Passing environment variable to docker image at build time with docker-compose

Question

Everything I tried following Dockerfile and docker compose references to pass an environment variable to the Docker image did not work.

I want to make this env var available during docker build when using docker-compose.

On the Docker host I have:

export BUILD_VERSION=1.0

app.js

console.log('BUILD_VERSION: ' + process.env.BUILD_VERSION);

Dockerfile:

FROM node
ADD app.js /
ARG BUILD_VERSION
ENV BUILD_VERSION=$BUILD_VERSION
RUN echo Build Time: $BUILD_VERSION
RUN node /app.js
CMD echo Run Time: $BUILD_VERSION

docker-compose.yml:

version: '3'
services:
  app:
    build:
      context: .
      args:
        - BUILD_VERSION

If I build the image directly, the env var is passed fine:

docker build -t test --no-cache --build-arg BUILD_VERSION .

and is also available at run-time:

$ docker run --rm test
Run Time: 1.0
$ docker run --rm test node /app
BUILD_VERSION: 1.0

but not with docker compose.

docker-compose up --build

...
Step 5/7 : RUN echo Build Time: $BUILD_VERSION
 ---> Running in 6115161f33bf
Build Time:
 ---> c691c619018a
Removing intermediate container 6115161f33bf
Step 6/7 : RUN node /app.js
 ---> Running in f51831cc5e1e
BUILD_VERSION:

It's only available at run-time:

$ docker run --rm test
Run Time: 1.0
$ docker run --rm test node /app
BUILD_VERSION: 1.0

I also tried using environment in docker-compose.yml like below which again only makes it available at run-time but not build-time:

version: '3'
services:
  app:
    build:
      context: .
    environment:
      - BUILD_VERSION

Please advise, how can I make it work in the least convoluted way?

Answer 1

Your example is working for me.

Have you tried deleting the images and building again? Docker won't re-build your image despite environment variables changed if the image is in cache.

You can delete them with:

 docker-compose down --rmi all

---

Edit, I show here how it is working for me at build time:

$ cat Dockerfile
FROM alpine
ARG BUILD_VERSION
ENV BUILD_VERSION=$BUILD_VERSION
RUN echo Build Time: $BUILD_VERSION

$ cat docker-compose.yml
version: '3'
services:
  app:
    build:
      context: .
      args:
        - BUILD_VERSION

Build:

$ export BUILD_VERSION=122221
$ docker-compose up --build
Creating network "a_default" with the default driver
Building app
Step 1/4 : FROM alpine
latest: Pulling from library/alpine
8e3ba11ec2a2: Pull complete
Digest: sha256:7043076348bf5040220df6ad703798fd8593a0918d06d3ce30c6c93be117e430
Status: Downloaded newer image for alpine:latest
---> 11cd0b38bc3c
Step 2/4 : ARG BUILD_VERSION
---> Running in b0a1a79967a0
Removing intermediate container b0a1a79967a0
---> 9fa331d63f6d
Step 3/4 : ENV BUILD_VERSION=$BUILD_VERSION
---> Running in a602c27689a5
Removing intermediate container a602c27689a5
---> bf2181423c93
Step 4/4 : RUN echo Build Time: $BUILD_VERSION                <<<<<< (*)
---> Running in 9d828cefcfab
Build Time: 122221
Removing intermediate container 9d828cefcfab
---> 2b3afa3d348c
Successfully built 2b3afa3d348c
Successfully tagged a_app:latest
Creating a_app_1 ... done
Attaching to a_app_1
a_app_1 exited with code 0

---

As the other answer mentioned, you can use docker-compose build --no-cache, and you can avoid mentioning "app" if you have multiple services, so docker-compose will build all the services. What you can do to handle different build versions in the same docker-compose build is to use different env vars, like:

$ cat docker-compose
version: '3'
services:
  app1:
    build:
      context: .
      args:
        - BUILD_VERSION=$APP1_BUILD_VERSION
  app2:
    build:
      context: .
      args:
        - BUILD_VERSION=$APP2_BUILD_VERSION

Export:

$ export APP1_BUILD_VERSION=1.1.1
$ export APP2_BUILD_VERSION=2.2.2

Build:

$ docker-compose build
Building app1
Step 1/4 : FROM alpine
latest: Pulling from library/alpine
8e3ba11ec2a2: Pull complete
Digest: sha256:7043076348bf5040220df6ad703798fd8593a0918d06d3ce30c6c93be117e430
Status: Downloaded newer image for alpine:latest
---> 11cd0b38bc3c
Step 2/4 : ARG BUILD_VERSION
---> Running in 0b66093bc2ef
Removing intermediate container 0b66093bc2ef
---> 906130ee5da8
Step 3/4 : ENV BUILD_VERSION=$BUILD_VERSION
---> Running in 9d89b48c875d
Removing intermediate container 9d89b48c875d
---> ca2480695149
Step 4/4 : RUN echo Build Time: $BUILD_VERSION
---> Running in 52dec27874ec
Build Time: 1.1.1
Removing intermediate container 52dec27874ec
---> 1b3654924297
Successfully built 1b3654924297
Successfully tagged a_app1:latest
Building app2
Step 1/4 : FROM alpine
---> 11cd0b38bc3c
Step 2/4 : ARG BUILD_VERSION
---> Using cache
---> 906130ee5da8
Step 3/4 : ENV BUILD_VERSION=$BUILD_VERSION
---> Running in d29442339459
Removing intermediate container d29442339459
---> 8b26def5ef3a
Step 4/4 : RUN echo Build Time: $BUILD_VERSION
---> Running in 4b3de2d223e5
Build Time: 2.2.2
Removing intermediate container 4b3de2d223e5
---> 89033b10b61e
Successfully built 89033b10b61e
Successfully tagged a_app2:latest

Answer 2

You need to set argument in docker-compose.yml as shown which will then be overriden to passed env variable -

version: '3'
services:
  app:
    build:
      context: .
      args:
        - BUILD_VERSION

Next export environment variable you need to pass.

$ export BUILD_VERSION=1.0

Now build the image using command

$ docker-compose build --no-cache --build-arg BUILD_VERSION=$BUILD_VERSION app