CODEWITHSUNDEEP
dockergoogle-cloud-run
Steren
Steren

Reputation: 7909

Container port forwarding

I have a binary that listens on port 3000, however, Google Cloud Run wants me to listen on the port defined by $PORT, that defaults to 8080.

Is there a way to make my container bind to 8080 and then forward the incoming requests to 3000? for examplem by adding a short script and one line to my Dockerfile, it would make my container listen on 8080 and forward to my binary.

Upvotes: 3

Views: 1679

Answers (2)

codestation
codestation

Reputation: 3498

If you can install a run a second process and start it along your main process then install and run socat using the following command:

socat tcp-listen:8080,fork,reuseaddr tcp-connect:localhost:3000

This way socat will bind to the 8080 port and send all the traffic to the port 3000 where your binary is listening.

Outside of Cloud Run: If you cannot touch your image nor your container then you can still run socat on an additional container, for example:

version: '3.5'
services:
  proxy:
    image: alpine/socat:1.0.3
    command: tcp-listen:8080,fork,reuseaddr tcp-connect:myservice:3000
    networks:
      - mynet
networks:
  mynet:
    external: true

Where mynet is the network where your binary is running and myservice is the service name of your binary.

Upvotes: 1

sethvargo
sethvargo

Reputation: 26997

The code below is untested, but the general idea is this:

  1. Use a shell-based startup script
  2. Enable iptables
  3. Route traffic from srcPort to dstPort
  4. Exec the original binary

In the Dockerfile, replace the ENTRYPOINT with a startup script:

FROM debian:9 # or another container that has iptables available
RUN apt-get install iptables
EXPOSE 8080
ENTRYPOINT /bin/startup.sh /bin/original

And then write a startup script that enables iptables and forwards inbound traffic on 8080 to 3000 inside the container:

#!/usr/bin/env bash
set -e

sed -i 's/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1/g' /etc/sysctl.conf
sysctl -p
systemctl start iptables

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 8080 -j REDIRECT --to-port 3000
iptables -t nat -A PREROUTING -i eth0 -p udp --dport 8080 -j REDIRECT --to-port 3000


unshift 
exec "$@"

Upvotes: 2

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