ActionCable in Lambda

[mtrolle]

Hi,

Do you have any experience in getting ActionCable up and running via Lambda? I personally don't rely on this yet but I'm curious as I wanna start using the Hotwire gems and Turbo stream especially.

I would probably have to look more into AWS Api Gateway for Websocket to be successful as it definitely won't work out of the box on the HTTP api directly (at least not for my initial testing).

I'm unsure if I wanna pursue this, but just curious if there's anyone out there who's done it already.

[metaskills]

It should be possible. On my list of things to look into since I want to do a post on how to use Lamby with Hotwire.

[metaskills]

#74

[atwoodjw]

I think this would be super interesting.

I got as far as creating the CF resources and adapter before I realized how tightly coupled Action Cable is to the WebSocket protocol. Sharing what I have so far, in case anyone's inclined to pick it up from here.

...

RailsConnectionsTable:
  Type: AWS::Serverless::SimpleTable
  Properties:
    PrimaryKey:
      Name: connectionId
      Type: String
    ProvisionedThroughput:
      ReadCapacityUnits: 5
      WriteCapacityUnits: 5
    SSESpecification:
      SSEEnabled: True
    TableName: ...

RailsWsDomainName:
  Type: AWS::ApiGatewayV2::DomainName
  Properties:
    DomainName: !Sub cable.${Domain}
    DomainNameConfigurations:
      - CertificateArn: !Ref CertificateArn
        EndpointType: REGIONAL
        SecurityPolicy: TLS_1_2

RailsWsApiMapping:
  Type: AWS::ApiGatewayV2::ApiMapping
  DependsOn: RailsWsDomainName
  Properties:
    ApiId: !Ref RailsWsApi
    DomainName: !Sub cable.${Domain}
    Stage: !Ref RailsEnv

RailsWsRecordSet:
  Type: AWS::Route53::RecordSetGroup
  DependsOn: RailsWsApiMapping
  Properties:
    HostedZoneId: !Ref HostedZoneId
    RecordSets:
      - Name: !Sub cable.${Domain}
        Type: A
        AliasTarget:
          HostedZoneId: !GetAtt RailsWsDomainName.RegionalHostedZoneId
          DNSName: !GetAtt RailsWsDomainName.RegionalDomainName
          EvaluateTargetHealth: false

RailsWsApi:
  Type: AWS::ApiGatewayV2::Api
  Properties:
    Name: !Sub cable-${RailsEnv}
    ProtocolType: WEBSOCKET
    RouteSelectionExpression: "$request.body.action"

RailsWsLambdaPermission:
  Type: AWS::Lambda::Permission
  DependsOn:
    - RailsWsApi
  Properties:
    Action: lambda:InvokeFunction
    FunctionName: !Ref RailsLambda
    Principal: apigateway.amazonaws.com

RailsWsIntegration:
  Type: AWS::ApiGatewayV2::Integration
  Properties:
    ApiId: !Ref RailsWsApi
    IntegrationType: AWS_PROXY
    IntegrationUri:
      Fn::Sub:
        arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${RailsLambda.Arn}/invocations
    PayloadFormatVersion: 1.0

RailsWsConnectRoute:
  Type: AWS::ApiGatewayV2::Route
  Properties:
    ApiId: !Ref RailsWsApi
    RouteKey: $connect
    Target: !Join
      - '/'
      - - 'integrations'
        - !Ref RailsWsIntegration

RailsWsDisconnectRoute:
  Type: AWS::ApiGatewayV2::Route
  Properties:
    ApiId: !Ref RailsWsApi
    RouteKey: $disconnect
    Target: !Join
      - '/'
      - - 'integrations'
        - !Ref RailsWsIntegration

RailsWsDefaultRoute:
  Type: AWS::ApiGatewayV2::Route
  Properties:
    ApiId: !Ref RailsWsApi
    RouteKey: $default
    Target: !Join
      - '/'
      - - 'integrations'
        - !Ref RailsWsIntegration

RailsWsDeployment:
  Type: AWS::ApiGatewayV2::Deployment
  DependsOn:
    - RailsWsConnectRoute
    - RailsWsDisconnectRoute
    - RailsWsDefaultRoute
  Properties:
    ApiId: !Ref RailsWsApi

RailsWsStage:
  Type: AWS::ApiGatewayV2::Stage
  Properties:
    ApiId: !Ref RailsWsApi
    AutoDeploy: true
    StageName: !Ref RailsEnv

# frozen_string_literal: true

# https://github.com/aws-samples/simple-websockets-chat-app

module ActionCable
  module SubscriptionAdapter
    class APIGateway < Base
      def initialize(*)
        super

        @api_gateway_management_api = Aws::ApiGatewayManagementApi::Client.new(
          {
            endpoint: @server.config.cable[:endpoint]
          }
        )

        @dynamo_db = Aws::DynamoDB::Client.new

        @table_name = @server.config.cable[:table_name]
      end

      def broadcast(channel, payload)
        connection_ids = @dynamo_db.scan(
          {
            projection_expression: 'connectionId',
            table_name: @table_name
          }
        ).items.map do |item|
          item['connectionId']
        end

        connection_ids.each do |connection_id|
          @api_gateway_management_api.post_to_connection(
            {
              data: payload,
              connection_id: connection_id
            }
          )
        rescue Aws::ApiGatewayManagementApi::Errors::NotFoundException
          @dynamo_db.delete_item(
            {
              key: {
                connectionId: channel
              },
              table_name: @table_name
            }
          )
        end
      end

      def subscribe(channel, callback)
        @dynamo_db.put_item(
          {
            item: {
              connectionId: channel
            },
            table_name: @table_name
          }
        )

        callback.call
      end

      def unsubscribe(channel, callback)
        @dynamo_db.delete_item(
          {
            key: {
              connectionId: channel
            },
            table_name: @table_name
          }
        )

        callback.call
      end

      def shutdown; end
    end
  end
end