Azure Deployment Slot Troubleshooting

Intro

Over the past year, we have moved many clients over to using Azure Deployment Slots.

When setting up deployment slots there are a few common issues that you can run into. I'll cover each of them in this blog and provide advice for how they can be resolved.

Site Restart On Swap

This is a common issue with deployment slots whenever you initiate a swap, the production site will be restarted causing an outage.

To counter-act this issue, add the following setting to your application settings on your App Service:

This needs to be added to the production slot and the backup slot, I would reccomend adding it to your backup slot first, and after you intiate your first swap, add it to the new backup slot. There is potential downtime when changing settings in your App Service.

Cannot Swap Slots Due To 'Another Operation Is In Progress'

This issue occurs when you attempt to swap with a specfic setting enabled on the deployment slot.

This is a more recent issue we have seen recently, luckily this is an easy fix, if you are copying App settings over, make sure to not include the WEBSITE_LOCAL_CACHE_OPTION in the backup slot. To make sure this setting persists during a swap, enable it as a deployment slot setting in your main site slot.

Closing

Hopefully our experiences with deployment slots helps you avoid the issues we have had in the future.