Outbound WebSocket connection from Docker container does not work

user_15798731 0
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I have a simple TypeScript program running on Docker, and this program would like to open a Websocket connection to an outside Websocket server. Something like this

-----------------------                   ------------------------------
| My Local Docker     |                   | my.ws-server.somewhere.com |                   
|                     |                   |                            |
|    WS client        |---> Internet----->| WS server                  |
-----------------------                   ------------------------------

When I run (ts-node test.js) the code with the WS client on my dev environment outside Docker, it works fine and can connect without any issues:

let ws = new WebSocket("ws://my.ws-server.somewhere.com", [], { })
ws.onopen = () => {
  console.log('Connection opened ok! ')
}

However, when I put this some thing inside Docker and run it there, the connection is refused. The program starts the connection attempt as it should, but there is just a timeout and the connection is never opened. I guess this has something to do with Docker network? If I want to open an outbound connection from Docker to the outside world, do I need to define some routes or something?

My Docker setup

Dockerfile

FROM node:12.18.3

RUN mkdir /src

WORKDIR /src
ADD ./package.json /src/package.json
RUN npm install

EXPOSE 3000

docker-compose.yml

version: "3.4"
services:
  my-service:
      container_name: my-service
      restart: always
      build:
          context: .
          dockerfile: my-service.dockerfile
      volumes:
          - ".:/src"

(I noticed that I can make this work by adding network_mode: "host" to docker compose, but that's not what I would really want to do so that I could keep the normal inbound port mappings)

typescript docker node.js websocket
1 Answers

First, you should check if your websocket is opened on the good port, I see you expose port 3000. Also you must check if your proxy is well set up for the port. It could be also possible that you need a secure websocket connection to make it work (then the url becomes wss://mywebsocket.something.com).

Give me Feedback when you can

user_52849530
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