Graphql Lambda Subscriptions

Amazon Lambda Powered GraphQL Subscriptions. This is an Amazon Lambda Serverless equivalent to graphql-ws. It follows the graphql-ws prototcol. It is tested with the Architect Sandbox against graphql-ws directly and run in production today. For many applications graphql-lambda-subscriptions should do what graphql-ws does for you today without having to run a server. This started as fork of subscriptionless another library with similar goals.

As subscriptionless's tagline goes;

Have all the functionality of GraphQL subscriptions on a stateful server without the cost.

Why a fork?

I had different requirements and needed more features. This project wouldn't exist without subscriptionless and you should totally check it out.

Features

• Only needs DynamoDB, API Gateway and Lambda (no app sync or other managed graphql platform required, can use step functions for ping/pong support)
• Provides a Pub/Sub system to broadcast events to subscriptions
• Provides hooks for the full lifecycle of a subscription
• Type compatible with GraphQL and nexus.js
• Optional Logging

Quick Start

Since there are many ways to deploy to amazon lambda I'm going to have to get opinionated in the quick start and pick Architect. graphql-lambda-subscriptions should work on Lambda regardless of your deployment and packaging framework. Take a look at the arc-basic-events mock used for integration testing for an example of using it with Architect.

API Docs

Can be found in our docs folder. You'll want to start with makeServer() and subscribe().

Setup

Create a graphql-lambda-subscriptions server

import { makeServer } from 'graphql-lambda-subscriptions'

// define a schema and create a configured DynamoDB instance from aws-sdk
// and make a schema with resolvers (maybe look at) '@graphql-tools/schema

const subscriptionServer = makeServer({
  dynamodb,
  schema,
})

Export the handler

export const handler = subscriptionServer.webSocketHandler

Configure API Gateway

Set up API Gateway to route WebSocket events to the exported handler.

@app
basic-events

@ws

functions:
  websocket:
    name: my-subscription-lambda
    handler: ./handler.handler
    events:
      - websocket:
          route: $connect
      - websocket:
          route: $disconnect
      - websocket:
          route: $default

Create DynamoDB tables for state

In-flight connections and subscriptions need to be persisted.

Changing DynamoDB table names

Use the tableNames argument to override the default table names.

const instance = makeServer({
  /* ... */
  tableNames: {
    connections: 'my_connections',
    subscriptions: 'my_subscriptions',
  },
})

// or use an async function to retrieve the names

const fetchTableNames = async () => {
  // do some work to get your table names
  return {
    connections,
    subscriptions,
  }
}
const instance = makeServer({
  /* ... */
  tableNames: fetchTableNames(),
})

@tables
Connection
  id *String
  ttl TTL
Subscription
  id *String
  ttl TTL

@indexes

Subscription
  connectionId *String
  name ConnectionIndex

Subscription
  topic *String
  name TopicIndex

import { tables as arcTables } from '@architect/functions'

const fetchTableNames = async () => {
  const tables = await arcTables()

  const ensureName = (table) => {
    const actualTableName = tables.name(table)
    if (!actualTableName) {
      throw new Error(`No table found for ${table}`)
    }
    return actualTableName
  }

  return {
    connections: ensureName('Connection'),
    subscriptions: ensureName('Subscription'),
  }
}

const subscriptionServer = makeServer({
  dynamodb: tables._db,
  schema,
  tableNames: fetchTableNames(),
})

resources:
  Resources:
    # Table for tracking connections
    connectionsTable:
      Type: AWS::DynamoDB::Table
      Properties:
        TableName: ${self:provider.environment.CONNECTIONS_TABLE}
        AttributeDefinitions:
          - AttributeName: id
            AttributeType: S
        KeySchema:
          - AttributeName: id
            KeyType: HASH
        ProvisionedThroughput:
          ReadCapacityUnits: 1
          WriteCapacityUnits: 1
    # Table for tracking subscriptions
    subscriptionsTable:
      Type: AWS::DynamoDB::Table
      Properties:
        TableName: ${self:provider.environment.SUBSCRIPTIONS_TABLE}
        AttributeDefinitions:
          - AttributeName: id
            AttributeType: S
          - AttributeName: topic
            AttributeType: S
          - AttributeName: connectionId
            AttributeType: S
        KeySchema:
          - AttributeName: id
            KeyType: HASH
        GlobalSecondaryIndexes:
          - IndexName: ConnectionIndex
            KeySchema:
              - AttributeName: connectionId
                KeyType: HASH
            Projection:
              ProjectionType: ALL
            ProvisionedThroughput:
              ReadCapacityUnits: 1
              WriteCapacityUnits: 1
          - IndexName: TopicIndex
            KeySchema:
              - AttributeName: topic
                KeyType: HASH
            Projection:
              ProjectionType: ALL
            ProvisionedThroughput:
              ReadCapacityUnits: 1
              WriteCapacityUnits: 1
        ProvisionedThroughput:
          ReadCapacityUnits: 1
          WriteCapacityUnits: 1

resource "aws_dynamodb_table" "connections-table" {
  name           = "graphql_connections"
  billing_mode   = "PROVISIONED"
  read_capacity  = 1
  write_capacity = 1
  hash_key = "id"

  attribute {
    name = "id"
    type = "S"
  }
}

resource "aws_dynamodb_table" "subscriptions-table" {
  name           = "graphql_subscriptions"
  billing_mode   = "PROVISIONED"
  read_capacity  = 1
  write_capacity = 1
  hash_key = "id"

  attribute {
    name = "id"
    type = "S"
  }

  attribute {
    name = "topic"
    type = "S"
  }

  attribute {
    name = "connectionId"
    type = "S"
  }

  global_secondary_index {
    name               = "ConnectionIndex"
    hash_key           = "connectionId"
    write_capacity     = 1
    read_capacity      = 1
    projection_type    = "ALL"
  }

  global_secondary_index {
    name               = "TopicIndex"
    hash_key           = "topic"
    write_capacity     = 1
    read_capacity      = 1
    projection_type    = "ALL"
  }
}

PubSub

graphql-lambda-subscriptions uses it's own PubSub implementation.

Subscribing to Topics

Use the subscribe function to associate incoming subscriptions with a topic.

import { subscribe } from 'graphql-lambda-subscriptions'

export const resolver = {
  Subscribe: {
    mySubscription: {
      subscribe: subscribe('MY_TOPIC'),
      resolve: (event, args, context) => {/* ... */}
    }
  }
}

Use the subscribe with SubscribeOptions to allow for filtering.

Note: If a function is provided, it will be called on subscription start and must return a serializable object.

import { subscribe } from 'graphql-lambda-subscriptions'

// Subscription agnostic filter
subscribe('MY_TOPIC', {
  filter: {
    attr1: '`attr1` must have this value',
    attr2: {
      attr3: 'Nested attributes work fine',
    },
  }
})

// Subscription specific filter
subscribe('MY_TOPIC',{
  filter: (root, args, context, info) => ({
    userId: args.userId,
  }),
})

Publishing events

Use the publish() function on your graphql-lambda-subscriptions server to publish events to active subscriptions. Payloads must be of type Record<string, any> so they can be filtered and stored.

subscriptionServer.publish({
  topic: 'MY_TOPIC',
  payload: {
    message: 'Hey!',
  },
})

Events can come from many sources

// SNS Event
export const snsHandler = (event) =>
  Promise.all(
    event.Records.map((r) =>
      subscriptionServer.publish({
        topic: r.Sns.TopicArn.substring(r.Sns.TopicArn.lastIndexOf(':') + 1), // Get topic name (e.g. "MY_TOPIC")
        payload: JSON.parse(r.Sns.Message),
      })
    )
  )

// Manual Invocation
export const invocationHandler = (payload) => subscriptionServer.publish({ topic: 'MY_TOPIC', payload })

Completing Subscriptions

Use the complete on your graphql-lambda-subscriptions server to complete active subscriptions. Payloads are optional and match against filters like events do.

subscriptionServer.complete({
  topic: 'MY_TOPIC',
  // optional payload
  payload: {
    message: 'Hey!',
  },
})

Context

Context is provided on the ServerArgs object when creating a server. The values are accessible in all callback and resolver functions (eg. resolve, filter, onAfterSubscribe, onSubscribe and onComplete).

Assuming no context argument is provided when creating the server, the default value is an object with connectionInitPayload, connectionId properties and the publish() and complete() functions. These properties are merged into a provided object or passed into a provided function.

Setting static context value

An object can be provided via the context attribute when calling makeServer.

const instance = makeServer({
  /* ... */
  context: {
    myAttr: 'hello',
  },
})

The default values (above) will be appended to this object prior to execution.

Setting dynamic context value

A function (optionally async) can be provided via the context attribute when calling makeServer.

The default context value is passed as an argument.

const instance = makeServer({
  /* ... */
  context: ({ connectionInitPayload }) => ({
    myAttr: 'hello',
    user: connectionInitPayload.user,
  }),
})

Using the context

export const resolver = {
  Subscribe: {
    mySubscription: {
      subscribe: subscribe('GREETINGS', {
        filter(_, _, context) {
          console.log(context.connectionId) // the connectionId
        },
        async onAfterSubscribe(_, _, { connectionId, publish }) {
          await publish('GREETINGS', { message: `HI from ${connectionId}!` })
        }
      })
      resolve: (event, args, context) => {
        console.log(context.connectionInitPayload) // payload from connection_init
        return event.payload.message
      },
    },
  },
}

Side effects

Side effect handlers can be declared on subscription fields to handle onSubscribe (start) and onComplete (stop) events.

export const resolver = {
  Subscribe: {
    mySubscription: {
      resolve: (event, args, context) => {
        /* ... */
      },
      subscribe: subscribe('MY_TOPIC', {
        // filter?: object | ((...args: SubscribeArgs) => object)
        // onSubscribe?: (...args: SubscribeArgs) => void | Promise<void>
        // onComplete?: (...args: SubscribeArgs) => void | Promise<void>
        // onAfterSubscribe?: (...args: SubscribeArgs) => PubSubEvent | Promise<PubSubEvent> | undefined | Promise<undefined>
      }),
    },
  },
}

Events

Global events can be provided when calling makeServer to track the execution cycle of the lambda.

Called when a WebSocket connection is first established.

const instance = makeServer({
  /* ... */
  onConnect: ({ event }) => {
    /* */
  },
})

Called when a WebSocket connection is disconnected.

const instance = makeServer({
  /* ... */
  onDisconnect: ({ event }) => {
    /* */
  },
})

onConnectionInit can be used to verify the connection_init payload prior to persistence.

Note: Any sensitive data in the incoming message should be removed at this stage.

const instance = makeServer({
  /* ... */
  onConnectionInit: ({ message }) => {
    const token = message.payload.token

    if (!myValidation(token)) {
      throw Error('Token validation failed')
    }

    // Prevent sensitive data from being written to DB
    return {
      ...message.payload,
      token: undefined,
    }
  },
})

By default, the (optionally parsed) payload will be accessible via context.

Subscribe (onSubscribe)

Called when any subscription message is received.

const instance = makeServer({
  /* ... */
  onSubscribe: ({ event, message }) => {
    /* */
  },
})

Called when any complete message is received.

const instance = makeServer({
  /* ... */
  onComplete: ({ event, message }) => {
    /* */
  },
})

Called when any error is encountered

const instance = makeServer({
  /* ... */
  onError: (error, context) => {
    /* */
  },
})

Caveats

Ping/Pong

For whatever reason, AWS API Gateway does not support WebSocket protocol level ping/pong. So you can use Step Functions to do this. See pingPong.

Socket idleness

API Gateway considers an idle connection to be one where no messages have been sent on the socket for a fixed duration (currently 10 minutes). The WebSocket spec has support for detecting idle connections (ping/pong) but API Gateway doesn't use it. This means, in the case where both parties are connected, and no message is sent on the socket for the defined duration (direction agnostic), API Gateway will close the socket. A fix for this is to set up immediate reconnection on the client side.

Socket Close Reasons

API Gateway doesn't support custom reasons or codes for WebSockets being closed. So the codes and reason strings wont match graphql-ws.