502 Bad Gateway

The server acting as a middleman (proxy) received an invalid response from the upstream server it was trying to reach.

When and Why to Use It

Use this proxying requests. If your Nginx server tries to talk to your Node.js app, but the Node app returns an invalid HTTP response, Nginx will return a 502 to the user.

Usage Examples

Shokupan (Functional)

import { HttpException, get } from 'shokupan';

export const proxyWeather = get('/weather', async () => {
    const response = await fetch('http://upstream-weather-api.internal');

    if (!response.ok) {
        throw new HttpException('Upstream returned invalid response', 502);
    }

    return response.json();
});

Shokupan (Controller)

import { Controller, Get, HttpException } from 'shokupan';

@Controller('/api')
export class ProxyController {
    @Get('/weather')
    async proxyWeather() {
        const response = await fetch('http://upstream-weather-api.internal');

        if (!response.ok) {
            throw new HttpException('Upstream returned invalid response', 502);
        }

        return response.json();
    }
}

Express

import express from 'express';
const app = express();

app.get('/weather', async (req, res) => {
    try {
        const response = await fetch('http://upstream-weather-api.internal');
        if (!response.ok) throw new Error('Bad upstream');
        res.json(await response.json());
    } catch (err) {
        res.status(502).json({ error: 'Bad Gateway - Upstream failed' });
    }
});

Nest

import { Controller, Get, BadGatewayException } from '@nestjs/common';

@Controller('weather')
export class ProxyController {
  @Get()
  async proxyWeather() {
    try {
      const response = await fetch('http://upstream-weather-api.internal');
      if (!response.ok) throw new Error('Bad upstream');
      return await response.json();
    } catch (err) {
      throw new BadGatewayException('Upstream returned invalid response');
    }
  }
}

Koa

import Koa from 'koa';
const app = new Koa();

app.use(async ctx => {
  if (ctx.path === '/weather' && ctx.method === 'GET') {
    try {
      const response = await fetch('http://upstream-weather-api.internal');
      if (!response.ok) throw new Error('Bad upstream');
      ctx.body = await response.json();
    } catch (err) {
      ctx.status = 502;
      ctx.body = { error: 'Bad Gateway - Upstream failed' };
    }
  }
});