docker-compose down not persisting postgresql data

Question

My docker-compose file:

version: '3'

services:
  app:
    container_name: application
    build: .cloud/php
    image: app-application
    depends_on:
      - pgres
    ports:
      - "9050:9000"
    volumes:
      - ./:/var/www:cached
    networks:
      - application_network

  nginx:
    container_name: application.nginx
    image: nginx
    ports:
      - "8050:8000"
    volumes:
      - .cloud/nginx/nginx.conf:/etc/nginx/conf.d/default.conf:cached
      - ./:/var/www:cached
    depends_on:
      - app
    networks:
      - application_network

  pgres:
    container_name: application.postgres
    image: postgres
    restart: always
    ports:
      - "54325:5432"
    environment:
      POSTGRES_DB: application
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: example
      PGDATA: /tmp
    volumes:
      - .cloud/postgres/data:/var/lib/postgresql/data
    networks:
      - application_network
networks:
  application_network:
    driver: bridge

When I run docker-compose down, postgresql data is not persisting and database resets completely. I tried to put the postgresql volume into its own /postgresql/data folder but still same result. What am I missing here?

I think it has to do something with the way you're using PGDATA. If you don't understand it, I would remove it. On Docker Hub they're suggesting to define it as a subdirectory of /var/lib/postgresql/data. I also looked at the docker-entrypoint.sh but didn't quite understand how they're using that env variable. — Stefan Golubović
– Stefan Golubović, Commented Mar 26, 2020 at 19:46
Perhaps, the other thing you could try is .cloud/postgres/data:/tmp instead of .cloud/postgres/data:/var/lib/postgresql/data. — Stefan Golubović
– Stefan Golubović, Commented Mar 26, 2020 at 19:52

Jeff Schaller · Accepted Answer · 2023-11-21 11:53:04Z

The problem is here

    environment:
      PGDATA: /tmp
    volumes:
      - .cloud/postgres/data:/var/lib/postgresql/data

With the PGDATA env var, you are setting the cluster data directory explicitly. So, what it does is, once you start your container (e.g. via docker-compose up), Postgres server will persist your db data as per your PGDATA setting within the /tmp directory. On the other hand you are mounting a different path in the container (/var/lib/postgresql/data) instead of the /tmp path. Thus once you run docker-compose down, the container and the persisted data in /tmp will be gone for good, since /tmp is not set as mounting point. So, unless you really need to do so, you better not touch it at all.

A working configuration might look so (shortened for the sake of brevity):

version: '3'
services:
  pgres:
    image: "postgres" # use latest official postgres version or a specific version e.g. postgres:10.12
    volumes:
      - .cloud/postgres/:/var/lib/postgresql/data/ # persist data even if container shuts down

Another thing is, even let's say you configured it via PGDATA like so

    environment:
      PGDATA: /tmp
    volumes:
      - .cloud/postgres/data:/tmp

It wouldn't be a good idea, since the path /tmp is in your case, as the name tmp (temporary) suggests, really not reliable. docker-compose down will probably not affect it at all, but on the next boot, i.e. once you run docker-compose up again, the underlying OS (Linux) will very much likely delete the content of the directory /tmp, therefore the mounted local dir .cloud/postgres/data will be also immediately emptied and your persisted data will be gone. In any case the /tmp dir is somewhat managed by Linux, thus the data saved there might simply disappear any time - so don't rely on it!

Teşekkürler, PGDATA env kaldırınca çalıştı :) For the future readers, removing PGDATA from env solves the problem.

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