how to access local port with an active ufw from within a container

README.md

how to access local port with an active ufw from within a container

main solution

TLDR: specify network subnet in compose file, then allow in ufw.

• in docker-compose setup network with specified subnet.
• in docker-compose add below to access localhost via host.docker.internal.

myservice:
    extra_hosts:
        - "host.docker.internal:host-gateway"

• allow subnet in ufw sudo ufw allow from 172.18.0.1/16
• in container, call directly docker exec test-curl-1 curl host.docker.internal:8112
• ??? setup socat, don't really think this is necessary unless you are routing sockets. docker exec test-curl-1 curl proxy:8112

alternatively, use network_mode: host

-- ref

https://gist.github.com/lalyos/09c0e6131b9de8240eb7
https://github.com/docker/compose/issues/4336
https://stackoverflow.com/questions/24319662/from-inside-of-a-docker-container-how-do-i-connect-to-the-localhost-of-the-mach
https://forums.docker.com/t/how-to-reach-localhost-on-host-from-docker-container/113321/16
https://github.com/moby/moby/pull/42785
https://stackoverflow.com/questions/46845381/how-do-configure-docker-compose-to-use-a-given-subnet-if-a-variable-is-set-or-c
https://docs.docker.com/compose/networking/
https://superuser.com/questions/1709013/enable-access-to-host-service-with-ubuntu-firewall-from-docker-container

docker-compose.yml

version: '3.7'
services:
    proxy:
        #??? image: docker-friendly
        #??? command: TCP-L:2375,fork UNIX:/var/run/docker.sock
        #volumes:
        #    - /var/run/docker.sock:/var/run/docker.sock
        image: bobrik/socat
        restart: always
        command: TCP4-LISTEN:8112,fork,reuseaddr TCP4:host.docker.internal:8112
        extra_hosts:
            - "host.docker.internal:host-gateway"
        expose:
            - 8112
        networks:
            default:
    curl:
        extra_hosts:
            - "host.docker.internal:host-gateway"
        image: curlimages/curl
        restart: always
        command: "sleep 1000"
        networks:
            default:
networks:
  default:
    driver: bridge
    ipam:
      driver: default
      config:
      - subnet: 172.18.0.0/16