How do I run migrations in Dockerized Django?

Question

I followed a Docker + Django tutorial which was great, in that I could successfully build and run the website following the instructions. However, I can't for the life of me figure out how to successfully run a database migration after changing a model.

Here are the steps I've taken:

1. Clone the associated git repo

2. Set up a virtual machine called dev

   • with docker-machine create -d virtualbox dev
   • and point to it with eval $(docker-machine env dev)

3. Built and started it up with:

   • docker-compose build
   • and docker-compose up -d

4. Run initial migration (the only time I'm able to run a migration that appears successful):

   • docker-compose run web python manage.py migrate

5. Checked that the website works by navigating to the IP address returned by:

   • docker-machine ip dev

6. Make a change to a model. I just added this to the Item model in web/docker_django/apps/todo/models.py file.:

   • name = models.CharField(default='Unnamed', max_length=50, null=False)

7. Update the image and restart the containers with:

   • docker-compose down --volumes
   • then docker-compose build
   • then docker-compose up --force-recreate -d

Migration attempt number 1:

I used:

docker-compose run web python manage.py makemigrations todo

Then:

docker-compose run web python manage.py migrate

After the makemigrations command, it said:

Migrations for 'todo':
  0001_initial.py:
    - Create model Item

When I ran the migrate command, it gave the following message:

Operations to perform: 
  Synchronize unmigrated apps: messages, todo, staticfiles 
  Apply all migrations: contenttypes, admin, auth, sessions 
Synchronizing apps without migrations: 
  Creating tables... 
    Running deferred SQL... 
  Installing custom SQL... 
Running migrations: 
  No migrations to apply. 

So that didn't work.

Migration attempt number 2:

This time I tried running migrations from directly inside the running web container. This looked like this:

(macbook)$ docker exec -it dockerizingdjango_web_1 bash
root@38f9381f179b:/usr/src/app# ls
Dockerfile  docker_django  manage.py  requirements.txt  static  tests
root@38f9381f179b:/usr/src/app# python manage.py makemigrations todo
Migrations for 'todo':
  0001_initial.py:
    - Create model Item
root@38f9381f179b:/usr/src/app# python manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: staticfiles, messages
  Apply all migrations: contenttypes, todo, admin, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states... DONE
  Applying todo.0001_initial...Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/django/db/backends/utils.py", line 62, in execute
    return self.cursor.execute(sql)
psycopg2.ProgrammingError: relation "todo_item" already exists

Moreover, I couldn't find any migrations folders in that container.

I clearly have very little idea what's happening under the hood here, so if someone could show me how to successfully change models and run database migrations I would much appreciate it. Bonus points if you can help me conceptualize what's happening where when I run these commands that have to get the web and postgres images to work together.

EDIT: What worked for me

@MazelTov's suggestions will all be helpful for automating the process as I get more used to developing with Docker, but the thing I was missing, that @MazelTov filled me in on in a very helpful discussion, was mounting so that migrations show up in my local machine.

So basically, my Migration Attempt 1 would have worked just fine if instead of, for example:

docker-compose run web python manage.py makemigrations todo

...I used:

docker-compose run --service-ports -v $(pwd)/web:/usr/src/app web python manage.py makemigrations todo

Answer 1

There are many ways how to achieve this.

1) Run ./manage.py migrate before you start your app (uwsgi, runserver,...) in bash script

Dockerfile

FROM debian:latest

...

# entrypoint, must be executable file chmod +x entrypoint.sh
COPY entrypoint.sh /home/docker/entrypoint.sh

# what happens when I start the container
CMD ["/home/docker/entrypoint.sh"]

entrypoint.sh

#!/bin/bash

./manage.py collectstatic --noinput
# i commit my migration files to git so i dont need to run it on server
# ./manage.py makemigrations app_name
./manage.py migrate

# here it start nginx and the uwsgi
supervisord -c /etc/supervisor/supervisord.conf -n

2) If you have a lot of migration files and you dont want any downtime, you could run the migrate command from seperate docker-compose service

docker-compose.yml

version: '3.3'

services:  

  # starts the supervisor (uwsgi + nginx)
  web:
    build: .
    ports: ["80:80"]

  # this service will use same image, and once the migration is done it will be stopped
  web_migrations:
    build: .
    command: ./manage.py migrate