Guidance on rolling update without downtime

[pragnagopa]

copying from Azure/app-service-announcements-discussions#175 (comment)

cc: @saibaskaran57

Hey everyone,

Could someone share how could we perform the Platform upgrade from Azure Functions v2 -> v3 without any downtimes?

There are two issues I'm currently facing in terms of the platform upgrade:

1. ARM template changes on FUNCTIONS_EXTENSION_VERSION from ~2.0 to ~3 causes downtime with HTTP 503 Service Unavailable
   I did a simple ping check(every 100ms) on my Azure functions when ARM template is being deployed. I could reproduce this using both Powershell & Azure resource group deployment azure pipeline task as show below:
   

2. I've changed my strategy to upgrade using Functions deployment staging slots first before making a swap. However, the FUNCTIONS_EXTENSION_VERSION app settings did not bring forward to production slot during this swap.
   Just to test this out, in my staging slot I updated FUNCTIONS_EXTENSION_VERSION from ~2.0 to ~3 and created a new app settings called NewVar. From the screenshot below, only NewVar is brought forward to production slot.
   

How can we ensure the function app is upgraded with seamless approach without causing service downtime?

Thanks.

[saibaskaran57]

Thank you @pragnagopa . Appreciate for your help.

[pragnagopa]

@anthonychu - Are you aware of any best practices doc for zero downtime deployment while using slots?

[saibaskaran57]

Hello @pragnagopa @anthonychu ,

Do we have any best practices document for the above? I'm leveraging Azure App Service for my function deployment. I suppose deployment slots always help us to solve this type of issues but for this scenario, it does not as the FUNCTIONS_EXTENSION_VERSION is not swapped.

Thanks.