File writing failing in docker production environment - django

Question

In my production environments I am failing to write to files. For example, I've set up a test-task with Celery that writes the time to a file every minute:
#celery_app.task(name='print_time')
def print_time():
now = datetime.datetime.now().strftime('%Y %b %d %a #%H:%M')
cur_time = {"now": now}
print(f'The date and time sent: {cur_time}')
json.dump(cur_time, open(PATH.abspath(PATH.join(APP_DIR, "data", "cur_time.json")), "w"))
t = json.load(open(PATH.abspath(PATH.join(APP_DIR, "data", "cur_time.json"))))
print(f'The date and time received: {t}')
Both of the print statements will give the expected results, as of my writing this, they last printed:
The date and time sent: {'now': '2021 May 26 Wed #18:57'}
The date and time received: {'now': '2021 May 26 Wed #18:57'}
However, when I set up a view to display the contents:
class TimeView(TemplateView):
def get_context_data(self, **kwargs):
time = json.load(open(PATH.abspath(PATH.join(APP_DIR, "data", "cur_time.json"))))
return time
It becomes clear that the file is not really updating in the development environment when i go to the url and the time continues to remain the same as it was when I originally rsynced the file from my development environment (which is successfully updating the file contents)
To verify this further I've also ran cat cur_time.json and stat cur_time.json to verify that the files are not being written to successfully.
Knowing that the files are not being updated, my question is two-fold. One, why are my print statements in the celery task printing the results as if the files are being updated? Two, what is the most likely cause and solution for this problem?
I was thinking it had to do with my Docker containers file writing permissions but I changed the write permissions in the data directory already by running chmod -R 777 data. Also, I haven't received any permission error messages which seem to be thrown when permissions are the issue at hand. I'm starting to hit the limits of my knowledge and wondering if anyone has any idea what the problem/solution could be. Thank you
Edit in response to comments:
I am using docker-compose. Here is my production.yml file:
version: '3'
volumes:
production_postgres_data: {}
production_postgres_data_backups: {}
production_traefik: {}
services:
django: &django
build:
context: .
dockerfile: ./compose/production/django/Dockerfile
image: myapp_production_django
depends_on:
- postgres
- redis
env_file:
...
command: /start
postgres:
...
traefik:
...
redis:
image: redis:5.0
celeryworker:
<<: *django
image: myapp_production_celeryworker
command: /start-celeryworker
celerybeat:
<<: *django
image: myapp_production_celerybeat
command: /start-celerybeat
flower:
<<: *django
image: myapp_production_flower
command: /start-flower
Second edit in response to comments:
Here is a view of my local.yml file
version: '3'
volumes:
local_postgres_data: {}
local_postgres_data_backups: {}
services:
django: &django
build:
context: .
dockerfile: ./compose/local/django/Dockerfile
image: myapp_local_django
container_name: django
depends_on:
- postgres
volumes:
- .:/app:z
env_file:
...
ports:
- "8000:8000"
command: /start
postgres:
build:
context: .
dockerfile: ./compose/production/postgres/Dockerfile
image: myapp_production_postgres
container_name: postgres
volumes:
- local_postgres_data:/var/lib/postgresql/data:Z
- local_postgres_data_backups:/backups:z
env_file:
...
redis:
image: redis:5.0
container_name: redis
celeryworker:
<<: *django
image: myapp_local_celeryworker
container_name: celeryworker
depends_on:
- redis
- postgres
ports: []
command: /start-celeryworker
celerybeat:
<<: *django
image: myapp_local_celerybeat
container_name: celerybeat
depends_on:
- redis
- postgres
ports: []
command: /start-celerybeat
flower:
<<: *django
image: myapp_local_flower
container_name: flower
ports:
- "5555:5555"
command: /start-flower

Answer 1

To give credit where it is due. The problem and solution were elegantly put forward by #IainShelvington in the comments above.
Reason for problem: "Any files you write in a docker container will not be written to the host machine unless you mount a volume and write to that volume."
Solution for problem: "Add a new volume to the global "volumes:" in your compose config. Mount that volume in the "django" service, all the celery services inherit from that service so it should be shared. Write and read the files from the location that you mounted (this should be completely different from the app mount, like "/celery-logs" or something)"
To demonstrate what this solution would look like in my specific example, I added the following to my production.yml file:
volumes:
...
production_celery: {}
services:
django: &django
build:
...
image: myapp_production_django
depends_on:
...
volumes:
- production_celery:/app/celerydata:z
env_file:
...
command: /start
Then, all data files derived from my celery scripts were sent to and pulled from the new volume/directory titled "celerydata"
As mentioned in the comments, my app had previously been dependent on APScheduler and I had grown accustomed to quickly writing datafiles to the host machine and being able to peek through them with ease. To once again view them on the host machine and as a safety precaution (data redundancy), I started using the following command sequences to copy the files from the celerydata directory into my local machine where i can look through them with the added ease of a graphic interface:
docker ps # note container_id == ${CID} below
export CID=foobarbaz123
docker cp ${CID}:/app/celerydata ./celery_storage
At some point in the future I might make that into a script to run when starting up the container and will update the answer accordingly.