How to connect the application container to the mysql containier - docker

Question

I am having an application service and a MySQL service but I am not able to connect the two containers and it keeps returning me this error
jango.db.utils.OperationalError: (2002, "Can't connect to MySQL server on '127.0.0.1' (115)")
I have included the links in my application service but nothing is working out.
Mine MySQL container is working up fine and even I can log into the MySQL container.
Here is the snapshot of the services:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
cc26d09a81d1 gmasmatrix_worker:latest "/entrypoint.sh /sta…" 17 seconds ago Exited (1) 11 seconds ago gmasmatrix_celeryworker_1
749f23c37b16 gmasmatrix_application:latest "/entrypoint.sh /sta…" 18 seconds ago Exited (1) 9 seconds ago gmasmatrix_application_1
666029ad063a gmasmatrix_flower "/entrypoint.sh /sta…" 18 seconds ago Exited (1) 10 seconds ago gmasmatrix_flower_1
50ac0497e66b mysql:5.7.10 "/entrypoint.sh mysq…" 21 seconds ago Up 17 seconds 0.0.0.0:3306->3306/tcp gmasmatrix_db_1
669fbbe0a81d mailhog/mailhog:v1.0.0 "MailHog" 21 seconds ago Up 18 seconds 1025/tcp, 0.0.0.0:8025->8025/tcp gmasmatrix_mailhog_1
235a46c8d453 redis:5.0 "docker-entrypoint.s…" 21 seconds ago Up 17 seconds 6379/tcp gmasmatrix_redis_1
Docker-compose file
version: '2'
services:
application: &application
image: gmasmatrix_application:latest
command: /start.sh
volumes:
- .:/app
# env_file:
# - .env
ports:
- 8000:8000
# cpu_shares: 874
# mem_limit: 1610612736
# mem_reservation: 1610612736
build:
context: ./
dockerfile: ./compose/local/application/Dockerfile
args:
- GMAS_ENV_TYPE=local
links:
- "db"
celeryworker:
<<: *application
image: gmasmatrix_worker:latest
depends_on:
- redis
- mailhog
ports: []
command: /start-celeryworker
links:
- "db"
flower:
<<: *application
image: gmasmatrix_flower
ports:
- "5555:5555"
command: /start-flower
links:
- "db"
mailhog:
image: mailhog/mailhog:v1.0.0
ports:
- "8025:8025"
redis:
image: redis:5.0
db:
image: mysql:5.7.10
environment:
MYSQL_DATABASE: gmas_mkt
MYSQL_ROOT_PASSWORD: pulkit1607
ports:
- "3306:3306"
``

Answer 1

Your application is trying to connect to 127.0.0.1 - which in docker points to the app container itself.
Instead you should use the IP of the db container. You can utilize the built-in docker DNS service to do this. In your application configuration, use db (the name of the mysql container) as the host to connect to instead of localhost or 127.0.0.1