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I have docker compose app running wordpress, phpmyadmin, mysql on my development system. I successfully created the database and was able to initialize wordpress. When I click on the login link after initializing wordpress I see "Error establishing a database connection".

It seems like all I can find when searching are actual problems connecting to the database. I believe I'm connecting to the database successfully, but something happens a bit downstream which is causing the error.

The wordpress container can indeed connect to the database, but throws the error after DESCRIBE wp_users is executed. Or at least that's the last item in the mysql log. Also note phpmyadmin can connect to the database with the credentials wordpress and the password in /run/secrets/appdb-password (see docker-compose.yml).

I set up the wordpress username password as lou.king password, but it seems that would be irrelevant.

It might be relevant that I'm accessing wordpress using a port, i.e., via http://dev.localhost:8010/wp-login.php

Below are the mysql log after SET GLOBAL general_log = 'ON';, and relevant queries. This is what happens when accessing the wp-login.php view (or any other view, of course).

2025-02-17T12:18:55.580518Z        82 Connect   [email protected] on  using TCP/IP
2025-02-17T12:18:55.580861Z        82 Query     SET NAMES utf8mb4
2025-02-17T12:18:55.581354Z        82 Query     SET NAMES 'utf8mb4' COLLATE 'utf8mb4_unicode_520_ci'
2025-02-17T12:18:55.581499Z        82 Query     SELECT @@SESSION.sql_mode
2025-02-17T12:18:55.581706Z        82 Query     SET SESSION sql_mode='NO_ZERO_IN_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION'
2025-02-17T12:18:55.582140Z        82 Init DB   wordpress
2025-02-17T12:18:55.583342Z        82 Query     SELECT option_name, option_value FROM wp_options WHERE autoload IN ( 'yes', 'on', 'auto-on', 'auto' )
2025-02-17T12:18:55.584121Z        82 Query     DESCRIBE wp_users
2025-02-17T12:18:55.585367Z        82 Quit
^C



sh-5.1# mysql -u wordpress -p************ wordpress
mysql: [Warning] Using a password on the command line interface can be insecure.
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 85
Server version: 8.0.40 MySQL Community Server - GPL

Copyright (c) 2000, 2024, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> describe wp_users;
+---------------------+-----------------+------+-----+---------------------+----------------+
| Field               | Type            | Null | Key | Default             | Extra          |
+---------------------+-----------------+------+-----+---------------------+----------------+
| ID                  | bigint unsigned | NO   | PRI | NULL                | auto_increment |
| user_login          | varchar(60)     | NO   | MUL |                     |                |
| user_pass           | varchar(255)    | NO   |     |                     |                |
| user_nicename       | varchar(50)     | NO   | MUL |                     |                |
| user_email          | varchar(100)    | NO   | MUL |                     |                |
| user_url            | varchar(100)    | NO   |     |                     |                |
| user_registered     | datetime        | NO   |     | 0000-00-00 00:00:00 |                |
| user_activation_key | varchar(255)    | NO   |     |                     |                |
| user_status         | int             | NO   |     | 0                   |                |
| display_name        | varchar(250)    | NO   |     |                     |                |
+---------------------+-----------------+------+-----+---------------------+----------------+
10 rows in set (0.00 sec)

mysql> select * from wp_users;
+----+------------+------------------------------------+---------------+-----------------------------+----------+---------------------+---------------------+-------------+--------------+
| ID | user_login | user_pass                          | user_nicename | user_email                  | user_url | user_registered     | user_activation_key | user_status | display_name |
+----+------------+------------------------------------+---------------+-----------------------------+----------+---------------------+---------------------+-------------+--------------+
|  1 | lou.king   | $P$BkSsVsE9aF0ZmWfPT8YYy4jKGh5Co41 | lou-king      | [email protected]        | http:    | 2025-02-16 18:43:16 |                     |           0 | lou.king     |
+----+------------+------------------------------------+---------------+-----------------------------+----------+---------------------+---------------------+-------------+--------------+
1 row in set (0.00 sec)

I'm not sure this is relevant, but here's the docker-compose.yml file

# see .env for image version env variables
# see repo/settings/environments for image version env variables for github actions
services:
  wordpress:
    image: wordpress:${WORDPRESS_VER}-php${PHP_VER}-fpm-alpine
    restart: always
    depends_on:
      - db
    networks:
      - backend-network
      - frontend-network
    secrets:
      - appdb-password
    volumes:
      - wordpress:/var/www/html
      - ${VAR_LOG_HOST}:/var/log
    environment:
      TZ: ${TZ}
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_NAME: wordpress
      WORDPRESS_DB_PASSWORD_FILE: /run/secrets/appdb-password
      WORDPRESS_DEBUG: ${WORDPRESS_DEBUG}

  db:
    # https://github.com/docker-library/mysql/issues/275#issuecomment-636831964
    image: mysql:${MYSQL_VER}
    # # changed in mysql 8.4
    # command: --mysql-native-password=ON
    # command: '--default-authentication-plugin=mysql_native_password'
    command: '--default-authentication-plugin=mysql_native_password --log_error_verbosity=3' # mysql
    restart: always
    secrets:
      - root-password
      - appdb-password
    volumes:
      - db:/var/lib/mysql
      - ${VAR_LOG_HOST}:/var/log
    networks:
      - backend-network
    environment:
      TZ: ${TZ}
      MYSQL_ROOT_PASSWORD_FILE: /run/secrets/root-password
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wordpress
      MYSQL_PASSWORD_FILE: /run/secrets/appdb-password

  web:
    image: louking/${APP_NAME}-web:${APP_VER}
    build: 
      context: web
      args:
        - NGINX_VER=${NGINX_VER}
        - PHPMYADMIN_VER=${PHPMYADMIN_VER}
    restart: always
    networks:
      - frontend-network
    volumes:
      - ${VAR_LOG_HOST}:/var/log
    environment:
      TZ: ${TZ}
    ports:
      - ${APP_PORT}:80
    # uncomment to debug
    # command: [nginx-debug, '-g', 'daemon off;']

  phpmyadmin:
    image: phpmyadmin:${PHPMYADMIN_VER}-fpm
    restart: always
    depends_on:
      - db
    networks:
      - backend-network
      - frontend-network
    volumes:
      - ${VAR_LOG_HOST}:/var/log
    environment:
      TZ: ${TZ}
      PMA_ABSOLUTE_URI: http://phpmyadmin/phpmyadmin/

volumes:
  db:
  wordpress:

secrets:
  root-password:
    file: config/db/root-password.txt
  appdb-password:
    file: config/db/appdb-password.txt

networks:
  backend-network:
  frontend-network:
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2 Answers 2

Reset to default
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Ensure database connection details in wp-config.php match the MySQL container setting:

define( 'DB_NAME', 'database_name_here' );

/** Database username */ define( 'DB_USER', 'username_here' );

/** Database password */ define( 'DB_PASSWORD', 'password_here' );

/** Database hostname */ define( 'DB_HOST', 'localhost' )

DB_HOST should match the service name in docker-compose.yml.

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  • thanks. but as mentioned the connection is getting established but fails trying to DESCRIBE wp_users. actually I think this is a problem with my nginx configuration which I didn't show. I'll answer the question with how I corrected the issue. Commented Feb 18 at 19:57
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It looks like there was a problem with my nginx.conf which I hadn't posted. I am able to connect just fine using the wordpress apache image.

# see .env for image version env variables
# see repo/settings/environments for image version env variables for github actions
services:
  wordpress:
    image: wordpress:${WORDPRESS_VER}-php${PHP_VER}-apache
    restart: always
    depends_on:
      - db
    ports:
      - ${APP_PORT}:80
    networks:
      - backend-network
      - frontend-network
    secrets:
      - appdb-password
    volumes:
      - wordpress:/var/www/html
      - ${VAR_LOG_HOST}:/var/log
    environment:
      TZ: ${TZ}
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_NAME: wordpress
      WORDPRESS_DB_PASSWORD_FILE: /run/secrets/appdb-password
      WORDPRESS_DEBUG: ${WORDPRESS_DEBUG}

  db:
    # https://github.com/docker-library/mysql/issues/275#issuecomment-636831964
    image: mysql:${MYSQL_VER}
    # # changed in mysql 8.4
    # command: --mysql-native-password=ON
    # command: '--default-authentication-plugin=mysql_native_password'
    command: '--default-authentication-plugin=mysql_native_password --log_error_verbosity=3' # mysql
    restart: always
    secrets:
      - root-password
      - appdb-password
    volumes:
      - db:/var/lib/mysql
      - ${VAR_LOG_HOST}:/var/log
    networks:
      - backend-network
    environment:
      TZ: ${TZ}
      MYSQL_ROOT_PASSWORD_FILE: /run/secrets/root-password
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wordpress
      MYSQL_PASSWORD_FILE: /run/secrets/appdb-password

volumes:
  db:
  wordpress:

secrets:
  root-password:
    file: config/db/root-password.txt
  appdb-password:
    file: config/db/appdb-password.txt

networks:
  backend-network:
  frontend-network:

for completeness, here is the nginx.conf file which didn't seem to work

events { }
# uncomment to debug
# error_log /var/log/nginx/error.log debug;

http {
    include mime.types;

    # see https://github.com/sjmf/reverse-proxy-minimal-example
    map $http_x_forwarded_proto $real_scheme {
        default $scheme;
        https "https";
    }

    map $http_host $port {
        default $server_port;
        "~^[^\:]+:(?<p>\d+)$" $p;
    }

    server {
        listen       80;
        root /usr/share/nginx/html;
        index index.php index.html index.htm;

        # use web server for static files, requires copy from phpadmin in web/Dockerfile
        location ~* ^/phpmyadmin/.+\.php$ {
            # try_files $uri $uri/ =404;

            root /var/www/html;
            rewrite ^/phpmyadmin(/.*)$ $1 break; # https://stackoverflow.com/a/47447211/799921
            fastcgi_pass phpmyadmin:9000;
            include fastcgi.conf;

            # replace these with forwarded versions
            fastcgi_param   REMOTE_ADDR             $http_x_forwarded_for;
            fastcgi_param   REMOTE_PORT             $http_x_forwarded_port;
            fastcgi_param   SERVER_ADDR             $http_x_forwarded_for;
            fastcgi_param   SERVER_PORT             $http_x_forwarded_port;
            fastcgi_param   HTTP_HOST               $http_x_forwarded_host;

            fastcgi_param   HTTPS                   $http_x_forwarded_scheme;
        }

        location ~ \.php$ {
            # try_files $uri $uri/ =404;

            # fpm listens to port 9000 per https://linux.die.net/man/8/php-fpm
            # fpm uses fastcgi per https://www.nginx.com/resources/wiki/start/topics/examples/fastcgiexample/
            root /var/www/html;
            fastcgi_pass wordpress:9000;
            include fastcgi.conf;

            # replace these with forwarded versions
            fastcgi_param   REMOTE_ADDR             $http_x_forwarded_for;
            fastcgi_param   REMOTE_PORT             $http_x_forwarded_port;
            fastcgi_param   SERVER_ADDR             $http_x_forwarded_for;
            fastcgi_param   SERVER_PORT             $http_x_forwarded_port;
            fastcgi_param   HTTP_HOST               $http_x_forwarded_host;

            fastcgi_param   HTTPS                   $http_x_forwarded_scheme;
        }
    }

    include /etc/nginx/conf.d/*.conf;
}
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