Prunes the set of images in an Azure Container Registry.

Delete-AzureContainerImages.ps1

<#
.SYNOPSIS
    Trims down the set of images in an Azure Container Registry.
.DESCRIPTION
    There isn't really a retention policy setting on ACR such that the last X
    tags will be retained for a given repository. This script helps bridge that gap by
    going through all the repositories in an ACR, selecting the latest X tags to ignore,
    then removing tags that were created after that time.
.PARAMETER Registry
    The name of the container registry with the images to prune.
.PARAMETER TagsToKeep
    The number of recent tags to keep.
.PARAMETER RepositoryMatch
    An optional filter regex that allows you to only prune repositories that match the expression.
.EXAMPLE
    ./Delete-AzureContainerImages.ps1 `
      -Registry "sourceacr" `
      -TagsToKeep 5

    This will prune every repository in the `sourceacr` registry. Each repository will
    only keep the most recent five tags.
.EXAMPLE
    ./Delete-AzureContainerImages.ps1 `
      -Registry "sourceacr" `
      -TagsToKeep 5 `
      -RepositoryMatch 'services/accounts/.+'

    This will prune every repository in the `sourceacr` registry that has a name
    matching the regular expression 'services/accounts/.+' - so `services/accounts/test`
    and `services/accounts/spec` will be pruned, but `services/balances/test` will not.
    Only the most recent five tags will be kept.
#>
[CmdletBinding(SupportsShouldProcess = $True, ConfirmImpact = 'High')]
Param(
    [Parameter(Mandatory = $True)]
    [ValidateNotNullOrEmpty()]
    [ValidateLength(5, 50)]
    [ValidatePattern('[a-z0-9]+')]
    [string]
    $Registry,

    [Parameter(Mandatory = $True)]
    [ValidateRange(1, [System.Int32]::MaxValue)]
    [int]
    $TagsToKeep,

    [Parameter(Mandatory = $False)]
    [string]
    $RepositoryMatch
)

Begin {
    Write-Verbose "Checking for az CLI."
    If ($null -eq (Get-Command "az")) {
        Throw "The az CLI was not found. Install here: https://docs.microsoft.com/en-us/cli/azure/install-azure-cli"
        Exit 1
    }
}
Process {
    Write-Progress -Activity "Pruning Azure Container Registry Images" -Status "Getting images from $Registry" -CurrentOperation "Retrieving repository list" -PercentComplete 1
    $RepoListJson = az acr repository list -n $Registry
    If ($LASTEXITCODE -ne 0) {
        Throw "Unable to read repository list from $Registry."
        Exit 1
    }

    $RepoList = $RepoListJson | ConvertFrom-Json -NoEnumerate
    Write-Verbose "Found $($SourceRepoList.Length) repositories in $Registry."
    $ImagesToPrune = @()
    for ($i = 1; $i -le $RepoList.Length; $i++) {
        $RepositoryName = $RepoList[$i - 1]
        $PercentComplete = 25 * ($i / $RepoList.Length)
        Write-Progress -Activity "Pruning Azure Container Registry Images" -Status "Getting image tags from $Registry" -CurrentOperation "Retrieving tags for $RepositoryName" -PercentComplete $PercentComplete
        If ((-not [System.String]::IsNullOrWhiteSpace($RepositoryMatch)) -and (-not ($RepositoryName -match $RepositoryMatch))) {
            Write-Verbose "$RepositoryName does not match against $RepositoryMatch; skipping."
            Continue
        }

        $TagListJson = az acr repository show-tags -n $Registry --repository $RepositoryName --orderby time_desc
        If ($LASTEXITCODE -ne 0) {
            Throw "Unable to read repository tags for $RepositoryName from $Registry."
            Exit 1
        }

        $TagList = $TagListJson | ConvertFrom-Json -NoEnumerate
        Write-Verbose "Found $($TagList.Length) tags for $RepositoryName."
        for ($j = 0; $j -lt $TagList.Length; $j++) {
            If ($j -lt $TagsToKeep) {
                Continue
            }

            $Tag = $TagList[$j]
            $ImagesToPrune += "$RepositoryName`:$Tag"
        }
    }

    for ($i = 1; $i -le $ImagesToPrune.Length; $i++) {
        $ImageName = $ImagesToPrune[$i - 1]
        $PercentComplete = 25 + 75 * ($i / $ImagesToPrune.Length)
        Write-Progress -Activity "Pruning Azure Container Registry Images" -Status "Pruning images" -CurrentOperation "Removing $ImageName" -PercentComplete $PercentComplete
        If ($PSCmdlet.ShouldProcess($ImageName, "Prune image")) {
            az acr repository delete -n $Registry --image $ImageName --only-show-errors -y | Out-Null
            If ($LASTEXITCODE -ne 0) {
                Throw "Failed to prune $ImageName."
                Exit 1
            }
        }
    }

    Write-Progress -Activity "Copying Azure Container Registry Images" -Completed
}