I’m having trouble demonstrating that data I generate on a shared volume is persistent, and I can’t figure out why. I have a very simple docker-compose file:

version: "3.9"

# Define network
networks:
    sorcernet:
        name: sorcer_net

# Define services
services:
    preclean:
        container_name: cleaner
        build:
            context: .
            dockerfile: DEESfile
        image: dees
        networks:
            - sorcernet
        volumes:
            - pgdata:/usr/share/appdata
        #command: python run dees.py

    process:
        container_name: processor
        build:
            context: .
            dockerfile: OASISfile
        image: oasis
        networks:
            - sorcernet
        volumes:
            - pgdata:/usr/share/appdata

volumes:
    pgdata:
        name: pgdata

Running the docker-compose file to keep the containers running in the background:

vscode ➜ /com.docker.devenvironments.code $ docker compose up -d
[+] Running 4/4
 ⠿ Network sorcer_net   Created
 ⠿ Volume "pgdata"      Created
 ⠿ Container processor  Started
 ⠿ Container cleaner    Started

Both images are running:

vscode ➜ /com.docker.devenvironments.code $ docker image ls
REPOSITORY      TAG          IMAGE ID       CREATED          SIZE
oasis          latest      e2399b9954c8    9 seconds ago   1.09GB
dees           latest      af09040befd5   31 seconds ago   1.08GB

and the volume shows up as expected:

vscode ➜ /com.docker.devenvironments.code $ docker volume ls
DRIVER    VOLUME NAME
local     pgdata```

Running the docker container, I navigate to the volume folder. There’s nothing in the folder — this is expected.

vscode ➜ /com.docker.devenvironments.code $ docker run -it oasis
[[email protected] opt]# cd /usr/share/appdata/
[[email protected] appdata]# ls
[[email protected] appdata]# 

Since there’s nothing in the folder, I create a file in called “dog.txt” and recheck the folder contents. The file is there. I exit the container.

[[email protected] appdata]# touch dog.txt
[[email protected] appdata]# ls
dog.txt
[[email protected] appdata]# exit
exit

To check the persistence of the data, I re-run the container, but nothing is written to the volume.

vscode ➜ /com.docker.devenvironments.code $ docker run -it oasis
[[email protected] opt]# cd /usr/share/appdata/
[[email protected] appdata]# ls
[[email protected] appdata]# 

What gives? I’ve tried defining the volume as persistent, and I know each of the images have a folder location at /usr/share/appdata.