Docker: Cannot connect to other container - docker

Question

docker-compose.yml
version: '3'
volumes:
wp-assets:
services:
mariadb:
build: ./requirements/mariadb
environment:
- MYSQL_ROOT_HOST=${MYSQL_ROOT_HOST}
- MYSQL_ROOT_PASSWORD=${MYSQL_ROOT_PASSWORD}
- MYSQL_DATABASE=${MYSQL_DATABASE}
- MYSQL_USER=${MYSQL_USER}
- MYSQL_PASSWORD=${MYSQL_PASSWORD}
ports:
- "127.0.0.1:3306:3306"
- "127.0.0.1:9999:9999" # test
wordpress:
environment:
- WORDPRESS_DB_HOST=${WORDPRESS_DB_HOST}
- WORDPRESS_DB_USER=${WORDPRESS_DB_USER}
- WORDPRESS_DB_PASSWORD=${WORDPRESS_DB_PASSWORD}
- WORDPRESS_DB_NAME=${WORDPRESS_DB_NAME}
- WORDPRESS_TABLE_PREFIX=${WORDPRESS_TABLE_PREFIX}
- WORDPRESS_AUTH_KEY=${WORDPRESS_AUTH_KEY}
- WORDPRESS_SECURE_AUTH_KEY=${WORDPRESS_SECURE_AUTH_KEY}
- WORDPRESS_LOGGED_IN_KEY=${WORDPRESS_LOGGED_IN_KEY}
- WORDPRESS_NONCE_KEY=${WORDPRESS_NONCE_KEY}
- WORDPRESS_AUTH_SALT=${WORDPRESS_AUTH_SALT}
- WORDPRESS_SECURE_AUTH_SALT=${WORDPRESS_SECURE_AUTH_SALT}
- WORDPRESS_LOGGED_IN_SALT=${WORDPRESS_LOGGED_IN_SALT}
- WORDPRESS_NONCE_SALT=${WORDPRESS_NONCE_SALT}
volumes:
- wp-assets:/var/wp-assets
build: ./requirements/wordpress
ports:
# host_port == 127.0.0.1:9000, allow only localhost
- "127.0.0.1:9000:9000"
nginx:
# image: nginx:latest
depends_on:
- wordpress
volumes:
- wp-assets:/var/wp-assets
build: ./requirements/nginx
ports:
# host_port == 0.0.0.0:8080, allow all interfaces
- "8080:80"
mariadb/Dockerfile
FROM debian:buster
# install mariadb-server
RUN apt update && apt install -y mariadb-server
# allow connection from wordpress (host name)
RUN sed -e 's/127.0.0.1/wordpress/' \
-i '/etc/mysql/mariadb.conf.d/50-server.cnf'
# used for socket
RUN mkdir -p /var/run/mysqld && \
chown -R mysql:mysql /var/lib/mysql /var/run/mysqld && \
chmod 777 /var/run/mysqld && \
touch /var/run/mysqld/mysqld.sock
# init db here
COPY docker-entrypoint.sh /
RUN chmod +x /docker-entrypoint.sh
#ENTRYPOINT ["/docker-entrypoint.sh"]
ENTRYPOINT ["tail", "-f"]
I was trying to connect mariadb with wordpress (mariadb-client), and got an error :
Can't connect to MySQL server on 'mariadb'
So I tested ports are good. But while other ports like nginx:80 or wordpress:9000 can be accessed by the other containers, ports of mariadb refuses connections.
I couldn't figure out what is difference between mariadb container and the others. What's the problem?

Answer 1

The ENTRYPOINT of your MariaDB Dockerfile is
ENTRYPOINT ["tail", "-f"]
so it doesn't actually run MariaDB.
You probably need to comment that out and comment back in
ENTRYPOINT ["/docker-entrypoint.sh"]

Answer 2

I was confused about ports. I thought that each containers could communicate by just opening ports, but there was no LISTENing ports. Docker-compose ports: just binds ports and has nothing to do with LISTEN.