Ross Guarino

Infrastructure, Resiliency and human factors

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Firebase Custom Builder for Google Container Builder
4 minutes read

Google Container Builder — or as my subconscious likes to call it google cloud builder — has support for running arbitrary build steps. Something I needed but couldn’t find was a build step for publishing a site to Firebase’s Hosting product.

I’ve created a custom build step for Firebase that you can use in your builds.

edit: Shortly after I published this a firebase builder was added to the community builders repository!

I highly recommend you use that instead of mine. Everything in this post except the immediate code block is still accurate so I’ve left it as is.

You can find the community firebase builder here.

You can find the build step on GitHub at

Instructions for using the custom step can be found in the but essentially can use the build step just like any of the community build steps:

git clone
cd firebase-cloud-builder
cloud container builds submit --config cloudbuild.yaml .
gcloud container images list --filter firebase

Once you’ve ran throught these steps you should be able to use the image “${PROJECT_ID}/firebase” as a build step in your own cloudbuild.yaml.

Encrypting Firebase Keys

Part of the magic of a cloudbuild.yaml is that it contains all the information you need to run a build in one convenient file you can commit to source control.

Most things in this file are great to share across the entire project — you wouldn’t want each member to build their own config from scratch — so it makes sense to commit this file to your repository.

It’s still a good idea to commit and publish build configurations that no individual is expected to run on their own — such as deploying a function to production — because it another avenue for knowledge sharing and collaboration between project members. Even it individuals don’t run a build on their own initiative it’s useful to know what’s going to happen so you can plan accordingly.

An issue arises when using the firebase builder to interact with a project in production — to deploy a site for example — one needs to include every bit if information needed to deploy including an authentication token.

Anyone with access to your firebase token can make the same changes that your build jobs can so it’s not a great idea to publish these tokens outside of where they’re strictly needed. The principle of least privilege applies here.

Luckily GCB has built in support for reading secrets encrypted using Google’s Key Management Service.

The GCB docs on the subject of encrypted key are very good but for the sake of complete & concrete examples here’s the section from my history with some annotations

First make sure gcloud and firebase are setup with the right projects. Second find the name of your container builder by running the following command:

gcloud projects get-iam-policy <PROJECT_ID>

The Service account will be in the form “{SERVICE_ACCOUNT}”

Then you can run the following commands:

gcloud kms keyrings create build-keyrrin --location=global
gcloud kms keys create deploy  --location=global --keyring=build-keyring --purpose=encryption
gcloud kms keys add-iam-policy-binding deploy \
  --location=global --keyring=build-keyring \ 
  --member=serviceAccount:{SERVICE-ACCOUNT} \
firebase login:ci --no-localhost
# Try to not actually commit this one to bash history, start the line with a space
 echo -n "<SECRET>" | gcloud kms encrypt --plaintext-file=- \
   --ciphertext-file=- --location=global --keyring=build-keyring \
   --key=deploy | base64 -w0

You then should be able to use the output of the last command to as the “SECRET_ENV” variable of your cloudbuild.yaml:

  - kmsKeyName: projects/neat-vent-139904/locations/global/keyRings/build-keyring/cryptoKeys/deploy

Finally, set the firebase step to load the FIREBASE_TOKEN from the secret store by setting the following on the build step


Complete cloudbuild.yaml

You can find a complete example in the cloudbuild.yaml for this site on GitHub

The important bits are:

# [...]
- name:
   - deploy
   - --project
   - site-ce15d
  - kmsKeyName: projects/neat-vent-139904/locations/global/keyRings/build-keyring/cryptoKeys/deploy
      FIREBASE_TOKEN: CiQAPi2Yo6ApJO4Ez0blG31ZUEk19xBdQEyICO3A1OCjpVvRbkASVgACg+475/JwBU5mjdpXY7X2crEooIQg/WIt2W87THf4StuyrbmKDihL7qpNedalIwwwCXTiqtIntHTGYj3YCZcMdigtvroTkvhZVFmqvT5Ljz5zkgjc

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