This blog is a follow up to a previous blog I wrote about backing up Azure Analysis Services cubes in Azure, that blog can be found here. This blog shows how to implement a retention policy using PowerShell in Azure Runbooks to remove the backups after a set number of days. To create a new Runbook in the Azure portal, go to the relevant Automation account in the relevant resource group and then select Runbooks from the left hand pane. Note you will need to add the Az.Storage module to the automation account to be able to use some of the commands listed in this blog.
The parameters required here are shown below, where ResourceGroupName is the name of the resource group that has the relevant storage account, StorageAccountName is the name of the storage account resource and ContainerName is the name of the container holding the backup files to be removed. BlobName is part of the name of the files and will be used later to obtain only the relevant files from the storage container. RetentionDays specifies the number of days to keep a backup before it is removed.
The command Set-AzCurrentStorageAccount sets the storage account to be used for the subsequent commands, which gets the container using the ContainerName parameter and then lists the relevant files in the blob container using the BlobName parameter.
Once the list of backup files has been obtained, each file can be checked in turn and removed if it meets the relevant criteria. For each file obtained, the LastModified property is used to identify when the file was created. If the resulting date time is older than the number of retention days from today, the Remove-AzStorageBlob command is used to remove that file from the storage container. This check is repeated for all files, removing the relevant files, and leaving only those that are not older than the RetentionDays parameter.
This is all you need to start cleaning up the backup files in Azure, and although I have used Azure Analysis Services backups for my example here, this code can be used for any blob files in Azure.