How to use volume in docker compose for postgres? - postgresql

Question

Here is the image I am using.
I named it posgres_test
If I run the image individually
docker run -i -t -v="test_volume:/var/lib/postgresql" -p 5432:5432 posgres_test
I can access it with
psql -h 192.168.99.100 -p 5432 -U pguser -W pgdb
Or I can access it with my golang app
// host is set to postgres
db, err := sql.Open("postgres", "postgres://pguser:pguser#postgres:5432/pgdb")
// table test_db is manually created.
rows, err := db.Query("SELECT name FROM test_db WHERE)
However if I use docker compose
docker-compose.yml
version: "2"
services:
postgres:
image: my_image/postgresql:9.3
volumes:
- test_volume:/var/lib/postgresql
ports:
- "5432:5432"
web:
image: my-golang-app4
ports:
- "8080:8080"
volumes:
test_volume: {}
I get the following
pguser#pgdb ERROR: relation "test_db" does not exist at character 15
I know for sure test_db exist in test_volume since
docker run -i -t -v="test_volume:/var/lib/postgresql" -p 5432:5432 posgres_test
psql -h 192.168.99.100 -p 5432 -U pguser -W pgdb
\dt
will show the table I created
But it seems like my app in docker compose cannot find it
Can someone help me out?

Answer 1

About your docker-compose file
First, I thought it's because you don't use the 'links' option to link your postgres container to the web container - it's good practice if you don't expand ports - but you expand postgres port.
If you want to use inheritance from the image you posted
Instead of using this line:
my_image/postgresql:9.3
use:
docker/postgres
and create path docker/postgres and there place Dockerfile with inheritance from the container you want.
I always use shared volumes in docker-compose.yml like this:
.:/var/www/html
where . is my project path where I place my code files.
Image I created to test this case
I don't have all your docker files structure to reproduce this error and fix it, so I created a docker-compose, which should match your needs or help to fix your issue:
version: '2'
services:
web:
build: docker/web
ports:
- "8080:8080"
links:
- dbpostgres
volumes:
- .:/var/www/html # I will share my code so I map this path
dbpostgres:
image: postgres
volumes:
- /private/var/lib/postgresql:/var/lib/postgresql
ports:
- "5432:5432"
environment:
POSTGRES_USER: pguser
POSTGRES_PASSWORD: pguser
POSTGRES_DB: pgdb
Notes:
I will recommend use official postgres image
I left comments next to the lines.
How I made connection:
host=dbpostgres port=5432 dbname=pgdb user=pguser password=pguser
Because my web container knows host dbpostgres (image name and domain name) now - I link them using links.
If you need database from existing container
If you need the database from your existing container just use the docker option cp to copy database locally:
docker cp posgres_test:/var/lib/postgresql /private/var/lib/postgresql
where /private/var/lib/postgresql is a path on your localhost.
You also need to change credentials to db in docker-compose to your old credentials.
You have to do it before running docker-compose because if db doesn't exist, it will be created.
Any questions, let me know.

Answer 2

If the volume is external and already existing before the use of docker-compose you should declare it external, or else docker compose will create a new volume with the project name as prefix.
volumes:
test_volume:
external: true
Docs for external using compose v3 (mostly similar to v2): https://docs.docker.com/compose/compose-file/compose-file-v3/#external

Answer 3

I think it sould be something like this for you.
docker run -itd -p 5432:5432 --name postgres_test -v /path/in/your/host :/path/in/your/container postgres_test psql -h 192.168.99.100 -p 5432 -U pguser -W pgdb
Read Docker docs(https://docs.docker.com/engine/tutorials/dockervolumes/), watch tutorials (there is a Docker Youtube channel whith great tutorials).