We have an Azure Function v3 instance on a Consumption plan which includes a staging slot to reduce downtime during deployments.
Our deployment process is:
- deploy the code to the staging slot
- start the staging slot
- swap the staging slot with the production one
- stop the staging slot
We are using Azure Pipelines to deploy the code, .NET Core 3.1, to the staging slot; here is the YAML definition for this step:
- task: AzureFunctionApp@1
displayName: 'Deploy to Staging Slot'
inputs:
azureSubscription: '****'
appType: functionApp
appName: '****'
package: '$(System.ArtifactsDirectory)/Build.zip'
deployToSlotOrASE: true
slotName: 'staging'
resourceGroupName: '****'
I have disabled all the steps after this one and run ONLY this step. Once the step completes in Azure Pipelines, the main app, i.e. the production slot, restarts and I start receiving 503 Service Unavailable for about 5 seconds followed by a cold start.
What I don't understand is how deploying the code to the staging slot without swapping can cause a restart on the production slot.
I have made sure that auto-swap is disabled, so that's not the case.
How can it be explained and fixed? We are trying to remove the 503 entirely and have zero-downtime deployments.
Update: I have already tried adding WEBSITE_ADD_SITENAME_BINDINGS_IN_APPHOST_CONFIG to both staging and production slot. Didn't make a difference.