serverless-ruby-package

Teaches the serverless framework how to package ruby services and their gem dependencies.

By default, serverless will package all files in your ruby service project. That includes test files, node_modules, readmes, etc. You don't need any of those files to execute your function - they just increase the size of the package and slow down updates. In most cases, it also won't include any rubygems that your function depends on, so the function will not work once it is deployed.

This plugin solves those problems in a couple ways. First, it excludes all files by default, forcing you to whitelist the files needed by your function (using the package/includes key in serverless.yml). Second, it automatically packages the gems from your default bundler group -- skipping gems from any custom groups, like development or test. Sometimes gems themselves will install their own test files - those will also be excluded from the package.

It also handles cross-compiling any gems with native extensions. For example, if you are developing your service on macOS, any gems with native extensions will be compiled locally for macOS. But to deploy to a provider like AWS Lambda, the gems need to be compiled for linux. The plugin will automatically detect this situation and build the extensions for linux using a local docker container. You only need to have docker installed with the daemon running.

Usage

The plugin will make it easier to work with rubygems in your serverless project, but it requires your project to follow some conventions:

Add the plugin

npm install --save-dev serverless-ruby-package

Add the plugin to your serverless.yml file:

plugins:
  - serverless-ruby-package

You must use bundler in standalone mode, with the path vendor/bundle:

bundle install --standalone --path vendor/bundle

Add the following lines to the top of your service handler file:

load "vendor/bundle/bundler/setup.rb"

The plugin will force the serverless packaging step to exclude all files by default. You need to explicitly add your service handler file to serverless.yml:

package:
  include:
    - handler.rb

(optional) If your service is implemented across multiple ruby files, it is recommended that you keep your handler file in the root, and the rest of the files in a lib/ directory. You can make them available to your handler by adding the following line to the top of your handler:

# handler.rb 
load "vendor/bundle/bundler/setup.rb"
$LOAD_PATH.unshift(File.expand_path("lib", __dir__))

You will also need to edit your serverless.yml package settings to include those files:

package:
  include:
    - handler.rb
    - lib/**

Verify

Build your package to confirm it is being built as expected:

serverless package

Note - if you have gems with native extensions, and are not developing on linux, make sure have docker installed and running. The first time you package may take a really long time as the docker image is downloaded. Future packaging will be much faster.

That will create the package that is uploaded during a serverless deploy, but keep it around so you can examine it. You can use the following command to verify it only includes the files you expect:

unzip -l .serverless/<servicename>.zip

Configuration

By default, if any gems have native extensions, they will be compiled for the AWS Lambda Linux using Docker.

You can override the default behavior by adding to your serverless.yml file:

custom:
  rubyPackage:
    alwaysCrossCompileExtensions: false

You can also override this behavior using environment variable. If you set the environment variable, it will have precedence over the serverless.yml file:

CROSS_COMPILE_EXTENSIONS=false serverless package

By default, native extensions will be built using the lambci/lambda:build-ruby2.5 docker image, which should accurately reflect the AWS Lambda ruby environment. To use a different image, override it in your serverless.yml file:

custom:
  rubyPackage:
    dockerImage: lambci/lambda:build-ruby2.7

Development

To work on this plugin, you should first run the following in your local directory:

./dev_setup.sh          # configures the demo service project needed by the tests

yarn test               # run the automated test suite

./integration_test.sh   # run serverless package on the demo project and observe the results

Troubleshooting the demo_service

Make sure the version of bundler specified in the demo_service Gemfile.lock is compatible with the version installed in the lambci/lambda:build-ruby2.5 image.
Make sure you can invoke the function n in the docker image:

./invoke-service.sh

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