Lately I've been using Serverless on a variety of projects, including personal ones.

• Serverless

Put simply, it's a tool that lets you efficiently create and update resources of the kind known as FaaS (Function as a Service), like AWS Lambda or Google Cloud Functions.

Apex and AWS's own SAM CLI could also be considered similar tools.

• AWS Lambda
• Google Cloud Functions
• Apex
• SAM CLI

Background

With Serverless, you can deploy with a single command, so there's no need to bundle code and dependencies before uploading. That makes it easy to deploy from your local machine or run it from CI.

• serverless cli: deploy

If the deployment flow were completely unified, there'd be no issue, but sometimes you normally deploy from CI yet want to deploy a small fix locally, or you want to roll back after a failed deploy.

In situations like that, I'd occasionally find myself wondering "wait, what state is this in right now?", so I wanted an easy way to attach version information.

So I made it read the information from package.json and add it at deploy time.

What I did

I had been managing additional information in a separate YAML file, but I recently learned that JSON files can be loaded too.

• Reference Variables in Other Files

If you've installed serverless under your project via npm or yarn, you should have a package.json, so let's load its version field as additional info.

As an example, suppose a directory contains the source code along with package.json and serverless.yml.

package.json has a version of 1.0.0.

{
  ...
  "version": "1.0.0",
  ...
}

To load this in serverless.yml, do the following.

custom:
  package: ${file(./package.json)} # Load package.json

With this in place, writing ${self:custom.package.version} lets you attach the version info of 1.0.0 at Serverless deploy time, so I passed it into a VERSION environment variable.

provider:
  ...
  environment:
    VERSION: ${self:custom.package.version} # Assign to the VERSION environment variable

This assumes you keep the version info updated appropriately, but now I can easily check which state is currently deployed.