wordpress "error establishing a database connection" after setup

Question

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: 

Answer 1

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.

Answer 2

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; }