I am creating a Docker container for my umbrella app that so far contains just one phoenix API app.

This application has simply one DB table that is made of political parties, called “parties”.

when I run docker-compose up and visit http://localhost:4001/api/v1/parties I get the following error: ERROR 42P01 (undefined_table) relation "parties" does not exist

Obviously my table does not exists. However I do run my migrations in my Dockerfile:

# ./Dockerfile
# Elixir base image to start with
FROM elixir:1.8

# install hex package manager
RUN mix local.hex --force
RUN mix local.rebar --force

# install the latest Phoenix
RUN mix archive.install https://github.com/phoenixframework/archives/raw/master/phoenix_new.ez --force

# install NodeJS and NPM
RUN curl -sL https://deb.nodesource.com/setup_10.x -o nodesource_setup.sh
RUN bash nodesource_setup.sh
RUN apt-get install nodejs
RUN apt-get install -y inotify-tools

# create our app folder and copy our code in it and set it as default
RUN mkdir /app
COPY . /app
WORKDIR /app

# install dependencies
RUN mix deps.get
RUN mix deps.compile

# We can't separate the command as each command create a temporary container
# and each container as it own temporary variables

# run migrations
CMD mix ecto.migrate

# run phoenix server. The CMD is run each time the container is launched.
CMD mix phx.server

and here is my docker-compose.yml :

# the version of docker compose we use
version: '2'

services:
    # the first container will be called postgres
    postgres:
        # the image is the last official postgres image
        image: postgres
        # the volumes allow us to have a shared space between our computer and the docker vm
        volumes:
            - "./.data/postgres:/var/lib/postgresql"
         # set up environment variable for the postgres instance
        environment:
            POSTGRES_USER: ${PSQL_USER}
            POSTGRES_PASSWORD: ${PSQL_PWD}
            POOL: 100
        # the port to listen
        ports:
            - "5432:5432"
    # the second container is called redis
    redis:
        # the image is the last official redis image of the version 5
        image: redis:5
        ports:
            - "6379:6379"
        volumes:
            - ./.data/redis:/var/lib/redis
        # set up environment variable for the redis instance
        environment:
            REDIS_PASSWORD: ${REDIS_PWD}
    # our last container is called elixir
    elixir:
        # build use a path to a Dockerfile
        build: .
        # we set multiple ports as each of our application (but database) will use a different port
        ports:
            - "4001:4001"
            - "4101:4101"
        # we share the entire app with the container, but the libs
        volumes:
            - ".:/app"
            - "/app/deps"
            - "/app/apps/admin/assets/node_modules"
        # the container will not start if the postgres container isn't running
        depends_on:
            - postgres
        # set up environment variable for the phoenix instance
        environment:
            POSTGRES_USER: ${PSQL_USER}
            POSTGRES_PASSWORD: ${PSQL_PWD}
            POSTGRES_DB_TEST: ${PSQL_DB_TEST}
            POSTGRES_DB_DEV: ${PSQL_DB}
            POSTGRES_HOST: ${PSQL_HOST}

What is wrong with my code ?