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dockerdocker-compose

Cannot connect to docker compose network from host

I have two docker images. one is a postgresql database and the other is a FastAPI. I tried running both using docker run and it all works correctly. I can use 127.0.0.1:8000/docs and access the Swagger UI. The problem starts when using docker compose. Here my file:

services:
 
  db:
    image: postgres
    # restart: always
    environment:
      POSTGRES_USER: my-user
      POSTGRES_PASSWORD: password
    ports:
      - '5432:5432'
    volumes:
      - /var/lib/postgresql/data:/var/lib/postgresql/data

  api:
    image: api_rest
    # restart: always
    # links:
    #   - db
    extra_hosts:
      - "host.docker.internal:host-gateway"
    ports:
      - 8000:8000

The outputs seems Ok, as if both services are connecting. However, accessing 127.0.0.1:8000/docs gives nothing. I understood that using ports command should already expose the container IP with the host. Doing some debugging I did docker container inspect <MY FASTAPI CONTAINER ID> and got:

"Networks": {
                "network_default": {
                    "IPAMConfig": null,
                    "Links": null,
                    "Aliases": [
                        "api",
                        "b9201abec1c2"
                    ],
                    "MacAddress": "02:42:ac:15:00:03",
                    "NetworkID": "fbde8b8a0dc3ff02b24b9c59290dd7bb98256774c1e8e848beb577b77b7d7152",
                    "EndpointID": "00decc867548762ee60fa0db31c727fac80adf2fc5636060565ebaf5d64165b5",
                    "Gateway": "172.21.0.1",
                    "IPAddress": "172.21.0.3",
                    "IPPrefixLen": 16,
                    "IPv6Gateway": "",
                    "GlobalIPv6Address": "",
                    "GlobalIPv6PrefixLen": 0,
                    "DriverOpts": null,
                    "DNSNames": [
                        "fast-api-1",
                        "api",
                        "b9201abec1c2"
                    ]

I therefore try both 172.21.0.1 and 172.21.0.3 but no luck.

BTW: the output of docker compose is:

Attaching to fast-api-1, postgres-db-1
postgres-db-1   | 
postgres-db-1   | PostgreSQL Database directory appears to contain a database; Skipping initialization
postgres-db-1   | 
postgres-db-1   | 2024-03-27 15:47:30.892 UTC [1] LOG:  starting PostgreSQL 15.3 (Debian 15.3-1.pgdg110+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 10.2.1-6) 10.2.1 20210110, 64-bit
postgres-db-1   | 2024-03-27 15:47:30.892 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
postgres-db-1   | 2024-03-27 15:47:30.892 UTC [1] LOG:  listening on IPv6 address "::", port 5432
postgres-db-1   | 2024-03-27 15:47:30.907 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
postgres-db-1   | 2024-03-27 15:47:30.947 UTC [29] LOG:  database system was shut down at 2024-03-27 15:37:55 UTC
postgres-db-1   | 2024-03-27 15:47:30.973 UTC [1] LOG:  database system is ready to accept connections
fast-api-1  | INFO:     Will watch for changes in these directories: ['/']
fast-api-1  | INFO:     Loading environment from 'api_rest/docker.env'
fast-api-1  | INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
fast-api-1  | INFO:     Started reloader process [7] using WatchFiles
fast-api-1  | Connecting to database using postgresql+psycopg2://my-user:password@db:5432/postgres
fast-api-1  | INFO:     Started server process [9]
fast-api-1  | INFO:     Waiting for application startup.
fast-api-1  | INFO:     Application startup complete.

The output of docker ps

4eca35c35e45   api_rest      "/bin/sh -c 'uvicorn…"   About a minute ago   Up 3 seconds       0.0.0.0:8000->8000/tcp, :::8000->8000/tcp   fast-api-1
280b95fd9257   postgres-db   "docker-entrypoint.s…"   2 hours ago          Up 3 seconds       0.0.0.0:5432->5432/tcp, :::5432->5432/tcp   postgres-db-1

I tried changing port to 127.0.0.1:8000:8000 because is the IP I use on my web browser but no luck. Also, the command of extra_hosts I do not understand but it changes nothing.

Relevant information is:

  • I am running all un an Ubuntu Oracle VM (running on windows)
  • The VM does not have internet connection because of some proxy issues, etc. But as this seems all internal I thought it is nor relevant.
Solution

  • Your problem is visible here:

    fast-api-1  | INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

    Uvicorn is running with the socket bound to the default host 127.0.0.1, which is the localhost of the container, meaning that it will only accept traffic from within the container itself.

    See for example this page for a complete example, but in short you need to do something along the lines of the following:

    CMD ["uvicorn", "main:app", "--host", "0.0.0.0", ...]

    Using 0.0.0.0 as the host will accept traffic from outside of the container too.

    You should also just remove the extra_hosts, it's not needed. Then you should be able to connect from the host machine using 127.0.0.1:8000 just like that.