Proxy your HTTP requests to another server, with hooks. This fastify plugin forwards all requests received with a given prefix (or none) to an upstream. All Fastify hooks are still applied.

@fastify/http-proxy is built on top of @fastify/reply-from, which enables single route proxying.

This plugin can be used in a variety of circumstances, for example, if you have to proxy an internal domain to an external domain (useful to avoid CORS problems) or to implement your own API gateway for a microservices architecture.

Fastify 5.x. See @fastify/http-proxy v9.x for Fastify 4.x compatibility.

npm i @fastify/http-proxy fastify

const Fastify = require('fastify');
const server = Fastify();

server.register(require('@fastify/http-proxy'), {
  upstream: 'http://my-api.example.com',
  prefix: '/api', // optional
  http2: false, // optional
});

server.listen({ port: 3000 });

This will proxy any request starting with /api to http://my-api.example.com. For instance, http://localhost:3000/api/users will be proxied to http://my-api.example.com/users.

If you want to have different proxies on different prefixes you can register multiple instances of the plugin as shown in the following snippet:

const Fastify = require('fastify');
const server = Fastify();
const proxy = require('@fastify/http-proxy');

// /api/x will be proxied to http://my-api.example.com/x
server.register(proxy, {
  upstream: 'http://my-api.example.com',
  prefix: '/api', // optional
  http2: false, // optional
});

// /rest-api/123/endpoint will be proxied to http://my-rest-api.example.com/123/endpoint
server.register(proxy, {
  upstream: 'http://my-rest-api.example.com',
  prefix: '/rest-api/:id/endpoint', // optional
  rewritePrefix: '/:id/endpoint', // optional
  http2: false, // optional
});

// /auth/user will be proxied to http://single-signon.example.com/signon/user
server.register(proxy, {
  upstream: 'http://single-signon.example.com',
  prefix: '/auth', // optional
  rewritePrefix: '/signon', // optional
  http2: false, // optional
});

// /user will be proxied to http://single-signon.example.com/signon/user
server.register(proxy, {
  upstream: 'http://single-signon.example.com',
  rewritePrefix: '/signon', // optional
  http2: false, // optional
});

server.listen({ port: 3000 });

Notice that in this case, it is important to use the prefix option to tell the proxy how to properly route the requests across different upstreams.

Also, notice paths in upstream are ignored, so you need to use rewritePrefix to specify the target base path.

For other examples, see example.js.

@fastify/http-proxy can track and pipe the request-id across the upstreams. Using the hyperid module and the @fastify/reply-from built-in options a fairly simple example would look like this:

const Fastify = require('fastify');
const proxy = require('@fastify/http-proxy');
const hyperid = require('hyperid');

const server = Fastify();
const uuid = hyperid();

server.register(proxy, {
  upstream: 'http://localhost:4001',
  replyOptions: {
    rewriteRequestHeaders: (originalReq, headers) => ({
      ...headers,
      'request-id': uuid(),
    }),
  },
});

server.listen({ port: 3000 });

This fastify plugin supports all the options of @fastify/reply-from plus the following.

Note that this plugin is fully encapsulated, and non-JSON payloads will be streamed directly to the destination.

An URL (including protocol) that represents the target server to use for proxying.

The prefix to mount this plugin on. All the requests to the current server starting with the given prefix will be proxied to the provided upstream.

Parametric path is supported. To register a parametric path, use the colon before the parameter name.

The prefix will be removed from the URL when forwarding the HTTP request.

Rewrite the prefix to the specified string. Default: ''.

Destination paths containing dot-segments that could escape the rewritten prefix are rejected with a 400 response. This check also accounts for percent-encoded / and \ path separators.

A preHandler to be applied on all routes. Useful for performing actions before the proxy is executed (e.g. check for authentication).

A function to replace the default HTTP proxy handler. It receives the request, reply, rewritten destination, and reply options.

By default, the handler calls reply.from(dest, options). Use this option to customize the response handling while keeping the proxy URL rewriting behavior.

fastify.register(proxy, {
  upstream: 'http://api-upstream.com',
  async handler (request, reply, dest, options) {
    return reply.from(dest, options)
  }
})

When this option is false, you will be able to access the body but it will also disable direct pass through of the payload. As a result, it is left up to the implementation to properly parse and proxy the payload correctly.

For example, if you are expecting a payload of type application/xml, then you would have to add a parser for it like so:

fastify.addContentTypeParser('application/xml', (req, done) => {
  const parsedBody = parsingCode(req);
  done(null, parsedBody);
});

Specify preValidation function to perform the validation of the request before the proxy is executed (e.g. check request payload).

fastify.register(proxy, {
  upstream: `http://your-target-upstream.com`,
  preValidation: async (request, reply) => {
    if (request.body.method === 'invalid_method') {
      return reply.code(400).send({ message: 'payload contains invalid method' });
    }
  },
});

An object accessible within the preHandler via reply.context.config. See Config in the Fastify documentation for information on this option. Note: this is merged with other configuration passed to the route.

Object with reply options for @fastify/reply-from.

By default, @fastify/http-proxy will rewrite the location header when a request redirects to a relative path. In other words, the prefix will be added to the relative path.

If you want to preserve the original path, this option will disable this internal operation. Default: true.

Note that the rewriteHeaders option of @fastify/reply-from will retrieve headers modified (reminder: only location is updated among all headers) in parameter but with this option, the headers are unchanged.

An array that contains the types of the methods. Default: ['DELETE', 'GET', 'HEAD', 'PATCH', 'POST', 'PUT', 'OPTIONS'].

An array that contains the routes to handle. Default: ['/', '/*'].

A function that will be executed before rewriting the URL. It receives the URL, the request parameters and the prefix and must return the new URL.

The function cannot return a promise.

// `/api/abc` will be proxied to `http://api-upstream.com/api2/xyz`
fastify.register(proxy, {
  upstream: `http://api-upstream.com`,
  prefix: '/api',
  rewritePrefix: '/api2/',
  preRewrite (url, params, prefix) {
    return url.replace('abc', 'xyz');
  }
})

This module has partial support for forwarding websockets by passing a websocket boolean option.

A few things are missing:

1. request id logging
2. support ignoreTrailingSlash
3. forwarding more than one subprotocols. Note: Only the first subprotocol is being forwarded

Pull requests are welcome to finish this feature.

The proxy can coexist with other upgrade listeners on the same server, such as @fastify/websocket, regardless of the registration order: when other listeners are present the proxy only handles upgrades targeting one of its prefixes and leaves the rest untouched. A proxy mounted at the root (no prefix) owns every upgrade.

Working only if property websocket is true.

An URL (including protocol) that represents the target websockets to use for proxying websockets. Accepted both https:// and wss://.

Note that if property wsUpstream not specified then proxy will try to connect with the upstream property.

The options passed to new ws.Server().

The options passed to the WebSocket constructor for outgoing websockets.

It also supports an additional rewriteRequestHeaders(headers, request) function that can be used to write the headers before opening the WebSocket connection. This function should return an object with the given headers. The default implementation forwards the cookie header.

Experimental. (default: disabled)

Reconnection feature detects and closes broken connections and reconnects automatically, see how to detect and close broken connections. The connection is considered broken if the target does not respond to the ping messages or no data is received from the target.

The wsReconnect option contains the configuration for the WebSocket reconnection feature. To enable the feature, set the wsReconnect option to an object with the following properties:

• pingInterval: The interval between ping messages in ms (default: 30_000).
• maxReconnectionRetries: The maximum number of reconnection retries (1 to Infinity, default: Infinity).
• reconnectInterval: The interval between reconnection attempts in ms (default: 1_000).
• reconnectDecay: The decay factor for the reconnection interval (default: 1.5).
• connectionTimeout: The timeout for establishing the connection in ms (default: 5_000).
• reconnectOnClose: Whether to reconnect on close, as long as the connection from the related client to the proxy is active (default: false).
• logs: Whether to log the reconnection process (default: false).

See the example in examples/reconnection.

On websocket events, the following hooks are available, note the hooks are all synchronous. The context object is passed to all hooks and contains the log property.

• onIncomingMessage: A hook function that is called when the request is received from the client onIncomingMessage(context, source, target, { data, binary }) (default: undefined).
• onOutgoingMessage: A hook function that is called when the response is received from the target onOutgoingMessage(context, source, target, { data, binary }) (default: undefined).
• onConnect: A hook function that is called when the connection is established onConnect(context, source, target) (default: undefined).
• onDisconnect: A hook function that is called when the connection is closed onDisconnect(context, source) (default: undefined).
• onReconnect: A hook function that is called when the connection is reconnected onReconnect(context, source, target) (default: undefined). The function is called if reconnection feature is enabled.
• onPong: A hook function that is called when the target responds to the ping onPong(context, source, target) (default: undefined). The function is called if reconnection feature is enabled.

It can be used to get the final URL and options that @fastify/http-proxy would have used to invoke reply.from.

A typical use is to override the request URL:

preHandler (request, reply, done) {
  if (request.url !== '/original') {
    done()
    return
  }

  const { url, options } = reply.fromParameters('/updated', { ...request.params, serverId: 42 })
  reply.from(url, options)
}

The following benchmarks were generated on a dedicated server with an Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz and 64GB of RAM:

The results were gathered on the second run of autocannon -c 100 -d 5 URL.

• Perform validations for incoming data
• Finish implementing websocket

Licensed under MIT.