api-gateway-designer

name	api-gateway-designer
version	2.0
trigger	API gateway, microservice communication, API design, route patterns
description	Design and implement scalable API gateways, RESTful APIs, GraphQL endpoints, WebSocket handlers, and microservice communication patterns. Use when creating API routes, designing endpoints, implementing middleware, or setting up service mesh architectures.

API Gateway Designer

REST API Patterns

Resource-Oriented Endpoints

router.get('/api/users', requireAuth, async (req, res) => {
  const users = await userService.list(req.query);
  res.json({ data: users, meta: { total: users.length } });
});

router.post('/api/users', requireAuth, async (req, res) => {
  const user = await userService.create(req.body);
  res.status(201).json({ data: user });
});

router.get('/api/users/:id', requireAuth, async (req, res) => {
  const user = await userService.getById(req.params.id);
  if (!user) throw new NotFoundError('User not found');
  res.json({ data: user });
});

Query Builder with Pagination

class QueryBuilder<T> {
  build() {
    let q = db.select().from(this.table);
    if (this.query.filter) {
      q = q.where(and(...conditions));
    }
    q = q.limit(this.query.limit).offset((this.query.page - 1) * this.query.limit);
    return q;
  }
}

GraphQL Schema

builder.prismaObject('User', {
  fields: (t) => ({
    id: t.exposeID('id'),
    email: t.exposeString('email'),
    posts: t.relation('posts'),
  })
});

builder.queryType({
  fields: (t) => ({
    user: t.prismaField({
      type: 'User',
      args: { id: t.arg.id({ required: true }) },
      resolve: (query, _, args) => db.user.findUnique({ ...query, where: { id: args.id } })
    })
  })
});

WebSocket Handler

export class WebSocketManager {
  broadcast(channel: string, payload: unknown) {
    this.clients.forEach(client => {
      if (client.subscriptions.has(channel)) {
        client.send(JSON.stringify({ channel, payload }));
      }
    });
  }
}

Middleware

export const rateLimitMiddleware = async (req, res, next) => {
  try {
    await rateLimiter.consume(req.user?.id || req.ip);
    next();
  } catch {
    res.status(429).json({ error: 'Too many requests' });
  }
};

Protocol

1. Assess — Understand the specific requirement and context
2. Plan — Determine the approach based on the guidance above
3. Execute — Apply the api gateway designer methodology
4. Verify — Validate the output against expected standards
5. Report — Document results and any issues encountered