how to correctly configure ngrok docker container for node or react app? - node.js

Question

I'm trying to use ngrok for exposing my localhost to share my node backend with a friend.
The problem I face is that whenever I start node backend the ngrok container couldn't work cause it trys to map the same port as being used by node.
node:events:371
throw er; // Unhandled 'error' event
^
Error: listen EADDRINUSE: address already in use :::5000
at Server.setupListenHandle [as _listen2] (node:net:1319:16)
at listenInCluster (node:net:1367:12)
at Server.listen (node:net:1454:7)
at Function.listen (C:\Users\928941\node_backends\express-for-react\node_modules\express\lib\application.js:618:24)
at Object.<anonymous> (C:\Users\928941\node_backends\express-for-react\app.js:27:5)
at Module._compile (node:internal/modules/cjs/loader:1101:14)
at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
at Module.load (node:internal/modules/cjs/loader:981:32)
at Function.Module._load (node:internal/modules/cjs/loader:822:12)
at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:79:12)
Emitted 'error' event on Server instance at:
at emitErrorNT (node:net:1346:8)
code: 'EADDRINUSE',
errno: -4091,
syscall: 'listen',
address: '::',
port: 5000
}
[nodemon] app crashed - waiting for file changes before starting...
the above error simply means that port 5000 is currently in use(i.e., by ngrok docker container).
If I run the node app first and try to run the docker container after that I get this error from docker.
[+] Running 1/0
- Container docker-compose_for_ngrok_ngrok_1 Created 0.0s
Attaching to ngrok_1
Error response from daemon: Ports are not available: listen tcp 0.0.0.0:5000: bind: Only one usage of each socket address (protocol/network address/port) is normally permitted.
This is my docker-compose.yml file
version: '3'
services:
ngrok:
image: ngrok/ngrok:alpine
ports:
- 4040:4040
- 5000:5000
environment:
- NGROK_AUTHTOKEN=my_authentication_token
command: http 5000
the compose file is same as this docker run command so anyone can be used.
docker run -d -p 4040:4040 -p 5000:5000 -e NGROK_AUTHTOKEN=my_token ngrok/ngrok:alpine http 5000
Port 4040 is default ngrok port for dashboard and it works fine for me.
I'm also facing this issue with react app as well.

Answer 1

I'm not sure if you are running on linux, but you might not need to do any port forwarding if you use the --net=host option. See the examples in https://hub.docker.com/r/ngrok/ngrok/
The equivalent for a docker compose file is network_mode:https://docs.docker.com/compose/compose-file/compose-file-v3/#network_mode
So your docker compose would be:
version: '3'
services:
ngrok:
image: ngrok/ngrok:alpine
environment:
- NGROK_AUTHTOKEN=my_authentication_token
command: http 5000
network_mode: "host"
Assuming your node is running on localhost:5000, if you start a docker container and use the same network, then you don't need to open any ports.
If you are using mac or windows, you will need to use the workaround here:
https://docs.docker.com/desktop/mac/networking/#use-cases-and-workarounds
Which is to use command: http host.docker.internal:5000 instead.