There’s a question often asked within development teams – what branch and/or commit ID is deployed on production (or staging) environment ? Firebase doesn’t let us answer that in any built-in or straightforward way. In some cases it might be a requirement to answer this question, primarily for services like firebase functions and firebase hosting.

We can always get the last deployment time and version identifier of firebase functions or go through the release history of firebase hosting in firebase console (project’s hosting section) but that won’t provide any git related information (commit hashes, branch names, etc.) because the firebase deployment processes has got nothing to do with the version control in use.

There may be a few ways to solve for the question given above, but my solution is to use a combination of:

• Environment configuration with functions.config to store the latest git branch and commit from whatever environment the deployment happens, and
• https functions to output the stored information at an endpoint that anybody from the team (or an internal tool) can quickly check.

Environment Config

Let’s first write a short and simple bash script that can resolve the required details like git commit ID and branch that we’d store in the functions environment configuration (and eventually show in the https endpoint):

#!/usr/bin/env bash

# Generate Deployment ID
BRANCH=$(git rev-parse --abbrev-ref HEAD)
COMMIT=$(git rev-parse HEAD)
DEPLOYMENT_ID="${BRANCH}-${COMMIT}"

# Set Deployment ID in config
firebase functions:config:set app.deployment_id="${DEPLOYMENT_ID}"

Save it in your functions source folder that contains index.js along with package.json. For me this path is functions/deploy.sh.

How will the execution of this script happen ? We’ll use firebase predeploy scripts for that.

Predeploy Hook

Just like Git hooks, firebase CLI tool also provides us with the functionality of attaching pre and post deploy hooks to the firebase deploy command. We can add this to our service (hosting, functions, storage, firestore, etc.) keys in our firebase.json configuration file.

Let’s say if I wanted this script to run before every deployment to the functions service, then this is how my firebase.json functions section would look like:

{
  // ...
  "functions": {
    "predeploy": "functions/deploy.sh",
    "source": "functions"
  }
  // ...
}

HTTPS Function

Finally we will use functions.https to create a firebase cloud function that will retrieve the deployment information stored in the environment configuration and send that as a response to HTTP requests that are sent by a browser or some code. Here’s how the function code would look like (exported in index.js):

const functions = require('firebase-functions');

exports.deploymentEndpoint = functions.https.onRequest(async (req, res) => {
  const deploymentId = functions.config().app?.deployment_id || 'Not Found';
  res.status(200).send(deploymentId);
});

To make sure that firebase hosting service forwards requests to this https function, add a rewrite entry into your firebase.json:

{
  "hosting": {
    "rewrites": [
      // ...
      {
        "source": "/deployment",
        "function": "deploymentEndpoint"
      },
      // ...
    ]
  }
  // ...
}

That’s all! Now all you gotta do is deploy your functions and hosting code with:

$ firebase deploy --only hosting,functions

The deployment will run the predeploy hook (our functions/deploy.sh) which resolves and sets the deployment commit and branch details into the functions configuration. After the deployment, you’ll have access to https://yoursite/deployment endpoint that will spit out the config value stored.

Bonus

We can always add the predeploy hook (deploy.sh in our case), to multiple service’s in the firebase.json. So we can add it to both functions and hosting services. In such cases the predeploy hook will run once for each service deployment, so in total twice for firebase deploy --only functions,hosting.

If you want to store separate deployment information for each service deployment, then you can pass separate arguments to the script in your predeploy field’s value and do an if/else based on that. In such a case, firebase.json would look something like this:

{
  // ...
  "hosting": {
    "predeploy": "functions/deploy.sh hosting",
    // ...
  },
  "functions": {
    "predeploy": "functions/deploy.sh functions",
    // ...
  }
}

And the deploy.sh would look something like this:

#!/usr/bin/env bash

if [ $# -gt 0 ]; then
  # Generate Deployment information

  # Set Deployment ID in config
  if [ "$1" = "hosting" ]; then
    # Set deployment information in app.hosting_deployment_id
  fi

  if [ "$1" = "functions" ]; then
    # Set deployment information in app.functions_deployment_id
  fi

else
  echo "ERROR: First argument missing. Accepted values: hosting, functions"
  exit 1
fi