Hi dockers,
I’m relatively new to docker, having done one or two small projects here and there, and I’m now moving on to something a bit bigger, namely a webapplication divided in microservices.
Using docker-compose, I have the following containers :
- 1 for my database, called db
- 1 for the core application using django, called django (not much originality here)
- 1 for nginx, currently useless
- 1 for my central server (called central), which the user connects to through django, and redirects data through my other services using WebSockets, running on port 7777
- 2 other services (for now)
All containers belonging to a network called app-network.
Here’s the issue now. Django has no issues connecting to the db using “db” as a hostname, so it means it can resolves that, right ? However, when attempting to connect to my server using
socket = new WebSocket('ws://central:7777/ws/');
Firefox cannot open the connection to the server (Firefox can’t establish a connection to the server at ws://central:7777/ws/.). Of course, one might think the problem lies either within the Django code or the Python server, but, if I get the actual IP address of the container with docker inspect (let’s say it’s 12.13.14.15), the user can actually connect to the server and the app functions as intended. This IP changes every launch of docker, so it obviously can’t be an actual solution to use, and I’m at my wits ends about this. I’ve tried quite a bunch of solutons I found on forums :
- Disable UFW : No change
- Prune and restart my docker-compose : No change
- Change the container names, using the container_name field : No change
- Using the links field : No change
Of course, I have verified using docker network inspect :
[
{
"Name": "transcendence_app-network",
"Id": "ddc4364f674ab134e28df76173c7e2ca75fd9e57a147ca936565aacd9d9ee9d9",
"Created": "2025-01-20T10:51:05.130595115+01:00",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"383f5398662314d64cd7f2b1a9ecff77121a0498e6f8a830445015ed5a9bc52c": {
"Name": "1v1_classic",
"EndpointID": "d0fb93faee2066c7f5731c44efd8e81939d2af161449b63b1c46cbb7336511bd",
"MacAddress": "02:42:ac:12:00:05",
"IPv4Address": "172.18.0.5/16",
"IPv6Address": ""
},
"4823c901b4ada565f77890bf89c3e880ac5e362fd22c1f4ad7e8c004815a725c": {
"Name": "nginx",
"EndpointID": "29282c8bd1272c494b32aa130a56a354d4203b1465d97975e4d60cc569058c3f",
"MacAddress": "02:42:ac:12:00:07",
"IPv4Address": "172.18.0.7/16",
"IPv6Address": ""
},
"ab295a222d4e9773475b00b9f0a095dd3208f2e3fa0db6f84880d05dd451b30a": {
"Name": "central",
"EndpointID": "c36cdb0c6e6911c8c33e92b63e79e01e8f7c1d87c0edf8f466094cb712fabe5e",
"MacAddress": "02:42:ac:12:00:03",
"IPv4Address": "172.18.0.3/16",
"IPv6Address": ""
},
"e57f51628c924b767616c014bb20e6700d3e908e9c94221cfc4b7df5051c755b": {
"Name": "django",
"EndpointID": "752dc2b6b2a66cb4a4aea5c67d97219647f1b69aeb81b8070e5294038e7827e0",
"MacAddress": "02:42:ac:12:00:04",
"IPv4Address": "172.18.0.4/16",
"IPv6Address": ""
},
"f08afc38b058455813a13e79cb22708f2d9c9821e2ce7ac6b789759ab378aab7": {
"Name": "chat",
"EndpointID": "7eb94b693c6c9bc86ca4315f9286f3cea3c446da9de0057c09745ba986838edb",
"MacAddress": "02:42:ac:12:00:06",
"IPv4Address": "172.18.0.6/16",
"IPv6Address": ""
},
"f333058d5c8e74b8733ba00b89d270846d30feb013fe290d9fad3fcda094ae98": {
"Name": "db",
"EndpointID": "170d76f92eaea7da1312ae8cfd7984988b4d8c785c9cc511cb445c2eeede639c",
"MacAddress": "02:42:ac:12:00:02",
"IPv4Address": "172.18.0.2/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {
"com.docker.compose.config-hash": "c18ef3d7cc2a42c68a4e12bebbf66e96eea5f33c564b38517c31c5be6b72e090",
"com.docker.compose.network": "app-network",
"com.docker.compose.project": "transcendence",
"com.docker.compose.version": "2.32.3"
}
}
]
Connecting to my django container using docker exec -it django bash, and looking at /etc/hosts :
:/app# cat /etc/hosts
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.18.0.4 e57f51628c92
No ‘central’ there.
Of course, here’s my docker-compose :
version: '3'
services:
db:
image: postgres:17
container_name: db
environment:
POSTGRES_DB: ${DATABASE_NAME}
POSTGRES_USER: ${DATABASE_USERNAME}
POSTGRES_PASSWORD: ${DATABASE_PASSWORD}
ports:
- "5432:5432"
volumes:
- postgres_data:/var/lib/postgresql/data
env_file:
- .env
networks:
- app-network
django:
build: ./djang/
container_name: django
ports:
- "8000:8000"
depends_on:
- db
environment:
DJANGO_SECRET_KEY: ${DJANGO_SECRET_KEY}
DEBUG: ${DEBUG}
DJANGO_LOGLEVEL: ${DJANGO_LOGLEVEL}
DJANGO_ALLOWED_HOSTS: ${DJANGO_ALLOWED_HOSTS}
DATABASE_ENGINE: ${DATABASE_ENGINE}
DATABASE_NAME: ${DATABASE_NAME}
DATABASE_USERNAME: ${DATABASE_USERNAME}
DATABASE_PASSWORD: ${DATABASE_PASSWORD}
DATABASE_HOST: ${DATABASE_HOST}
DATABASE_PORT: ${DATABASE_PORT}
env_file:
- .env
networks:
- app-network
nginx:
build: ./nginx/
image: nginx
container_name: nginx
ports:
- '443:443'
restart: always
depends_on:
- django
networks:
- app-network
central:
build: ./central/
container_name: central
restart: always
ports:
- "7777:7777"
networks:
- app-network
chat:
build: ./chat/
container_name: chat
restart: always
depends_on:
- central
ports:
- "7878:7878"
networks:
- app-network
1v1_classic:
container_name: 1v1_classic
build: ./back_1v1/
restart: always
depends_on:
- central
ports:
- "8001:8001"
networks:
- app-network
volumes:
postgres_data:
networks:
app-network:
driver: bridge
(worth nothing that the main server and the microservices do manage to communicate with each others, using the ip 172.17.0.1 : await connect("ws://172.17.0.1:8001/", ping_interval=10, ping_timeout=None))
I might be repeating myself, but the project fully works using “hard coded” IPs, so I think we can safely exclude the problem coming from my code. Did I miss something extremely obvious ? This is tearing me apart
Thanks in advance for your time and help.
