Question 237567 in Docker Question posted in
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Docker Networking services unable to connect to each other

I have this docker compose file shown file

version: '3'

services:
  backend-flask:
    build: ./backend   

  frontend-fligh:
    build: ./frontend-fligh
    ports:
      - "3000:3000"
    depends_on:
      - backend-flask

In my frontend I’m trying to make a backend api call by doing

const response = await fetch('http://backend-flask:5000/search', {
                    method: 'POST',
                    headers: {
                        'Content-Type': 'application/json'
                    },
                    body: JSON.stringify(query)
                });

but this requests returns me this error
POST http://backend-flask:5000/search net::ERR_NAME_NOT_RESOLVED

in my app.py of my backend flask application the route is defined as well

app = Flask(__name__)
CORS(app) #for production change to have only my site


@app.route('/search', methods=['POST'])
//more code

also note that this works if i change it from backend-flask to localhost:5000/search

i inspected the network and the containers are all in the same network, I’m really lost here, and not sure why it’s not working

jasonwang@Jasons-MacBook-Pro startUp % docker network inspect startup_default
[
    {
        "Name": "startup_default",
        "Id": "f9507df9f26968c4665da09bf90b24904267b177476c3654197d4b9afbf1dd78",
        "Created": "2023-08-25T02:26:45.523880875Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.19.0.0/16",
                    "Gateway": "172.19.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "1278a785f11c2227638d12aba3c5286a29346134801b43481fcedc5d15037b12": {
                "Name": "startup-redis-1",
                "EndpointID": "cfaf2be033ce04fd9f7cdd5cba4d287d0d3a9ee77edd79324fe8b6dfd2a93ca6",
                "MacAddress": "02:42:ac:13:00:02",
                "IPv4Address": "172.19.0.2/16",
                "IPv6Address": ""
            },
            "5ca87c376d0342d67e07a2452f2ae188af710c65753894fdddda99bb05e0e902": {
                "Name": "startup-backend-flask-1",
                "EndpointID": "24bd57249b98e595b54846d5581655798730b3eb475624fe057599ad1f492b5c",
                "MacAddress": "02:42:ac:13:00:03",
                "IPv4Address": "172.19.0.3/16",
                "IPv6Address": ""
            },
            "6a968c8e2bad884cc56540cc43699dc51c479486693e60209add3e890e84d94c": {
                "Name": "startup-frontend-fligh-1",
                "EndpointID": "36598650abb0c25cde0da3442f587771a947f1c8b119f5455834b0d699fa82e1",
                "MacAddress": "02:42:ac:13:00:04",
                "IPv4Address": "172.19.0.4/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {
            "com.docker.compose.network": "default",
            "com.docker.compose.project": "startup",
            "com.docker.compose.version": "2.20.2"
        }
    }
]

docker ps shown below

CONTAINER ID   IMAGE                    COMMAND                  CREATED             STATUS         PORTS                    NAMES
fa9c94681ab1   startup-frontend-fligh   "docker-entrypoint.s…"   48 minutes ago      Up 4 seconds   0.0.0.0:3000->3000/tcp   startup-frontend-fligh-1
66759928be0a   startup-backend-flask    "flask run"              48 minutes ago      Up 5 seconds                            startup-backend-flask-1
1278a785f11c   redis:alpine             "docker-entrypoint.s…"   About an hour ago   Up 5 seconds   6379/tcp                 startup-redis-1
Tags:

2

Answers


  1. 0

    According to the output of docker compose ps command, your backend is listening on port 5000 which you have forwarded on port 8000 to the host. So you have to use either http://backend-flask:5000 or http://localhost:8000.

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  2. 0

    It is not a real solution but could you try with this docker-compose to check if it is just the DNS problem?

    version: '3'
    
services:
  backend-flask:
    build: ./backend  
  test-net:
      ipv4_address: 172.19.33.10


  frontend-fligh:
    build: ./frontend-fligh
    ports:
      - "3000:3000"
    depends_on:
      - backend-flask
    test-net:
      ipv4_address: 172.19.33.11
networks:
  test-net:
    ipam:
      driver: default
      config:
        - subnet: 172.19.33.0/24

    And change this too:

    const response = await fetch('http://172.19.33.10:5000/search', {
                    method: 'POST',
                    headers: {
                        'Content-Type': 'application/json'
                    },
                    body: JSON.stringify(query)
                });
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