I am trying to create configuration for several environments with a single Dockerfile
, several docker-compose
files and several envoronment_variables
files. I need it to use a different file with python dependencies for each environment.
Let's say, we create a web
service in two environments: development
and production
. To achieve this, I create the following file structure:
docker-compose-dev.yml
docker-compose-prod.yml
envs/
dev.env
prod.env
web/
Dockerfile
requirements_dev.txt
requirements_prod.txt
The objective is to instantiate the proper name of a requirements_*.txt
file in the Dockerfile
during the container's build
process. According to the documentation, I tried this naïve approach, which doesn't seem to work:
REQUIREMENTS=requirements_dev.txt
REQUIREMENTS=requirements_prod.txt
Use this environment variable in the Dockerfile:
FROM python:3.5
ENV PYTHONUNBUFFERED 1
ENV APP_ROOT /usr/src/app
...
COPY $REQUIREMENTS $APP_ROOT/
RUN pip install -r $APP_ROOT/$REQUIREMENTS
Import the corresponding definition in a docker-compose
configuration:
version: '2'
services:
web:
build: ./web
env_file:
- envs/dev.env # in docker-compose-dev.yml
- envs/prod.env # in docker-compose-prod.yml
...
When I run docker-compose up --build docker-compose-dev.yml
, the $REQUIREMENTS
variable is not defined at the build process.
In the docker-compose
documentation there is a note on this:
Note: If your service specifies a build option, variables defined in environment files will not be automatically visible during the build. Use the args sub-option of build to define build-time environment variables.
But to use the ARG
option in the Dockerfile
, like ARG REQUIREMENTS
, one needs a corresponding args
option in docker-compose
, like this:
services:
web:
build:
context: ./web
args:
- REQUIREMENTS
Nevertheless, with this configuration my tests also failed, because, according to the documentation, the value of the REQUIREMENTS
variable in Dockerfile is taken from
the environment where Compose is running
Therefore, it takes value from my shell, but not from envs/dev.env
.
So my question is:
Is it possible to pass environment variable from
env_file
indocker-compose
toDockerfile
at build time without setting variables locally in my shell?
Your docker-compose.yml should look like this:
version: '2'
services:
web:
build:
context: ./web
args:
REQUIREMENTS: "requirements_dev.txt"
Your Dockerfile should define the build-argument using ARG
like this:
FROM python:3.5
ENV PYTHONUNBUFFERED 1
ENV APP_ROOT /usr/src/app
ARG REQUIREMENTS
...
COPY $REQUIREMENTS $APP_ROOT/
RUN pip install -r $APP_ROOT/$REQUIREMENTS
I validated this and created a minified functional demo at Github: