README.md

C++ Gradle gcc Docker example

Clone this repository with git clone https://github.com/danial-k/docker-intro.git and open docker-intro/gradle in an ide.

Alternatively, to skip cloning and use these instructions directly, create a new directory for this example:

mkdir -p docker-intro/gradle
cd docker-intro/gradle

Create a Gradle container to generate a new project:

docker run \
-it \
--name gradle \
--hostname gradle \
--mount type=bind,src=`pwd`/app,dst=/app \
-w //app \
gradle:5.4-jdk8 \
bash

Initialise a new C++ project with Gradle and accept the default project name (app):

gradle init --type cpp-application --dsl groovy

At this point, the project source files should be visible in the app folder in your IDE, the application entrypoint is located at app/src/main/cpp/app.cpp.

In a separate terminal window, create a new gcc container to compile the project:

docker run \
-it \
--name gcc \
--hostname gcc \
--mount type=bind,src=`pwd`/app,dst=/app \
-w //app \
gcc:9.1 \
bash

This container does not contain a Java runtime (required by gradle), install with:

apt-get update
apt-get install openjdk-8-jre -y

In the gcc container build the application:

./gradlew build

Verify the output:

./build/exe/main/debug/app

Although the application is functional, the current state is not optimised for production because of the added build tooling. To view the modifications to the original base image, in a new terminal window run docker diff gcc. The following section will deploy the compiled application to run on a suitable base image.

Building deployment container

To publish the application as a self-contained image with a Debian base image, use the Dockerfile for this project (placed outside the app directory):

docker build -t gradle-gcc:1.0.0 .

This will send all files in the current directory to the Docker daemon's build context (excluding paths specified in .dockerignore), then create and tag the image. Note that the build context is ~ 350 KB with the specified exlusions, without which the context would increase to ~ 900 KB. Once the image has been built, run with:

docker run gradle-gcc:1.0.0

The built application should then execute and terminate, followed by container shut down.