Example project for using Ruby on AWS Lambda via the Serverless Framework

Dockerfile

FROM lambci/lambda:build-ruby2.5

WORKDIR /var/task

CMD bundle install --path vendor/bundle

handler.rb

require 'aws-sdk-dynamodb'
require 'aws-sdk-s3'

DDB_ClIENT = Aws::DynamoDB::Client.new
S3_CLIENT = Aws::S3::Client.new

def process(event:, context:)
  event['Records'].each do |event_record|
    JSON.parse(event_record['Sns']['Message'])['Records'].each do |record|
      object = { bucket: record['s3']['bucket']['name'], key: record['s3']['object']['key'] }
      begin
        metadata = S3_CLIENT.head_object(object).metadata
      rescue Aws::S3::Errors::Forbidden
        metadata = {}
        puts "Error while getting #{ object.inspect }"
      end

      resp = DDB_ClIENT.put_item({
        item: {
          path: "#{ object[:bucket] }/#{ object[:key] }",
          metadata: metadata
        },
        table_name: ENV['TABLE_NAME'],
      })

      puts "Stored #{ metadata.inspect } in item #{ object[:bucket] }/#{ object[:key] }"
    end
  end
end

serverless.yml

service: log-s3-metadata

custom:
  bucket: your-bucket-name

provider:
  name: aws
  runtime: ruby2.5

  iamRoleStatements:
    - Effect: "Allow"
      Action:
        - "s3:ListBucket"
      Resource: "arn:aws:s3:::${self:custom.bucket}"
    - Effect: "Allow"
      Action:
        - "s3:HeadObject"
        - "s3:GetObject"
      Resource: "arn:aws:s3:::${self:custom.bucket}/*"
    - Effect: "Allow"
      Action:
        - "dynamodb:PutItem"
      Resource:
        Fn::GetAtt:
          - MetadataTable
          - Arn

functions:
  dynamo:
    handler: handler.process
    events:
      - sns: arn:aws:sns:us-east-1:XXX:s3-creations
    environment:
      TABLE_NAME: !Ref MetadataTable

# you can add CloudFormation resource templates here
resources:
  Resources:
    MetadataTable:
      Type: AWS::DynamoDB::Table
      Properties:
        BillingMode: PAY_PER_REQUEST
        AttributeDefinitions:
          - AttributeName: path
            AttributeType: S
        KeySchema:
          - AttributeName: path
            KeyType: HASH