use stage to manage environment variables in Serverless framework

Serverless framework is a fantastic framework to simplified your serverless management. Most of the time, we have some configurations which are different among different environments. Let’s say how could we achieve this with Serverless framework. Including manage tests in Jest.

1. Overview

The application should be environment agnostic. So we manage all the values in the environment variables and use it in your lambda.

1. Separate environment variables in their own .json file.
2. Load the above .json file conditionally in your serverless.yml
3. Add all the environment variables from the loaded .json file

For the following sections, we will setup two environments, dev and prod, this setup is very scalable, adding more env like uat is just a matter of adding new uat.json.

2. Create .json file for your environment variables

This is the ./src/config/dev.json

{
  "SECRET": "1234"
}

This is the ./src/config/prod.json

{
  "SECRET": "5678"
}

3. Setup your serverless.yml

custom:
  stage: ${opt:stage, 'dev'}
  config: file(./src/config/${self:custom.stage}.json)

You will add this at the top level. Let’s digest it line by line.

• We first created a custom section. This is how we DIY the settings.
• stage: ${opt:stage, 'dev'}: Means we will add a stage under custom, we would like to get the value from the CLI option --stage BLAHBLAH, if no value from the CLI option, the fallback value will be dev.
• finally, we created config, and it is a file(), the source of the file is ./src/config/${self:custom.stage}.json, self:custom.stage refers to the current stage, which will be dynamic. Which means we will load dev.json or prod.json conditionally according to the CLI option or fallback value.

4. Map all the environment variables

provider:
  environment:
    SECRET: ${${self:custom.config}:SECRET}

After loading the file, the rest is as easy as map them to the provider section of your serverless.yml. Here, we created a SECRET, the value is from the SECRET property in the .json file.

In your lambda, process.env.SECRET will give you the value. And the value will be dynamic according to the current stage.

The values under provider section will be shared across all functions. If you want a function-specific environment variable, you can add it under the very function that you want to configure.

5. What about unit test

I use Jest to test, the problem is when we run the tests via jest, we lose the support of the framework, so all our previous setup is not working anymore.

This is easy to solve. At the top of your test.

import config from "../config/dev.json";
process.env = config;

You can use test.json if you have a different setup. It’s very easy to understand, we import this json, and manually assign them to the process.env.

6. End

Hope it helps.

Thanks for reading!

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