Why isn't my PostgreSQL data persistent in Docker using volumes? - postgresql

Question

I am currently learning how to use Flask, PostgreSQL and Docker because I am trying to do a web app.
I have created two containers for the development phase: one for the database and other one for the web. The problem that I have is that whenever I stop and restart my containers, the data is not there anymore.
For the creation of the containers I have followed the following link: https://testdriven.io/blog/dockerizing-flask-with-postgres-gunicorn-and-nginx/#project-setup
I have seen that I could create a volume to persist the data in the container but it doesn't seem to work and I don't really understand why. Here is my docker-compose file:
version: '3.7'
services:
web:
build: ./services/web
restart: always
command: python manage.py run -h 0.0.0.0
volumes:
- ./services/web/:/usr/src/app/
- ./migrations:/usr/src/app/migrations
ports:
- 5000:5000
env_file:
- ./dev.env
depends_on:
- db
db:
container_name: postgres
restart: always
image: postgres:latest
volumes:
- pgdata:/var/lib/postgresql/data
- .:/usr/src/app #For refreshing the container if the code changes
ports:
- 5432:5432
environment:
- POSTGRES_USER=hello_flask
- POSTGRES_PASSWORD=hello_flask
- POSTGRES_DB= hello_flask_dev #To change
volumes:
pgdata:
I am careful to use docker-compose up -d so I don't remove any volume and the following volume is created seen with docker volume inspect:
[
{
"CreatedAt": "2021-04-19T13:19:05Z",
"Driver": "local",
"Labels": {
"com.docker.compose.project": "hera_docker",
"com.docker.compose.version": "1.29.0",
"com.docker.compose.volume": "pgdata"
},
"Mountpoint": "/var/lib/docker/volumes/hera_docker_pgdata/_data",
"Name": "hera_docker_pgdata",
"Options": null,
"Scope": "local"
}
]
I would like to maintain the docker-compose commands because the two containers are together in a multicontainer.
Any help will be of great help. I have checked some other questions in this forum but I don't really know what's going on that mine doesn't work.
Thanks in advance.

Answer 1

Well, after trying and trying and almost giving up, I found the solution. I will leave it here if it helps someone.
It appears that the "web" application was overwriting the database and the solution was to change in the docker-compose the depends_on: db in web to depends_on: web in db. Now, it looks like this:
version: '3.7'
services:
web:
build: ./services/web
restart: always
command: python manage.py run -h 0.0.0.0
volumes:
- ./services/web/:/usr/src/app/
ports:
- 5000:5000
env_file:
- ./dev.env
db:
container_name: postgres
restart: always
image: postgres:latest
volumes:
- "pgdata:/var/lib/postgresql/data"
- .:/usr/src/app
ports:
- 5432:5432
environment:
- POSTGRES_USER=hello_flask
- POSTGRES_PASSWORD=hello_flask
- POSTGRES_DB=hello_flask_dev
depends_on:
- web
volumes:
pgdata:
The change from pgdata:/var/lib/postgresql/data to "pgdata:/var/lib/postgresql/data" was just to not create a new folder in my flask directory.