A reverse proxy plug for proxying a request to another URL using HTTPoison. Perfect when you need to transparently proxy requests to another service but also need to have full programmatic control over the outgoing requests.

This project grew out of a fork of elixir-reverse-proxy. Advantages over the original include more flexible upstreams, zero-delay chunked transfer encoding support, HTTP2 support with Cowboy 2 and focus on being a composable Plug instead of providing a standalone reverse proxy application.

Add reverse_proxy_plug to your list of dependencies in mix.exs:

def deps do
  [
    {:reverse_proxy_plug, "~> 1.2.1"}
  ]
end

The plug works best when used with Plug.Router.forward/2. Drop this line into your Plug router:

forward("/foo", to: ReverseProxyPlug, upstream: "//example.com/bar")

Now all requests matching /foo will be proxied to the upstream. For example, a request to /foo/baz made over HTTP will result in a request to http://example.com/bar/baz.

You can also specify the scheme or choose a port:

forward("/foo", to: ReverseProxyPlug, upstream: "https://example.com:4200/bar")

In general, the :upstream option should be a well formed URI parseable by URI.parse/1.

The Phoenix default autogenerated project assumes that you'll want to parse all request bodies coming to your Phoenix server and puts Plug.Parsers directly in your endpoint.ex. If you're using something like ReverseProxyPlug, this is likely not what you want — in this case you'll want to move Plug.Parsers out of your endpoint and into specific router pipelines or routes themselves.

You can modify various aspects of the client request by simply modifying the Conn struct. In case you want to modify the request body, fetch it using Conn.read_body/2, make your changes, and leave it under Conn.assigns[:raw_body]. ReverseProxyPlug will use that as the request body. In case a custom raw body is not present, ReverseProxyPlug will fetch it from the Conn struct directly.

ReverseProxyPlug supports two response modes:

• :stream (default) - The response from the plug will always be chunk encoded. If the upstream server sends a chunked response, ReverseProxyPlug will pass chunks to the clients as soon as they arrive, resulting in zero delay.

• :buffer - The plug will wait until the whole response is received from the upstream server, at which point it will send it to the client using Conn.send_resp. This allows for processing the response before sending it back using Conn.register_before_send.

You can choose the response mode by passing a :response_mode option:

forward("/foo", to: ReverseProxyPlug, response_mode: :buffer, upstream: "//example.com/bar")

ReverseProxyPlug will automatically respond with 502 Bad Gateway in case of network error. To inspect the HTTPoison error that caused the response, you can pass an :error_callback option.

plug(ReverseProxyPlug,
  upstream: "example.com",
  error_callback: fn error -> Logger.error("Network error: #{inspect(error)}") end
)

ReverseProxyPlug is released under the MIT License.