Celery and Flask in same docker-compose

Question

I'm trying to use docker-compose to spawn my Flask/Celery/Redis services.

Here's my docker-compose.yml:

flask:
    build: .
    command: "python3 app.py"
    ports:
        - '5000:5000'
    links:
        - redis
    volumes:
        - .:/usr/src/app:ro

celery:
    build: .
    command: "celery -A app.celery worker --loglevel=info"
    volumes:
        - .:/usr/src/app:ro

redis:
    image: redis
    ports:
        - '6379:6379'

When I run this docker-compose, both Flask and Redis start fine and function as expected. Regarding Celery, Docker reports: flaskcelery_celery_1 exited with code 1, with no other info.

If I run my three services without Docker, and start Celery with celery -A app.celery worker --loglevel=info, my app functions just fine.

Some more info, if necessary:

Dockerfile: (this image installs requirements.txt on build as well)

FROM python:3.5-onbuild
EXPOSE 5000

requirements.txt:

flask==0.11.1
celery==3.1.23

docker-compose up output:

Starting flaskcelery_celery_1
Starting flaskcelery_redis_1
Starting flaskcelery_flask_1
Attaching to flaskcelery_celery_1, flaskcelery_redis_1, flaskcelery_flask_1
redis_1  |                 _._                                                  
redis_1  |            _.-``__ ''-._                                             
redis_1  |       _.-``    `.  `_.  ''-._           Redis 3.2.3 (00000000/0) 64 bit
redis_1  |   .-`` .-```.  ```\/    _.,_ ''-._                                   
redis_1  |  (    '      ,       .-`  | `,    )     Running in standalone mode
redis_1  |  |`-._`-...-` __...-.``-._|'` _.-'|     Port: 6379
redis_1  |  |    `-._   `._    /     _.-'    |     PID: 1
redis_1  |   `-._    `-._  `-./  _.-'    _.-'                                   
redis_1  |  |`-._`-._    `-.__.-'    _.-'_.-'|                                  
redis_1  |  |    `-._`-._        _.-'_.-'    |           http://redis.io        
redis_1  |   `-._    `-._`-.__.-'_.-'    _.-'                                   
redis_1  |  |`-._`-._    `-.__.-'    _.-'_.-'|                                  
redis_1  |  |    `-._`-._        _.-'_.-'    |                                  
redis_1  |   `-._    `-._`-.__.-'_.-'    _.-'                                   
redis_1  |       `-._    `-.__.-'    _.-'                                       
redis_1  |           `-._        _.-'                                           
redis_1  |               `-.__.-'                                               
redis_1  | 
redis_1  | 1:M 23 Aug 10:23:08.409 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
redis_1  | 1:M 23 Aug 10:23:08.409 # Server started, Redis version 3.2.3
redis_1  | 1:M 23 Aug 10:23:08.409 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
redis_1  | 1:M 23 Aug 10:23:08.409 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
redis_1  | 1:M 23 Aug 10:23:08.409 * The server is now ready to accept connections on port 6379
flaskcelery_celery_1 exited with code 1
flask_1  |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
flask_1  |  * Restarting with stat
flask_1  |  * Debugger is active!
flask_1  |  * Debugger pin code: 196-119-737

Answer 1

Solved my problem. I eventually figured out I could get a command prompt on the Docker image:

docker build -t <image name> .
docker run -it <image name> /bin/bash

Then trying to run celery within the container revealed the problem:

root@4a6edc5d7372:/usr/src/app# celery -A app.celery worker --loglevel=info
Running a worker with superuser privileges when the
worker accepts messages serialized with pickle is a very bad idea!

If you really want to continue then you have to set the C_FORCE_ROOT
environment variable (but please think about this before you do).

User information: uid=0 euid=0 gid=0 egid=0

Docker usually runs as root, and Celery doesn't like running as root for security reasons (I believe you can get code execution with pickle deserialization). The safer solution was to set the celery container to run as nobody. Working docker-compose.yml:

flask:
    build: .
    command: "python3 app.py"
    ports:
        - '5000:5000'
    links:
        - redis
        - celery
    volumes:
        - .:/usr/src/app:ro

celery:
    build: .
    command: "celery -A app.celery worker --loglevel=info"
    user: nobody
    links:
        - redis
    volumes:
        - .:/usr/src/app:ro

redis:
    image: redis
    ports:
        - '6379:6379'

Answer 2

if you dont want to deal with docker-compose and just want to use docker only this may be useful for you. First you need to create a "supervisord" file like below.

[supervisord]
nodaemon=true

[program:python]
stdout_logfile=/dev/stdout
stdout_logfile_maxbytes=0
stderr_logfile=/dev/stderr
stderr_logfile_maxbytes=0
command=python flask_api.py

[program:celeryworker]
stdout_logfile=/dev/stdout
stdout_logfile_maxbytes=0
stderr_logfile=/dev/stderr
stderr_logfile_maxbytes=0
command=celery -A flask_api worker -c 2

Then your docker file should look like this. Obviously this is just a template you can change it as you want.

FROM ubuntu:16.04
RUN apt-get update -y
RUN apt-get install -y python-pip python-dev build-essential libpq-dev git postgresql-9.5 postgresql-contrib
RUN apt-get install -y supervisor
RUN pip install --upgrade pip
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
WORKDIR /app
CMD ["supervisord"]

In this way, you can run the flask application and the celery worker in the same docker container.