Dockerfile if else condition with external arguments
There is an interesting alternative to the proposed solutions, that works with a single Dockerfile, require only a single call to docker build per conditional build and avoids bash.
Solution:
The following Dockerfile
solves that problem. Copy-paste it and try it yourself.
ARG my_arg
FROM centos:7 AS base
RUN echo "do stuff with the centos image"
FROM base AS branch-version-1
RUN echo "this is the stage that sets VAR=TRUE"
ENV VAR=TRUE
FROM base AS branch-version-2
RUN echo "this is the stage that sets VAR=FALSE"
ENV VAR=FALSE
FROM branch-version-${my_arg} AS final
RUN echo "VAR is equal to ${VAR}"
Explanation of Dockerfile:
We first get a base
image (centos:7
in your case) and put it into its own stage. The base
stage should contain things that you want to do before the condition. After that, we have two more stages, representing the branches of our condition: branch-version-1
and branch-version-2
. We build both of them. The final
stage than chooses one of these stages, based on my_arg
. Conditional Dockerfile. There you go.
Output when running:
(I abbreviated this a little...)
my_arg==2
docker build --build-arg my_arg=2 .
Step 1/12 : ARG my_arg
Step 2/12 : ARG ENV
Step 3/12 : FROM centos:7 AS base
Step 4/12 : RUN echo "do stuff with the centos image"
do stuff with the centos image
Step 5/12 : FROM base AS branch-version-1
Step 6/12 : RUN echo "this is the stage that sets VAR=TRUE"
this is the stage that sets VAR=TRUE
Step 7/12 : ENV VAR=TRUE
Step 8/12 : FROM base AS branch-version-2
Step 9/12 : RUN echo "this is the stage that sets VAR=FALSE"
this is the stage that sets VAR=FALSE
Step 10/12 : ENV VAR=FALSE
Step 11/12 : FROM branch-version-${my_arg}
Step 12/12 : RUN echo "VAR is equal to ${VAR}"
VAR is equal to FALSE
my_arg==1
docker build --build-arg my_arg=1 .
...
Step 11/12 : FROM branch-version-${my_arg}
Step 12/12 : RUN echo "VAR is equal to ${VAR}"
VAR is equal to TRUE
Thanks to Tõnis for this amazing idea!
Do not use build args described in other answers where at all possible. This is an old messy solution. Docker's target property solves for this issue.
Target Example
Dockerfile
FROM foo as base
RUN ...
# Build dev image
FROM base as image-dev
RUN ...
COPY ...
# Build prod image
FROM base as image-prod
RUN ...
COPY ...
docker build --target image-dev -t foo .
version: '3.4'
services:
dev:
build:
context: .
dockerfile: Dockerfile
target: image-dev
Real World
Dockerfiles get complex in the real world. Use buildkit & COPY --from
for faster, more maintainable Dockerfiles:
- Docker builds every stage above the target, regardless of whether it is inherited or not. Use buildkit to build only inherited stages. Docker must by v19+. Hopefully this will be a default feature soon.
- Targets may share build stages. Use
COPY --from
to simplify inheritance.
FROM foo as base
RUN ...
WORKDIR /opt/my-proj
FROM base as npm-ci-dev
# invalidate cache
COPY --chown=www-data:www-data ./package.json /opt/my-proj/package.json
COPY --chown=www-data:www-data ./package-lock.json /opt/my-proj/package-lock.json
RUN npm ci
FROM base as npm-ci-prod
# invalidate cache
COPY --chown=www-data:www-data ./package.json /opt/my-proj/package.json
COPY --chown=www-data:www-data ./package-lock.json /opt/my-proj/package-lock.json
RUN npm ci --only=prod
FROM base as proj-files
COPY --chown=www-data:www-data ./ /opt/my-proj
FROM base as image-dev
# Will mount, not copy in dev environment
RUN ...
FROM base as image-ci
COPY --from=npm-ci-dev /opt/my-proj .
COPY --from=proj-files /opt/my-proj .
RUN ...
FROM base as image-stage
COPY --from=npm-ci-prod /opt/my-proj .
COPY --from=proj-files /opt/my-proj .
RUN ...
FROM base as image-prod
COPY --from=npm-ci-prod /opt/my-proj .
COPY --from=proj-files /opt/my-proj .
RUN ...
Enable experimental mode.
sudo echo '{"experimental": true}' | sudo tee /etc/docker/daemon.json
Build with buildkit enabled. Buildkit builds without cache by default - enable with --build-arg BUILDKIT_INLINE_CACHE=1
CI build job.
DOCKER_BUILDKIT=1 \
docker build \
--build-arg BUILDKIT_INLINE_CACHE=1 \
--target image-ci\
-t foo:ci
.
Use cache from a pulled image with --cache-from
Prod build job
docker pull foo:ci
docker pull foo:stage
DOCKER_BUILDKIT=1 \
docker build \
--cache-from foo:ci,foo:stage \
--target image-prod \
-t prod
.
It might not look that clean but you can have your Dockerfile (conditional) as follow:
FROM centos:7
ARG arg
RUN if [[ -z "$arg" ]] ; then echo Argument not provided ; else echo Argument is $arg ; fi
and then build the image as:
docker build -t my_docker . --build-arg arg=45
or
docker build -t my_docker .