Application reachable from outside, but not from inside the container

Hello,

I have problem with my application container unable to reach another container behind the nginx reverse proxy.

I have 2 applications running each on different subdomain (and different containers):

app1: app1.domain.com app2: app2.domain.com

I can reach both of them from outside world, it works perfectly. But when I try to reach app2 from app1, it times out. Ping works just fine, DNS records seem to be OK. But wget http://app2.domain.com or wget https://app2.domain.com fails. I think it doesn’t reach the nginx proxy correctly for some reason.

Host machine can access both app1.domain.com and app2.domain.com without any problems. There must be something with docker networking.

I’m running Ubuntu 18.04.4 LTS with Docker 19.03.12, build 48a66213fe

version: "3.1"
services:
  # Nginx proxy - the webserver user will directly face
  # Reverse proxy for all apps, redirects HTTP requests to app
  nginx-proxy:
    image: nginx:1.15-alpine
    container_name: nginx-proxy
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - conf:/etc/nginx/conf.d
      - vhost:/etc/nginx/vhost.d
      - html:/usr/share/nginx/html
      - certs:/etc/nginx/certs:ro
    labels:
      - "com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy"
    restart: always

  # Generator for nginx configuration
  docker-gen:
    image: jwilder/docker-gen
    command: -notify-sighup nginx-proxy -watch /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf
    container_name: nginx-proxy-gen
    depends_on:
      - nginx-proxy
    volumes:
      - conf:/etc/nginx/conf.d
      - vhost:/etc/nginx/vhost.d
      - certs:/etc/nginx/certs:ro
      - ./docker/nginx/nginx.tmpl:/etc/docker-gen/templates/nginx.tmpl:ro
      - /var/run/docker.sock:/tmp/docker.sock:ro
    labels:
      - "com.github.jrcs.letsencrypt_nginx_proxy_companion.docker_gen"
    restart: always

  # Container to generate SSL certificates
  letsencrypt:
    image: jrcs/letsencrypt-nginx-proxy-companion
    container_name: nginx-proxy-le
    depends_on:
      - nginx-proxy
      - docker-gen
    volumes:
      - vhost:/etc/nginx/vhost.d
      - html:/usr/share/nginx/html
      - certs:/etc/nginx/certs
      - /var/run/docker.sock:/var/run/docker.sock:ro
    restart: always

  # Actual app
  app:
    image: registry.gitlab.com/klinki/docker-registry/app:latest
    expose:
      - "80"
    environment:
      VIRTUAL_HOST: app1.domain.com
      LETSENCRYPT_HOST: app1.domain.com
      LETSENCRYPT_EMAIL: [e-mail]

  app_pse:
    image: registry.gitlab.com/klinki/docker-registry/app2:latest
    environment:
      VIRTUAL_HOST: app2.domain.com
      LETSENCRYPT_HOST: app2.domain.com
      LETSENCRYPT_EMAIL: [e-mail]

volumes:
  conf:
  vhost:
    driver: local
    driver_opts:
      type: "none"
      o: "bind"
      device: "/root/inviser/docker/nginx/vhost.d"
  html:
  certs:
  dbvolume:

[klinki]

@tkw1536 Firewall was good idea! I’m confused why it worked from the outside, but I was missing ports 80 and 443 in ufw. I added rule to allow all traffic on these ports and now it works.

[ugened47]

@klinki Having similar issue using nginx-proxy https://github.com/nginx-proxy/nginx-proxy/issues/1469#issuecomment-657248086