifact.zip --slot blue
2. az webapp deployment slot swap -g rg -n appname --slot blue --target-slot production

Errors

Failed swapping site. Error: Cannot swap site slots for site 'my-site' because the 'blue' slot did not respond to http ping.

Issue script & Debug output

These commands are not failing. It is the swap slot operation in Azure that is failing

Expected behavior

Swap should succeed

Environment Summary

azcliversion: 2.30.0

Additional context

• This was reported twice before in GH issues, but closed with no resolution:

1. Function App Slot swap is failing with 'http ping' failure azure-functions-host#8969
2. ZIP deployment failed due to - cannot swap site slots for site because the slot did not respond to http ping Azure-Functions#2264

• We also have an open support ticket with Azure. Ticket ID: 2406280040008216
• We are NOT using App service cache. Our artifact size is 38 MB

[yonzhan]

Thank you for opening this issue, we will look into it.

[microsoft-github-policy-service]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @AzureAppServiceCLI, @antcp.

[microsoft-github-policy-service]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @AzureAppServiceCLI, @antcp.