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@cocrafts/graphql-lambda

GraphQL Lambda adapters for AWS Lambda functions with support for HTTP and WebSocket APIs, Redis storage, and distributed pub/sub.

Installation

npm install @cocrafts/graphql-lambda

Features

  • Unified GraphQL Interface: Single schema works across HTTP, WebSocket, and Lambda environments
  • AWS Lambda Support: Native adapters for API Gateway HTTP and WebSocket APIs
  • Redis Integration: Distributed storage and pub/sub for serverless environments
  • Cross-Environment: Same GraphQL schema runs locally and on AWS Lambda

Serverless Considerations

Context Serialization Requirements

Context must be JSON serializable: All context data is persisted to Redis between Lambda invocations using flattened dot-notation (e.g., extra.user.id). Functions, classes, and circular references are not supported.

// Supported: Plain JSON data
ctx.extra.user = { id: '123', name: 'John', roles: ['admin'] };

// Not supported: Functions, circular references
ctx.extra.callback = () => console.log('hello');
ctx.extra.user.parent = ctx.extra.user;

Subscription Execution Model

No async iterators: Unlike server implementations, serverless uses a custom pubsub engine. Each subscription resolver runs once during setup, not for each published event. Published events are sent directly to clients without re-running GraphQL execution or validation.

// Server: Re-executes GraphQL for each event
for await (const event of asyncIterator) {
	yield await execute({ schema, document, rootValue: event });
}

// Serverless: Direct event forwarding
await pubsub.publish('topic', payload); // No re-execution

Key Limitations

  • No field-level filtering: Server implementations can filter/transform fields per event; serverless sends raw published payloads
  • No real-time validation: Schema changes don't affect in-flight subscriptions until reconnection
  • No per-event context: Published events don't have access to subscription-time context or variables
  • Context reconstruction: Context is rebuilt from Redis on each Lambda invocation

Best Practices

Context Management

onConnect: async ctx => {
	ctx.extra = {
		userId: await authenticateUser(ctx.connectionParams?.token),
		subscriptionCount: 0,
	};
	return true;
};

Subscription Design

// Design for direct payload forwarding
subscribe: () => pubsub.subscribe('CHAT_MESSAGE');

// Publish complete, typed payloads
await pubsub.publish('CHAT_MESSAGE', {
	messageAdded: {
		id: '123',
		text: 'Hello',
		timestamp: new Date().toISOString(),
	},
});

When to Use

Good for: Event-driven applications, infrequent real-time updates, variable traffic patterns, cost optimization.

Consider alternatives for: High-frequency updates, complex field filtering, low-latency requirements, heavy context usage.

Usage

Local Development

import { createHandler } from 'graphql-http/lib/use/http';
import { useServer } from 'graphql-ws/use/ws';
import { DefaultGraphQLPubSub } from '@cocrafts/graphql-pubsub';

const graphqlHandler = createHandler(graphqlHttpOptions);
useServer(graphqlWsOptions, wss);

AWS Lambda WebSocket

import { AWSGraphQLWsAdapter } from '@cocrafts/graphql-lambda';

const mergedOptions = {
	...graphqlWsOptions,
	storage,
	gateway,
	pubsub,
};

export const handler = AWSGraphQLWsAdapter(mergedOptions);

Shared Infrastructure

import { ApiGatewayManagementApiClient } from '@aws-sdk/client-apigatewaymanagementapi';
import { createClient } from 'redis';

export const redis = createClient({ url: 'redis://localhost:6379' });
export const gateway = new ApiGatewayManagementApiClient({
	region: 'us-east-1',
});

export const storage = {
	set: async (key: string, value: string) => await redis.set(key, value),
	get: async (key: string) => await redis.get(key),
};

Build

bun run build

Generates ESM, CommonJS, and TypeScript declaration files in the dist/ directory.