debug : two docker-compose services can’t connect ?

Sometimes you create a docker-compose by your own, but when launching your stack, the two services seems to not being reachable. An example : In your docker-compose, your backend can’t connect to the database

First import your docker-compose file in the playground. Then you could see how things are connected together.

If the links look like bellow, so you have to connect the two services to a common network allow them to reach others

So this (upper) look like this (bellow)

Your docker-compose services are connected but can’t reach ?

Have you used the correct hostname ? In the docker-compose bellow, the nginx serice have to use http://backend to reach the backend service and not localhost ! Docker-compose networks have their own DNS.

name: test
services:
  nginx:
    image: nginx:latest
    networks:
      - hephaestus_chick
  backend:
    networks:
      - hephaestus_chick
networks:
  hephaestus_chick:

The hostnames are correct ?

try using the ping cmd from a container to reach the other one. You can use the docker exec to launch a ping from one container to another :

docker exec container_name_nginx ping -c 3 backend

if the container still look to be unreachable, try to inspect the network using :

docker network inspect docker_network_name

That will give you an output like this :

[
  {
    "Name": "dionysus_calf_hephaestus_chick",
    "Id": "039db46f5b3e2a6bd9c4bc322eabd849c1211c979f4faadcb1aa3ecc32d5a509",
    "Created": "2024-12-04T18:07:00.669412851-05:00",
    "Scope": "local",
    "Driver": "bridge",
    "EnableIPv6": false,
    "IPAM": {
      "Driver": "default",
      "Options": null,
      "Config": [
        {
          "Subnet": "192.168.148.0/24",
          "Gateway": "192.168.148.1"
        }
      ]
    },
    "Internal": false,
    "Attachable": false,
    "Ingress": false,
    "ConfigFrom": {
      "Network": ""
    },
    "ConfigOnly": false,
    "Containers": {
      "06fd9566ba0161b8e4a80cf7b84ae27b9d089a355949db5e96075aae31e81f6e": {
        "Name": "dionysus_calf-backend-1",
        "EndpointID": "eae118f0954db6caad3257641f24416621047b5896d8dd4f955d34ec0d9f5b32",
        "MacAddress": "02:42:c0:a8:94:02",
        "IPv4Address": "192.168.148.2/24",
        "IPv6Address": ""
      },
      "9ac2a60d0d80285bfed27da7b5e8ecf991a399b5347d99bd4f002c58c7f90c46": {
        "Name": "dionysus_calf-Nginx-1",
        "EndpointID": "8f1b762e8a8ac18e67d62b5fb7e655e48d91149e9a9bedd58657ffc705a50e9b",
        "MacAddress": "02:42:c0:a8:94:03",
        "IPv4Address": "192.168.148.3/24",
        "IPv6Address": ""
      }
    },
    "Options": {},
    "Labels": {
      "com.docker.compose.network": "hephaestus_chick",
      "com.docker.compose.project": "dionysus_calf",
      "com.docker.compose.version": "2.29.7"
    }
  }
]

Here, under Containers, you can see all connected containers to the network