This answer is for docker-compose version 2 and it also works on version 3
You can still access the data when you use depends_on.
If you look at docker docs Docker Compose and Django, you still can access the database like this:
version: '2'
services:
db:
image: postgres
web:
build: .
command: python manage.py runserver 0.0.0.0:8000
volumes:
- .:/code
ports:
- "8000:8000"
depends_on:
- db
What is the difference between links and depends_on?
links:
When you create a container for a database, for example:
docker run -d --name=test-mysql --env="MYSQL_ROOT_PASSWORD=mypassword" -P mysql
docker inspect d54cf8a0fb98 |grep HostPort
And you may find
"HostPort": "32777"
This means you can connect the database from your localhost port 32777 (3306 in container) but this port will change every time you restart or remove the container. So you can use links to make sure you will always connect to the database and don't have to know which port it is.
web:
links:
- db
depends_on:
I found a nice blog from Giorgio Ferraris Docker-compose.yml: from V1 to V2
When docker-compose executes V2 files, it will automatically build a network between all of the containers defined in the file, and every container will be immediately able to refer to the others just using the names defined in the docker-compose.yml file.
And
So we don’t need links anymore; links were used to start a network communication between our db container and our web-server container, but this is already done by docker-compose
Express dependency between services, which has two effects:
docker-compose up will start services in dependency order. In the following example, db and redis will be started before web.docker-compose up SERVICE will automatically include SERVICE’s dependencies. In the following example, docker-compose up web will also create and start db and redis.Simple example:
version: '2'
services:
web:
build: .
depends_on:
- db
- redis
redis:
image: redis
db:
image: postgres
Note: depends_on will not wait for db and redis to be “ready” before starting web - only until they have been started. If you need to wait for a service to be ready, see Controlling startup order for more on this problem and strategies for solving it.