Static Env ServerlessFramework Plugin

This plugin is is intended for use with Lambda@Edge to replace process.env and other similar mechanisms referencing environment variables with static values so that environment specific configuration can be used in Lambda@Edge (which does not support environment variables).

This is forked from serverless-plugin-embedded-env-in-code with as it takes a different solution to the same problem of providing environment variables to Lambda@Edge.

In summary, what this does is take all environment variables specified in the serverless.yml in provider.environment or function.environment and packages them into the deployment zip so they become defaults if the environment variables defined when the function is executed. Practically speaking this means any environment variables specified in provider.environment or function.environment are available to Lambda@Edge functions the same way as they would to a normal lambda. The key difference being a redeployment is required to update the values.

Configuration

Environment variables and their values are configured as normal, either in the top level provider.environment or function.engironment

When the function is packaged for deployment the values will be embedded in the package so that they are present in process.env as normal. Note that any environment variables actually set in the environment will take precedence, these are packaged as defaults only.

By default, any function with a cloudFront event trigger will have it's environment variables embedded during packaging.

A function can explicitly opt in or out of this behavior by specifying the boolean includeStaticEnv in the function definition.

Example

The below serverless.yml shows the various usages

service:
  name: static-env-example

provider:
  name: aws
  runtime: nodejs12.x
  stage: ${opt:stage, 'development'}
  region: 'us-east-1'

  # These environment variables will be made available to all function and included
  # where static environment is embedded
  environment:
    SHARED_ENVIRONMENT_VAR1: 'value1'
    SHARED_ENVIRONMENT_VAR2: 'value2'

plugins:
  - serverless-plugin-static-env

functions:
  edgeFunctionWithStaticEnv:
    handler: dist/endpoints/edgeFunctionWithStaticEnv.handler
    environment:
      FUNCTION_SPECIFIC_ENVIRONMENT_VAR1: 'value3'
      FUNCTION_SPECIFIC_ENVIRONMENT_VAR2: 'value4'
    # includeStaticEnv: true # this will have static env by default because it includes a
                             # cloudFront event trigger. If this was set to false it would
                             # not have a static env even though it has a cloudFront trigger
                             #
                             # Without a cloudFront trigger this would have to be explicitly
                             # set to true to opt in to embedding the static environment
    events:
      - cloudFront:
          eventType: viewer-response
          origin: s3://bucketname.s3.amazonaws.com/files

How it Works

For each function an additional -env.js file is generated with the static environment. E.g. with the example configuration above the file dist/endpoints/edgeFunctionWithStaticEnv-env.js would be generated with the following content

process.env["SHARED_ENVIRONMENT_VAR1"] = process.env["SHARED_ENVIRONMENT_VAR1"] == null ? "value1": process.env["SHARED_ENVIRONMENT_VAR1"];
process.env["SHARED_ENVIRONMENT_VAR2"] = process.env["SHARED_ENVIRONMENT_VAR2"] == null ? "value2": process.env["SHARED_ENVIRONMENT_VAR2"];
process.env["FUNCTION_SPECIFIC_ENVIRONMENT_VAR1"] = process.env["FUNCTION_SPECIFIC_ENVIRONMENT_VAR1"] == null ? "value3": process.env["FUNCTION_SPECIFIC_ENVIRONMENT_VAR1"];
process.env["FUNCTION_SPECIFIC_ENVIRONMENT_VAR2"] = process.env["FUNCTION_SPECIFIC_ENVIRONMENT_VAR2"] == null ? "value4": process.env["FUNCTION_SPECIFIC_ENVIRONMENT_VAR2"];

The file dist/endpoints/edgeFunctionWithStaticEnv.js would also be updated to require dist/endpoints/edgeFunctionWithStaticEnv-env.js as it's first action ensuring that these variables are present before any other required code is executed.