Using the postgres image in a test - postgresql

Question

Given the following docker-compose.test.yml file:
version: '2'
services:
sut:
build: .
command: nosetests
environment:
- DJANGO_SETTINGS_MODULE=test.settings
links:
- db
db:
image: postgres
expose:
- 5432
Building the sut container
docker-compose -f docker-compose.test.yml build sut
Running the container:
thomas#linuxclientlobnek01:~/github/djlobnek$ docker-compose -f docker-compose.test.yml run sut /bin/bash
root#6694ec7148ac:/djlobnek# psql -h localhost -U postgres
psql: could not connect to server: Connection refused
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
**could not connect to server: Connection refused**
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?

Answer 1

It is possible that your application is attempting to connect to the database before the database is ready to accept connections. If this is the case, then implementing some sort of wait-for-the-database loop into the sut container can resolve the problem. I have in the past used something like:
while ! psql -h db -U postgres postgres -c 'select 1'; do
echo "waiting for database"
sleep 1
done
This is unnecessary if your application knows how to retry unsuccessful database connections.
Before you try this, it's a good idea to verify that the postgres container is actually functioning (e.g., by entering the sut container with docker exec and attempting to manually connect using psql).
Update
Trying to connect to localhost from inside the sut container won't work (postgres isn't run inside that container). You would need to use the hostname db, or you would need to the ip address of the db container. E.g:
postgres -h db -U postgres postgres
You could use localhost as the hostname if you docker exec into the db container itself.