Yannick Clybouw

Blog about Full Stack Web Applications

Google App Engine Pro Tip: Use Git Commit Hash as Version

Google App Engine (GAE) is a serverless approach to quickly ship your code. Typically, when you want to deploy, you only need to run one command:

gcloud app deploy

In the Google Cloud Console, you will see a new version of your app appearing, the traffic will be migrated to that new version, and the old version will be shut down.

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List of deployed versions, of which the most recent one is running

By default, versions have a timestamp as name, e.g. 20201204t131734. However, when you want to know what code actually has been deployed, you can only guess it based on that timestamp.

A better approach would be to use your Git commit hash as version. The time of deploy is known anyway (see 5th column in the image). In bash, you can do:

commit_hash=`git rev-parse --short HEAD`

gcloud app deploy --version=$commit_hash

In this example, commit_hash is the short version of the hash of the commit you have currently checked-out.

Of course, this would not make sense if you still have uncommitted changes. To block this, you could use a deploy script, named e.g. deploy.sh, with following content:

#!/usr/bin/env bash

set -e


if [[ -n "$(git status --porcelain)" ]]

then

echo "You have uncommitted changes. Aborting..."

exit 1

fi

commit_hash=`git rev-parse --short HEAD`

gcloud app deploy --version=$commit_hash

Now you know exactly what code has been deployed based on the version name.

There is one remaining caveat: you can still have ignored files. To avoid this, make sure your .gcloudignore file contains at least the patterns of your .gitignore file.