pcewing/docker-incremental-compile-demo

Demonstration of incremental C/C++ compilation in Docker

Incremental Builds in Docker

This repository demonstrates one way to accomplish incrementally compiling and packaging a C/C++ application in Docker. Premake is used in this demo to automatically generate makefiles that support incremental compilation.

Concepts

Rather than having a single Docker image, we use a multistage build to create three:

• myapp-base : A base image that contains the dependencies that are shared between build-time and run-time
• myapp-builder : An image based on the myapp-base image that also contains all build dependencies for compiling and linking the MyApp application, such as library headers and the GCC toolchain
• myapp : An image based on the myapp-base image that also contains all run-time dependencies of MyApp, such as the creation of the non-root user the application should be run as

The general workflow will be:

• Build the base and builder images
  • We can build just these two images by specifying a target when executing our first docker image build command
• Use the builder image to compile and link the MyApp application
  • By passing in the working directory as a volume, we can effectively extract all of the build artifacts back to the host
• Build the myapp image
  • Copy in the pre-built artifacts via the ADD directive

Walkthrough

First, build the builder image which will also implicitly build the base image:

docker image build -t myapp-builder --target myapp-builder .

Remove any pre-existing build directory on the host:

rm -rf ./build

Use the builder image to compile the application:

docker container run \
    -u $(id -u):$(id -g) \
    -v $(pwd):/workspace \
    -w /workspace \
    myapp-builder \
    sh -c './premake.sh && cd build && make'

Ensure the build directory now exists and the artifacts in it have the correct ownership:

ls -la ./build

Try running the same command as before to build the application:

docker container run \
    -u $(id -u):$(id -g) \
    -v $(pwd):/workspace \
    -w /workspace \
    myapp-builder \
    sh -c './premake.sh && cd build && make'

If no changes were made to the main.cpp file, you should notice in the output that it is not recompiled. Try making a change to main.cpp and running the command again.

Once the application is built, bake it into a docker container image by building the myapp image:

docker image build -t myapp --target myapp .

Finally, verify that we can run the myapp container image:

docker container run myapp