Can't to connect to postgres container - docker

Question

I define postgres server in docker-compose.yml:
db:
image: postgres:9.5
expose:
- 5432
Then in another docker container I tried to connect to this postgres container. But it gives an error with warning:
Is the server running on host "db" (172.22.0.2) and accepting
data-service_1 | TCP/IP connections on port 5432?
Why container can't to connect to another by provided information (host="db" and port=5432)?
PS
Full docker-compose.yml:
version: "2"
services:
data-service:
build: .
depends_on:
- db
ports:
- "50051:50051"
db:
image: postgres:9.5
depends_on:
- data-volume
environment:
- POSTGRES_USER=cobrain
- POSTGRES_PASSWORD=a
- POSTGRES_DB=datasets
ports:
- "8000:5432"
expose:
- 5432
volumes_from:
- data-volume
# - container:postgres9.5-data
restart: always
data-volume:
image: busybox
command: echo "I'm data container"
volumes:
- /var/lib/postgresql/data

Answer 1

Solution #1. Same file.
To be able to access the db container, you have to define your other containers in context of docker-compose.yml. When containers are started, each container gets all other containers mapped in /etc/hosts.
Just do
version: '2'
services:
web:
image: your/image
db:
image: postgres:9.5
If you do not wish to put your other containers into the same docker-compose.yml, there are other solutions:
Solution #2. IP
Do docker inspect <name of your db container> and look for IPAddress directive in the result listing. Use that IPAddress as host to connect to.
Solution #3. Networks
Make your containers join same network. For that, under each service, define:
services:
db:
networks:
- myNetwork
Don't forget to change db for each container you are starting.
I usually go with the first solution during development. I use apache+php as one container and pgsql as another one, a separate DB for every project. I do not start more than one setting of docker-compose.yml, so in this case defining both containers in one .yml config is perfect.

Answer 2

the depends on is not correct. i would try to use other paramters like LINKS and environment:
version: "2"
services:
data-service:
build: .
links:
- db
ports:
- "50051:50051"
volumes_from: ["db"]
environment:
DATABASE_HOST: db
db:
image: postgres:9.5
environment:
- POSTGRES_USER=cobrain
- POSTGRES_PASSWORD=a
- POSTGRES_DB=datasets
ports:
- "8000:5432"
expose:
- 5432
#volumes_from:
#- data-volume
# - container:postgres9.5-data
restart: always
data-volume:
image: busybox
command: echo "I'm data container"
volumes:
- /var/lib/postgresql/data
this one works for me (not postgres but mysql)