如何从命令行连接到在非默认端口上的 Docker 容器中运行的 Postgres？

Question

I am new to Docker, and even after reading several similar questions on Stack Overflow do not really understand what I need to do to connect to Postgres using psql via the command line. My Postgres container is running on port 6432, mapped to the default port of 5432 (I changed the default port because I also have the Postgres desktop app running with other databases on port 5432).

I have tried psql -p 6432 but I keep getting this error: psql: error: could not connect to server: No such file or directory . I then tried psql -h localhost -p 6432 -U root , and was prompted to put in the password for the root user, which failed even though I input the correct password and produced this error: psql: error: FATAL: database "root" does not exist . I know that my Postgres container is running because I can see it running in the Docker desktop app.

Here is my docker-compose.yml file:

version: '3'

networks: 
    my_test_app:

services: 

    # nginx
    nginx-service:
        image: nginx:stable-alpine
        container_name: nginx-container
        ports: 
            - "8080:80"
        volumes: 
            - ./app:/var/www/project
            - ./nginx/default.conf:/etc/nginx/conf.d/default.conf
        depends_on: 
            - php-service
            - postgres-service
        networks: 
            - my_test_app 
  
    # php
    php-service:
        image: php:7.4-fpm-alpine
        container_name: php-container
        ports:
            - "9000:9000"
        working_dir: /var/www/project
        volumes:
            - ./app:/var/www/project
        networks: 
            - my_test_app  

    # postgres
    postgres-service:
        image: postgres:alpine
        container_name: postgres-container
        ports: 
            - "6432:5432"
        volumes: 
            - ./postgres:/var/lib/postgresql/data
        restart: always
        environment: 
            POSTGRES_USER: root
            POSTGRES_PASSWORD: secret
            POSTGRES_DB: db_my_test_app
        networks: 
            - my_test_app

...and my nginx config file (I have no idea if this is relevant):

server {

    listen 80;
    index index.php index.html index.htm;
    server_name localhost;
    root /var/www/project/public;

    location / {
        try_files $uri $uri/ =404;
    }

    location ~ \.php$ {
        try_files $uri =404;
        fastcgi_split_path_info ^(.+\.php)(/.*)$;
        fastcgi_pass php-service:9000;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
        fastcgi_param DOCUMENT_ROOT $realpath_root;
    }
}

I appreciate any help you may be able to offer me. By the way, is there any way that I can view and edit the databases (create/alter tables, etc.) I create in this container using a service like Postico?

Answer 1

I think the problem is that you're trying to connect to a different database than the one that actually exists.

You specify an environment variable in your config:

POSTGRES_DB: db_my_test_app

When this postgres container starts up and finds an empty data directory, it creates a database for you. It determines the name of that new database based on a few checks. In order:

1. What is the value of $POSTGRES_DB , if it is set
2. What is the value of `$POSTGRES_USER, if it is set
3. If nothing else, call it 'postgres'

When psql connects to postgres, it has to connect to a database. Unless a different one is specified, it tries to connect to a database with the same name as the user that is connecting.

Given your command: psql -h localhost -p 6432 -U root , psql will try and connect to a database called root . When it finds that this database doesn't exist, it prints the following:

❯ psql -h localhost -p 6432 -U root
Password for user root:
psql: error: FATAL:  database "root" does not exist

If we specify a database name to match the one that's configured in your docker-compose configuration, we get the following:

✖2 ❯ psql -h localhost -p 6432 -U root -d db_my_test_app
Password for user root:
psql (13.2)
Type "help" for help.

db_my_test_app=#

Your quick fix is to specify -d <database_name> when you try to connect.

If you'd like to change the name of this database, the bit about "postgres creates a database only if it finds an empty data directory" becomes important: since you specify a docker volume ./postgres:/var/lib/postgresql/data , your database files will be persisted between docker compose sessions and you'll need to delete the ./postgres directory on your host machine to clear it out and create a new one.

As an aside, since your initial question states that psql is unable to connect to postgres, I think it'll be helpful to show what that error message looks like as well:

❯ psql -h localhost -p 9876
psql: error: could not connect to server: Connection refused
        Is the server running on host "localhost" (::1) and accepting
        TCP/IP connections on port 9876?
could not connect to server: Connection refused
        Is the server running on host "localhost" (127.0.0.1) and accepting
        TCP/IP connections on port 9876?