How to use volume in docker compose for postgres?

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

1. Firstly I thought it's because you don't use 'links' option to link your postgres container to web container - it's good practice if you don't expand ports - but you expand postgres port.

2. If you want 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 inharitance from container you want.

3. I always use sharing 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 your all docker files structure to reproduce this error and fix it, so I created 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:

1. I will recommend use official postgres image

2. 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 know host dbpostgres(image name and domain name) now - I link them using links.

If you need database from existing container

If you need database from your existing container just use option docker cp to copy database localy:

docker cp posgres_test:/var/lib/postgresql /private/var/lib/postgresql 

where /private/var/lib/postgresql is path on your localhost. You need also change credentials to db in docker-compose to your old credentials. You have to do it before run docker-compose because if db doesn't exist, will be crated.

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