netlify-plugin-inline-functions-env

Inline process.env.X in netlify functions with netlify build time environment variables.

Why

When we talk about environment variable values for a netlify function, it is important to understand that there're two possible context.

Build time

This is when netlify builds your site. The following environment variables would be available at build time:

• Environment Variables you set at Netlify UI
• Readonly Environment Variables set by Netlify including build/git metadata
• Deploy Context Environment Variables you set in netlify.toml within [context.xxx.environment] section
• Environment Variables set by other Netlify build plugins such as contextual env plugin

Runtime

This is when your function code is evaluated when a request was received. The following environment variables would be available at runtime:

• Environment Variables you set at Netlify UI

Problem

You may have noticed that the available environment variables at Runtime is only a subset of that in build time.

That is a common source of confusion for many people, see discussions over here.

This plugin was built to mitigate this issue by inlining the build time environment variable values as part of your code, so that you can consider build time environment variables magically become available for runtime!

With the original function source file

function handler(event, context) {
  return {
    statusCode: 200,
    body: JSON.stringify({
      CONTEXT: process.env.CONTEXT
    })
  };
};

module.exports = { handler };

The plugin will produce the inlined function source file

function handler(event, context) {
  return {
    statusCode: 200,
    body: JSON.stringify({
      CONTEXT: "deploy-preview"    <---------- replaced with build time env var values
    })
  };
};

module.exports = { handler };

Caveats

The plugin wouldn't replace more dynamic code like the following ones

console.log(process.env);          <-------- no concrete values, won't be replaced with an object

function getKey(key) {
  return process.env[key];         <-------- rely on runtime value so won't be replaced
}

So you may have to intentionlly convert the above code into something like process.env.X so it will be inlined.

Install

To install, add the following lines to your netlify.toml file:

[[plugins]]
package = "netlify-plugin-inline-functions-env"

More Options

Debugging

You can turn on verbose for debugging purpose by providing plugin inputs.

[[plugins]]
package = "netlify-plugin-inline-functions-env"
  [plugins.inputs]
  verbose = "true"

Be careful with verbose mode, as it will print the files with the replaced env variables

Configuring build event

If you are using TypeScript, or processing your code in other ways you may want to choose onBuild

[[plugins]]
package = "netlify-plugin-inline-functions-env"
  [plugins.inputs]
  buildEvent = "onBuild"

Default value is onPreBuild. It's also been tested to work with onBuild The values for buildEvent can be found here

Conditional Transformation

If you are using libraries such as dotenv-defaults, you may want to limit or skip the transformation for certain environment variables.

[[plugins]]
package = "netlify-plugin-inline-functions-env"
  [plugins.inputs]
  exclude = ["DO_NOT_TRANSFORM_ME", "DO_NOT_TRANSFORM_ME_2"]

[[plugins]]
package = "netlify-plugin-inline-functions-env"
  [plugins.inputs]
  include = ["ONLY_TRANSFORM_ME", "ONLY_TRANSFORM_ME_2"]

Gotchas

1. The [[plugins]] line is required for each plugin, even if you have other plugins in your netlify.toml file already.

2. This plugin only replaces variables in the functions directory. Files outside the directory won't be modified.

3. Also please add netlify-plugin-inline-functions-env to your dev dependencies by yarn install --dev netlify-plugin-inline-functions-env or npm install --save-dev netlify-plugin-inline-functions-env.