Write your AWS Lambda function handlers using a Rake-like declarative syntax:

# ./lambda_function.rb
require "yake"

handler :lambda_handler do |event|
  # Your code here
end

# Handler signature: `lambda_function.lambda_handler`

You can even declare Sinatra-like API Gateway routes for a main entrypoint:

# ./lambda_function.rb
require "yake/api"

header "content-type" => "application/json"

get "/fizz" do |handler|
  respond 200, { ok: true }.to_json
end

handler :lambda_handler do |event|
  route event
rescue => err
  respond 500, { message: err.message }.to_json
end

# Handler signature: `lambda_function.lambda_handler`

Add this line to your application's Gemfile:

gem "yake"

And then execute:

bundle install

Or install it yourself as:

gem install yake

"λ" + Rake, but "λ" is hard to type and I think "y" looks like a funny little upside-down-and-backwards Lambda symbol.

So why use yake for your Lambda functions?

yake does not depend on any other gems, using the Ruby stdlib only. This helps keep your Lambda packages slim & speedy.

By default, the handler function wraps its block in log lines formatted to match the style of Amazon's native Lambda logs sent to CloudWatch. Each invocation of the handler will log both the input event and the returned value, prefixed with the ID of the request:

START RequestId: 149c500f-028a-4b57-8977-0ef568cf8caf Version: $LATEST
INFO RequestId: 149c500f-028a-4b57-8977-0ef568cf8caf EVENT { … }
…
INFO RequestId: 149c500f-028a-4b57-8977-0ef568cf8caf RETURN { … }
END RequestId: 149c500f-028a-4b57-8977-0ef568cf8caf
REPORT RequestId: 149c500f-028a-4b57-8977-0ef568cf8caf	Duration: 43.97 ms	Billed Duration: 44 ms	Memory Size: 128 MB	Max Memory Used: 77 MB

Logging the request ID in this way makes gathering logs lines for a particular execution in CloudWatch much easier.

This feature can be disabled by adding a declaration in your handler file:

logging :off

A common use of Lambda functions is as a proxy for API Gateway. Oftentimes users will deploy a single Lambda function to handle all requests coming from API Gateway.

Requiring the yake/api module will add the API-specific DSL into your handler.

Define API routes using Sinatra-like syntax

delete "/…" do |event|
  # Handle 'DELETE /…' route key events
end

get "/…" do |event|
  # Handle 'GET /…' route key events
end

head "/…" do |event|
  # Handle 'HEAD /…' route key events
end

options "/…" do |event|
  # Handle 'OPTIONS /…' route key events
end

patch "/…" do |event|
  # Handle 'PATCH /…' route key events
end

post "/…" do |event|
  # Handle 'POST /…' route key events
end

put "/…" do |event|
  # Handle 'PUT /…' route key events
end

Helper methods are also made available to help produce a response for API Gateway:

Set a default header for ALL responses:

header "content-type" => "application/json; charset=utf-8"
header "x-custom-header" => "fizz"

Produce an API Gateway-style response object:

respond 200, { ok: true }.to_json, "x-extra-header" => "buzz"
# {
#   "statusCode" => 200,
#   "body" => '{"ok":true}',
#   "headers" => { "x-extra-header" => "fizz" }
# }

Route an event to one of the declared routes:

handler :lambda_handler do |event|
  route event
rescue Yake::UndeclaredRoute => err
  respond 404, { message: err.message }.to_json
rescue => err
  respond 500 { message: err.message }.to_json
end

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/amancevice/yake.

The gem is available as open source under the terms of the MIT License.