On triggered build, write git commit to front end

cloudbuild.yaml

@@ -9,15 +9,27 @@
 # Example invocation:
 # `gcloud builds submit --config=cloudbuild.yaml --substitutions=_ZONE=us-central1-b,_CLUSTER=demo-app-staging .`
 
+steps:
+- id: 'Write git commit to frontend'
+  name: 'ubuntu'
+  entrypoint: 'bash'
+  args:
+  - '-c'
+  - |
+    tools/insert_git_commit_link.sh
+  env:
+  - "COMMIT_SHA=$COMMIT_SHA"
+  - "SHORT_SHA=$SHORT_SHA"
+
 steps:
 - id: 'Deploy application to cluster'
   name: 'gcr.io/k8s-skaffold/skaffold:v0.20.0'
   entrypoint: 'bash'
   args: 
   - '-c'
-  - > 
-    gcloud container clusters get-credentials --zone=$_ZONE $_CLUSTER;
-    skaffold run -f=skaffold.yaml --default-repo=gcr.io/$PROJECT_ID;
+  - |
+    gcloud container clusters get-credentials --zone=$_ZONE $_CLUSTER
+    skaffold run -f=skaffold.yaml --default-repo=gcr.io/$PROJECT_ID
 
 # Add more power, and more time, for heavy Skaffold build
 timeout: '3600s'

src/frontend/templates/footer.html

@@ -4,7 +4,7 @@
             <p>
                 &copy; 2018 Google Inc
                 <span class="text-muted">
-                    <a href="https://github.com/GoogleCloudPlatform/microservices-demo/">(Source Code)</a>
+                    (<a href="https://github.com/GoogleCloudPlatform/microservices-demo/">Source Code</a><!--GIT_COMMIT_LINK-->)
                 </span>
             </p>
             <p>

tools/insert_git_commit_link.sh

@@ -0,0 +1,12 @@
+# when project is built by Cloud Build from a source trigger, the 
+# commit SHA will be available as an env var
+
+if [[ "$COMMIT_SHA" && "$SHORT_SHA" ]]; then
+    target="<!--GIT_COMMIT_LINK-->"
+    replace=" [<a href='https://github.com/GoogleCloudPlatform/microservices-demo/commit/${COMMIT_SHA}'\
+             style='font-size:80%'>${SHORT_SHA}</a>]#"
+
+    sed -i'' -e "s^$target^$replace^g" src/frontend/templates/footer.html
+
+    cat src/frontend/templates/footer.html
+fi