Working with layers for Ruby Lambda functions

Create a Gemfile to specify the pure Ruby gems you want to include in your layer:

source 'https://rubygems.org'

gem 'tzinfo'

Install the gems to vendor/bundle directory using Bundler:

bundle config set --local path vendor/bundle
bundle install

Copy the installed gems to the directory structure that Lambda requires ruby/gems/3.4.0):

mkdir -p ruby/gems/3.4.0
cp -r vendor/bundle/ruby/3.4.0*/* ruby/gems/3.4.0/

Zip the layer content:

The directory structure of your .zip file should look like this:

ruby/              
└── gems/
    └── 3.4.0/
        ├── gems/
        │   ├── concurrent-ruby-1.3.5/
        │   └── tzinfo-2.0.6/
        ├── specifications/
        ├── cache/
        ├── build_info/
        └── (other bundler directories)

Create a Gemfile.

source 'https://rubygems.org'

gem 'nokogiri'
gem 'httparty'

Use Docker to build the gems in a Linux environment that is compatible with Lambda. Specify an Amazon base image in your Dockerfile:

FROM public.ecr.aws/lambda/ruby:3.4

# Copy Gemfile
COPY Gemfile ./

# Install system dependencies for native extensions
RUN dnf update -y && \
    dnf install -y gcc gcc-c++ make

# Configure bundler and install gems
RUN bundle config set --local path vendor/bundle && \
    bundle install

# Create the layer structure
RUN mkdir -p ruby/gems/3.4.0 && \
    cp -r vendor/bundle/ruby/3.4.0*/* ruby/gems/3.4.0/

# Create the layer zip file
RUN zip -r layer.zip ruby/

Build the image and extract the layer:

docker build -t ruby-layer-builder .
docker run --rm -v $(pwd):/output --entrypoint cp ruby-layer-builder layer.zip /output/

This builds the gems in the correct Linux environment and copies the layer.zip file to your local directory. The directory structure of your .zip file should look like this:

ruby/
└── gems/
    └── 3.4.0/
        ├── gems/
        │   ├── bigdecimal-3.2.2/
        │   ├── csv-3.3.5/
        │   ├── httparty-0.23.1/
        │   ├── mini_mime-1.1.5/
        │   ├── multi_xml-0.7.2/
        │   ├── nokogiri-1.18.8-x86_64-linux-gnu/
        │   └── racc-1.8.1/
        ├── build_info/
        ├── cache/
        ├── specifications/
        └── (other bundler directories)

Create the required directory structure for your layer:

mkdir -p ruby/lib

Create your Ruby modules in the ruby/lib directory. The following example module validates orders by confirming that they contain the required information.

require 'json'

module OrderValidator
  class ValidationError < StandardError; end

  def self.validate_order(order_data)
    # Validates an order and returns formatted data
    required_fields = %w[product_id quantity]
    
    # Check required fields
    missing_fields = required_fields.reject { |field| order_data.key?(field) }
    unless missing_fields.empty?
      raise ValidationError, "Missing required fields: #{missing_fields.join(', ')}"
    end
    
    # Validate quantity
    quantity = order_data['quantity']
    unless quantity.is_a?(Integer) && quantity > 0
      raise ValidationError, 'Quantity must be a positive integer'
    end
    
    # Format and return the validated data
    {
      'product_id' => order_data['product_id'].to_s,
      'quantity' => quantity,
      'shipping_priority' => order_data.fetch('priority', 'standard')
    }
  end

  def self.format_response(status_code, body)
    # Formats the API response
    {
      statusCode: status_code,
      body: JSON.generate(body)
    }
  end
end

Zip the layer content:

The directory structure of your .zip file should look like this:

ruby/              
└── lib/
    └── order_validator.rb

In your function, require and use the modules. You must require each gem individually in your function code. You can't use bundler/setup or Bundler.require. For more information, see Using gems from layers in a function. Example:

require 'json'
require 'order_validator'

def lambda_handler(event:, context:)
  begin
    # Parse the order data from the event body
    order_data = JSON.parse(event['body'] || '{}')
    
    # Validate and format the order
    validated_order = OrderValidator.validate_order(order_data)
    
    OrderValidator.format_response(200, {
      message: 'Order validated successfully',
      order: validated_order
    })
  rescue OrderValidator::ValidationError => e
    OrderValidator.format_response(400, {
      error: e.message
    })
  rescue => e
    OrderValidator.format_response(500, {
      error: 'Internal server error'
    })
  end
end

You can use the following test event to invoke the function:

{
    "body": "{\"product_id\": \"ABC123\", \"quantity\": 2, \"priority\": \"express\"}"
}

Expected response:

{
  "statusCode": 200,
  "body": "{\"message\":\"Order validated successfully\",\"order\":{\"product_id\":\"ABC123\",\"quantity\":2,\"shipping_priority\":\"express\"}}"
}