Docker-Compose binding volumes, file sharing issue - docker

Question

I am new to docker and had a problem that hope you could help.
I have defined multiple services (HTTPSERV, IMED, etc...) in my docker-compose file and these services have a python code inside and a docker file for running them. The dockerfile also copies the required files into a host path defined in docker-compose. The HTTPSERV and IMED must share a text file and expose it to an external user sending a GET request to HTTPSERV.
In docker-compose I have defined a local host directory and bind it to a named volume. The services and docker files are meant to share each service files and run.
As soon as I run the docker-compose, the files related to the first service copies files in the PATH directory where "src" and change the permission right of the "src" folder not letting the other services copy their files. This causes the next services to fail to find the appropriate files and the whole orchestration process fails.
version: "3.9"
networks:
default:
ipam:
config:
- subnet: 172.28.0.2/20
services:
httpserv:
user: root
container_name: httpserver
build: ./HTTPSERV
volumes:
- myapp:/httpApp:rw
networks:
default:
ipv4_address: 172.28.0.5
ports:
- "8080:3000"
rabitQ:
user: root
container_name: rabitQ
image: rabbitmq:3.8-management
networks:
default:
ipv4_address: 172.28.0.4
ports:
- "9000:15672"
imed:
user: root
container_name: IMED-Serv
build: ./IMED
volumes:
- myapp:/imed:rw
networks:
- default
# restart: on-failure
orig:
user: root
container_name: ORIG-Serv
build: ./ORIG
volumes:
- myapp:/orig:rw
networks:
- default
# restart: on-failure
obse:
container_name: OBSE-Serv
build: ./OBSE
volumes:
- myapp:/obse:rw
networks:
- default
# restart: on-failure
depends_on:
- "httpserv"
links:
- httpserv
volumes:
myapp:
driver: local
driver_opts:
type: none
o: bind
device: /home/dockerfiles/hj/a3/src
The content of the docker file is similar for most of the services and is as follow:
FROM python:3.8-slim-buster
WORKDIR /imed
COPY . .
RUN pip install --no-cache-dir -r imed-requirements.txt
RUN chmod 777 ./imed.sh
CMD ["./imed.sh"]
The code has root access and the UserID and GroupID are set
I also used the anonymously named volumes but the same issue happens.

Answer 1

In Docker it's often better to avoid "sharing files" as a first-class concept. Imagine running this in a clustered system like Kubernetes; if you have three copies of each service, and they're running in a cloud of a hundred systems, "sharing files" suddenly becomes difficult.
Given the infrastructure you've shown here, you have a couple of straightforward options:
Add an HTTP endpoint to update the file. You'd need to protect this endpoint in some way, since you don't want external callers accessing it; maybe filter it in an Nginx reverse proxy, or use a second HTTP server in the same process. The service that has the updated content would then call something like
r = requests.post('http://webserv/internal/file.txt', data=contents)
r.raise_for_status()
Add an HTTP endpoint to the service that owns the file. When the Web server service starts up, and periodically after that, it makes a request
r = requests.get('http://imed/file.txt')
You already have RabbitMQ in this stack; add a RabbitMQ consumer in a separate thread, and post the updated file content to a RabbitMQ topic.
There's some potential trouble with the "push" models if the Web server service restarts, since it won't be functional until the other service sends it the current version of file.
If you really do want to do this with a shared filesystem, I'd recommend creating a dedicated directory and dedicated volume to do this. Do not mount a volume over your entire application code. (It will prevent docker build from updating the application, and in the setup you've shown, you're mounting the same application-code volume over every service, so you're running four copies of the same service instead of four different services.)
Adding in the shared volume, but removing a number of other unnecessary options, I'd rewrite the docker-compose.yml file as:
version: '3.9'
services:
httpserv:
build: ./HTTPSERV
ports:
- "8080:3000"
volumes:
- shared:/shared
rabitQ:
image: rabbitmq:3.8-management
hostname: rabitQ # (RabbitMQ specifically needs this setting)
ports:
- "9000:15672"
imed:
build: ./IMED
volumes:
- shared:/shared
orig:
build: ./ORIG
obse:
build: ./OBSE
depends_on:
- httpserv
volumes:
shared:
I'd probably have the producing service unconditionally copy the file into the volume on startup, and have the consuming service block on it being present. (Don't depend on Docker to initialize the volume; it doesn't work on Docker bind mounts, or on Kubernetes, or if the underlying image has changed.) So long as the files are world-readable the two services' user IDs don't need to match.