Deploy a new Rails app to AWS Lambda using Lamby

rails_lamby_notes.md

Rails => Lambda

These are my notes from deploying a boilerplate Rails app to AWS Lambda (yeah, you read that right) using Lamby. Basically this is me going through the Quick Start guide.

• https://aws.amazon.com/lambda/
• https://lamby.custominktech.com
• https://lamby.custominktech.com/docs/quick_start

Questions/comments: https://twitter.com/heyjoshwood

Notes

• Generate the initial Rails app:

  brew install awscli jq
  brew tap aws/tap
  brew install aws-sam-cli
  
  asdf shell ruby 2.7.1
  
  gem install rails -N
  
  rails new lamby_rails \
    --skip-action-mailer --skip-action-mailbox --skip-action-text \
    --skip-active-record --skip-active-storage --skip-puma \
    --skip-action-cable --skip-spring --skip-listen --skip-turbolinks \
    --skip-system-test --skip-bootsnap
  
  cd lamby_rails
  
  git add .
  git commit -m 'initial'

• Edit app/controllers/application_controller.rb:

  class ApplicationController < ActionController::Base
  +  def index
  +    render html: "<h1>Hello Lamby</h1>".html_safe
  +  end
  end

  Edit config/routes.rb:

  Rails.application.routes.draw do
  +  root to: "application#index"
  end

• Save progress:

  git add -p
  git commit -m 'hello lamby'

• Install lamby gems:

  bundle add lamby aws-sdk-ssm

• Edit Gemfile:

  - gem "lamby", "~> 2.0"
  + gem "lamby", "~> 2.0", require: false

• Finish installing lamby:

  ./bin/rake -r lamby lamby:install
  
  git add -p
  git status
  git add .
  git commit -m 'install lamby'

• I set up my AWS credentials here:

  # ~/.aws/credentials
  [lamby_rails]
  aws_access_key_id = VALUE
  aws_secret_access_key = SECRET_VALUE
  

• And the region config here:

  # ~/.aws/config
  [lamby_rails]
  output = json
  region = us-west-1
  

• I set my AWS_PROFILE using direnv. Edit .envrc:

  export AWS_PROFILE=lamby_rails
  

  then run:

  direnv allow

• Configure SSM w/ Rails master key:

  aws ssm put-parameter \
    --name "/config/lamby_rails/env/RAILS_MASTER_KEY" \
    --type "SecureString" \
    --value $(cat config/master.key)

• Edit app.rb and add this line right after require 'lamby':

  ENV['RAILS_MASTER_KEY'] =
    Lamby::SsmParameterStore.get!('/config/lamby_rails/env/RAILS_MASTER_KEY')

• Edit template.yaml CloudFormation/SAM file by adding this to the Properties section of your RailsFunction. This addition allows your Lambda's runtime policy to read configs from SSM Parameter store (see full template.yml attached):

  Policies:
    - Version: "2012-10-17"
      Statement:
        - Effect: Allow
          Action:
            - ssm:GetParameter
            - ssm:GetParameters
            - ssm:GetParametersByPath
            - ssm:GetParameterHistory
          Resource:
            - !Sub arn:aws:ssm:${AWS::Region}:${AWS::AccountId}:parameter/config/lamby_rails/*
  

• Save progress:

  git add -p
  git commit -m 'configure lamby'

• Edit .envrc (change the bucket name):

  export CLOUDFORMATION_BUCKET=lamby-rails-josh
  export AWS_DEFAULT_REGION=us-west-1
  

  don't forget:

  direnv allow

• Now run:

  aws s3 mb "s3://$CLOUDFORMATION_BUCKET"
  
  ./bin/deploy

• This uses Docker to bake the Rails app Lambda function. That can take a long time on macOS. Go get some coffee or tea. :)

  $ time ./bin/deploy
  
  Successfully created/updated stack - lambyrails-production-us-west-1 in None
  ./bin/deploy  17.45s user 9.86s system 5% cpu 9:04.13 total

  (that's the build/deploy time on an 8-core MacBook Pro 🤔)

template.yml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: LambyRails Lambda (HTTP API)

Parameters:

  RailsEnv:
    Type: String
    Default: production
    AllowedValues:
      - staging
      - production

Resources:

  RailsFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: .
      Handler: app.handler
      Runtime: ruby2.7
      MemorySize: 512
      Timeout: 30
      Environment:
        Variables:
          RAILS_ENV: !Ref RailsEnv
      FunctionName: !Join [ '', [ 'LambyRails-', !Ref RailsEnv, '-', !Ref 'AWS::Region' ] ]
      Events:
        RailsApiProxy:
          Type: HttpApi
          Properties:
            ApiId: !Ref RailsApi
      AutoPublishAlias: live
      Policies:
        - Version: "2012-10-17"
          Statement:
            - Effect: Allow
              Action:
                - ssm:GetParameter
                - ssm:GetParameters
                - ssm:GetParametersByPath
                - ssm:GetParameterHistory
              Resource:
                - !Sub arn:aws:ssm:${AWS::Region}:${AWS::AccountId}:parameter/config/lamby_rails/*

  RailsApi:
    Type: AWS::Serverless::HttpApi
    Properties:
      StageName: !Ref RailsEnv

Outputs:

  RailsApiUrl:
    Description: API Gateway Endpoint
    Value: !Sub "https://${RailsApi}.execute-api.${AWS::Region}.amazonaws.com/${RailsEnv}/"

  RailsFunctionArn:
    Description: Lambda ARN
    Value: !GetAtt RailsFunction.Arn