Serverless Framework Ruby Sinatra API service backed by DynamoDB on AWS

Inspired and based off of aws-python-flask-api. Credit goes to @pgrzesik for the inspiration of this example and writing of this README that was shamelessly copied and updated to accomodated Ruby/Sinatra.

Anatomy of the template

This template configures a single function, api, which is responsible for handling all incoming requests thanks to configured http events. To learn more about http event configuration options, please refer to http event docs. As the events are configured in a way to accept all incoming requests, Sinatra framework is responsible for routing and handling requests internally. The implementation takes advantage of serverless-rack, which allows you to wrap Rack applications such as Sinatra apps, including bundling gem dependencies from the Gemfile. To learn more about serverless-rack, please refer to corresponding GitHub repository.

bin/bundle-compat is a small shim configured as custom.rack.bundlerBin: serverless-rack still shells out to the old bundle install --path ... --without ... invocation, but both flags were removed from modern Bundler (the version bundled with the ruby4.0 Lambda runtime) in favor of bundle config set --local. The shim translates one into the other and otherwise passes everything straight through to bundle.

Additionally, the template also handles provisioning of a DynamoDB database that is used for storing data about users. The Sinatra application exposes two endpoints, POST /users and GET /user/{userId}, which allow to create and retrieve users.

Packaging gems with native extensions: aws-sdk-dynamodb pulls in bigdecimal, which ships a compiled C extension. serverless-rack runs bundle install on whatever machine executes serverless package/deploy, so the extension gets compiled for that machine's platform. If you package from a host that isn't Linux/arm64 (e.g. a Mac, or a typical x86_64 CI runner, while this template deploys with provider.architecture: arm64), the gem that ends up in the deployment package won't load on Lambda, and the function will fail at init with Bundler::GemNotFound. Package/deploy from a matching Linux/arm64 environment instead — for example, running the deploy command inside a container based on public.ecr.aws/lambda/ruby:4.0 (with gcc/make installed for the native build) matches this template's Lambda runtime and architecture exactly.

Usage

Prerequisites

Ruby install of 4.0.*

Deployment

Install dependencies with:

npm install

and then perform deployment with:

serverless deploy

After running deploy, you should see output similar to:

Packaging Ruby Rack handler...
Backing up current bundle...
Packaging gem dependencies...
Bundle complete! 4 Gemfile dependencies, 15 gems now installed.
Gems in the group 'development' were not installed.
Restoring backed up bundle...
Packaging service...
Creating Stack...
Checking Stack create progress...
........
Stack create finished...
Uploading CloudFormation file to S3...
Uploading artifacts...
Uploading service aws-ruby-sinatra-dynamodb-api.zip file to S3 (4.86 MB)...
Validating template...
Updating Stack...
Checking Stack update progress...
....................................
Stack update finished...
Service Information
service: aws-ruby-sinatra-dynamodb-api
stage: dev
region: us-east-1
stack: aws-ruby-sinatra-dynamodb-api-dev
resources: 13
api keys:
  None
endpoints:
  ANY - https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/
  ANY - https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/{proxy+}
functions:
  api: aws-ruby-sinatra-dynamodb-api-dev-api
layers:
  None

Note: In current form, after deployment, your API is public and can be invoked by anyone. For production deployments, you might want to configure an authorizer. For details on how to do that, refer to http event docs.

Invocation

After successful deployment, you can create a new user by calling the corresponding endpoint:

curl --request POST 'https://xxxxxx.execute-api.us-east-1.amazonaws.com/dev/users' --header 'Content-Type: application/json' --data-raw '{"name": "John", "userId": "someUserId"}'

Which should result in the following response:

{"userId":"someUserId","name":"John"}

You can later retrieve the user by userId by calling the following endpoint:

curl https://xxxxxxx.execute-api.us-east-1.amazonaws.com/dev/users/someUserId

Which should result in the following response:

{"userId":"someUserId","name":"John"}

If you try to retrieve user that does not exist, you should receive the following response:

{"error":"Could not find user with provided \"userId\""}

Local development

Thanks to capabilities of serverless-rack, it is also possible to run your application locally.

bundle config set --local path vendor/bundle
bundle install
serverless rack serve

Additionally, you will need to emulate DynamoDB locally, which can be done by using the serverless-dynamodb plugin (the maintained fork of the now-archived serverless-dynamodb-local). In order to do that, execute the following commands:

serverless plugin install -n serverless-dynamodb
serverless dynamodb install

It will add the plugin to devDependencies in package.json file as well as to plugins section in serverless.yml. Additionally, it will also install DynamoDB locally.

You should also add the following config to custom section in serverless.yml:

custom:
  (...)
  dynamodb:
    start:
      migrate: true
    stages:
      - dev

We can take advantage of IS_OFFLINE environment variable set by serverless-rack plugin which will create a local DynamoDB client in api.rb:

client_options = if ENV['IS_OFFLINE']
                   {
                     region: 'localhost',
                     endpoint: 'http://localhost:8000',
                     credentials: Aws::Credentials.new(
                       'DEFAULT_ACCESS_KEY',
                       'DEFAULT_SECRET'
                     )
                   }
                 else
                   {}
                 end
dynamodb_client = Aws::DynamoDB::Client.new(client_options)

Now you can start DynamoDB local with the following command:

serverless dynamodb start

At this point, you can run your application locally with the following command:

serverless rack serve

For additional local development capabilities of serverless-rack and serverless-dynamodb plugins, please refer to corresponding GitHub repositories:

• https://github.com/logandk/serverless-rack
• https://github.com/raisenational/serverless-dynamodb