chore: automate clean-acr with github action workflow

.github/workflows/clean-acr.yml

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+# Notes: To access key vault and grab the connection string, we first need a service principal.
+# We need to add that service principal as a Reader in the RBAC for the key vault in question,
+# as well as adding it with Get and List permissions in the key vault's access policies.
+# Then we need to store that service principal's info as a GitHub secret.
+# We then use that secret here as the credentials for logging into Azure.
+# Instructions are here: https://learn.microsoft.com/en-us/azure/developer/github/github-key-vault
+# In our case, the service principal is called synapseml-clean-acr.
+# The github secret is a repository secret called clean_acr.
+# It is backed up in the mmlspark-keys vault by secret clean-acr-github-actions-info.
+# The secret has an expiration date (currently 11/20/2024), so it will need to be renewed at some point.
+
+name: Clean ACR
+
+on:
+  schedule:
+    - cron: "0 1 * * 0" # every sunday at 1am
+
+jobs:
+  clean-acr:
+     name: Clean ACR
+     runs-on: ubuntu-latest
+     steps:
+       - name: Azure Login
+         uses: azure/login@v1
+         with:
+           creds: ${{ secrets.clean_acr }}
+       # TODO: The docs say that Azure/get-keyvault-secrets@v1 is deprecated but are vague on what to use instead.
+       # Keep an eye on how this continues to work.
+       - name: Get connection string
+         uses: Azure/get-keyvault-secrets@v1
+         with:
+           keyvault: "mmlspark-keys"
+           secrets: "clean-acr-connection-string"
+         id: getSecret
+       - name: checkout repo content
+         uses: actions/checkout@v2 # checkout the repo
+       - name: setup python
+         uses: actions/setup-python@v4
+         with:
+           python-version: '3.x'
+       - run: pip install azure-storage-blob azure-identity
+       - name: execute clean acr
+         run: python .github/workflows/scripts/clean-acr.py "${{ steps.getSecret.outputs.clean-acr-connection-string }}"
+         shell: sh

.github/workflows/scripts/clean-acr.py

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+import os
+import json
+from azure.storage.blob import BlobClient
+from azure.identity import DefaultAzureCredential
+import sys
+import subprocess
+
+credential = DefaultAzureCredential()
+"""
+run this if sas expires and place result in keyvault under secret name 
+
+ IMPORT_SAS=?$(az storage container generate-sas \
+   --name acrbackup \
+   --account-name mmlspark \
+   --expiry 2023-01-01 \
+   --permissions rawdl \
+   --https-only \
+   --output tsv)
+   echo $IMPORT_SAS
+"""
+
+acr = "mmlsparkmcr"
+container = "acrbackup"
+rg = "marhamil-mmlspark"
+pipeline = "mmlsparkacrexport3"
+
+conn_string = sys.argv[1]
+
+os.system('az extension add --name acrtransfer')
+
+repos = json.loads(os.popen(f"az acr repository list -n {acr}").read())
+for repo in repos:
+    tags = json.loads(os.popen(
+            f"az acr repository show-tags -n {acr} --repository {repo} --orderby time_desc").read())
+
+    for tag in tags:
+        target_blob = repo + "/" + tag + ".tar"
+        image = repo + ":" + tag
+
+        backup_exists = BlobClient.from_connection_string(
+            conn_string, container_name=container, blob_name=target_blob).exists()
+        if not backup_exists:
+            result = os.system(f"az acr pipeline-run create --resource-group {rg} --registry {acr} --pipeline {pipeline} --name {str(abs(hash(target_blob)))} --pipeline-type export --storage-blob {target_blob} -a {image}")
+            assert result == 0
+            print(f"Transferred {target_blob}")
+        else:
+            print(f"Skipped existing {image}")
+
+        backup_exists = BlobClient.from_connection_string(
+            conn_string, container_name=container, blob_name=target_blob).exists()
+        if backup_exists:
+            print(f"Deleting {image}")
+            result = os.system(f"az acr repository delete --name {acr} --image {image} --yes")
+            assert result == 0