Conventions used by Containers on Azure App Service
If you have been planning to use containers on Azure App Service, there are some conventions used that helps you get up and running. I have found that they are not all consolidated in one place and there isn’t any dedicate documentation for those conventions. I have seen they are sprinkled throughout the various docs, and this is an attempt to consolidate that information and learn all of the conventions myself.
Expected Exposed Port
Azure App Service for Linux expects that the container runs and exposes its service on port 80 by default. If your application isn’t running on port 80, then you need to the WEBSITES_PORT app setting in your App Service to the port that you are exposing. You can do this will the Azure CLI or with the Azure Portal.
Also, be aware that only one port is currently allowed to be externally exposed on a custom container.
Enabling SSH for the container
You have to configure SSH in your App Service by following these instructions. Keep in mind that you have to make sure you EXPOSE port 2222, this is only available from the Kudu portal.
Here is a collection of different pieces of info that is good to know about running containers. Here are the docs for most info in this section.
Setting Environment Variables in Container
This one isn’t a surprise, environment variables are set for your containers by using app settings.
Nested Structures like JSON
Typically you use nested JSON keys using the colon like this:
However, if you are using Linux or containers, you need to replace that with a double underscore like so.
Accessing App Settings as Environment Variables
Two environment variables are created for each app setting when using PHP, Python, Java, and Node. One will be the name of the setting, and the other will be prefixed with APPPSETTING_SETTING.
Some more peculiar conventions for connection strings. All connection strings have their keys prefixed with the type of the connection string. This is similar to how in .NET you have the type set. Here is the list.
- SQLCONNSTR_ - Sql Server
- SQLAZURECONNSTR_ - Azure SQL
- MYSQLCONNSTR_ - MySQL
- CUSTOMCONNSTR_ - Custom
This one just strikes me as odd, and it seems relatively hidden.
Due to a documented limitation, you cannot run both Windows and Linux apps in the same resource group. I don’t know if I fully understand this one, but it is good to know. If you are having issues be aware of this one.
This is just a quick list of items that I found interesting while learning more about Azure App Service for Linux and using containers with it. I would encourage everyone going this route to follow the links listed above and check out the FAQ. All the information is available, just requires a little digging. Hopefully, this helps others discover this information.
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