Docker service intercommunication troubleshoot - mysql

Question

Attempting to dockerize a Symfony 3.1 application, I run Docker for Windows:
Docker Desktop Version: 2.0.0.3
Engine Version: 18.09.2
Compose Version: 1.23.2
Here is my current docker-compose.yaml:
version: "3.6"
services:
nginx:
build:
context: ./../..
dockerfile: ./docker/dev/nginx/Dockerfile
volumes:
- ./../..:/app
ports:
- 80:80
links:
- mariadb:mariadb
- php:php
php:
build:
context: ./../..
dockerfile: ./docker/dev/php/Dockerfile
volumes:
- ./../..:/app
links:
- mariadb:mariadb
mariadb:
build:
context: ./../..
dockerfile: ./docker/dev/mariadb/Dockerfile
volumes:
- database:/var/lib/mysql
ports:
- 3306:3306
environment:
- MYSQL_ROOT_PASSWORD=root
- MYSQL_DATABASE=todo_list
- MYSQL_USER=todo_list
- MYSQL_PASSWORD=todo_list
volumes:
database:
Here are my Dockerfiles for each of the 3 services above:
nginx:
FROM nginx:1.16.0-alpine
COPY docker/dev/nginx/config/nginx.conf /etc/nginx/conf.d/default.conf
COPY . /app
php:
FROM php:7.3.6-fpm-alpine3.10
RUN docker-php-ext-install -j$(nproc) pdo_mysql
COPY docker/dev/php/config/php.conf ${PHP_INI_DIR}/conf.d/default.ini
COPY . /app
mariadb:
FROM mariadb:10.3
COPY docker/dev/mariadb/config/mariadb.conf /etc/mysql/conf.d/default.cnf
RUN chmod 0444 /etc/mysql/conf.d/default.cnf
Running docker-compose up, everything seems fine, no inconsistencies or error/warning detected in the services logs…
The Symfony parameters.yml in which is defined database access and credentials looks like this:
parameters:
database_host: 127.0.0.1
database_port: 3306
database_name: todo_list
database_user: todo_list
database_password: todo_list
With this configuration I am able to run successfully the Symfony console commands:
php bin/console doctrine:schema:update
php bin/console doctrine:fixtures:load
Which means that in this context, the app has access to the database.
But when I interact with the app via HTTP (http://localhost in web browser), so via the docker service nginx, I get a SQLSTATE[HY000] [2002] Connection refused.
So I change the parameters:database_host entry in the parameters.yml from 127.0.0.1 to 172.31.0.1 (which is the current IP address of the mariadb container) and this time I can interact with the app via HTTP, without any problem for it to access to the database, but instead, I get a SQLSTATE[HY000] [2002] when attempting to access to the database via the Symfony console.
I suspected a Docker Compose misconfiguration but after checking and rechecking the Docker doc, tutorials, example GitHub repos, and similar SE questions, for hours, I don't get what I'd be doing wrong…

Answer 1

As #DavidMaze said in the comment, remove the links from the docker-compose file and use the name of the service instead of the address (mariadb instead of 127.0.0.1). This way it will work for connections coming from inside docker.
This way, as you have already seen, it stops working for connections coming from outside docker (neve used Symfony console but I assume it's outside of docker). To work around it you have at least two ways:
quick and dirty, add a line in your hosts file (on windows, the file should be at C:\Windows\System32\Drivers\etc) like
this: 127.0.0.1 mariadb, this will instruct windows to resolve
mariadb as 127.0.0.1
configure your project to use different config files depending on if you are connecting from inside or outside docker (can't tell you
exactly how, it really depends on your project structure)
IMHO option 1 is acceptable for development machines.

Answer 2

You can't use 127.0.0.1 in your parameter.yml but you can use 'mariadb' instead since you defined it in your links section.
Now links is described as deprecated so it will work but you'll probably want to go with networking.
version: "3.6"
services:
nginx:
build:
context: ./../..
dockerfile: ./docker/dev/nginx/Dockerfile
networks:
- frontend
- backend
volumes:
- ./../..:/app
ports:
- 80:80
php:
build:
context: ./../..
dockerfile: ./docker/dev/php/Dockerfile
networks:
- frontend
- backend
volumes:
- ./../..:/app
mariadb:
build:
context: ./../..
dockerfile: ./docker/dev/mariadb/Dockerfile
networks:
- backend
volumes:
- database:/var/lib/mysql
ports:
- 3306:3306
environment:
- MYSQL_ROOT_PASSWORD=root
- MYSQL_DATABASE=todo_list
- MYSQL_USER=todo_list
- MYSQL_PASSWORD=todo_list
volumes:
database:
networks:
frontend:
driver: bridge
name: frontend #or whatever custom name since 3.5
backend:
driver: bridge
name: backend #or whatever custom name since 3.5