Dockerize project to build, test and run the game

Create a [Dockerfile][1] with [multi-stage building][2] to create
a build environment based on the [Gradle Docker image][3] and
a lightweight runner environment based on the [Eclipse Temurin
Docker image][4] (both based on OpenJDK 17).

Create a .dockerignore file based on .gitignore to skip files that
[should not be uploaded in the docker image][5].

Create a [docker-compose.yml][6] to setup four services:
- `game` to run the app for end users.
- `linter` to run all linters once.
- `tester` to rerun all tests with live reload.
- `demo` to rerun the app with live reload.

Add the same image name to [build the docker image only once][7] for
multiple services sharing with the same codebase.

Create a .env file to [configure environment variables][8] used inside
the compose file. Add the [`COMPOSE_PROJECT_NAME` variable][9] to assign
a prefix for all resources managed by compose.

Update the pre-commit config to use `docker compose` with the `linter`
image instead of raw `docker` commands to speed up the execution.

Update the README.md to use `docker compose` instead of raw `docker`
commands to execute tasks related to the project.

[1]: https://docs.docker.com/engine/reference/builder/
[2]: https://docs.docker.com/develop/develop-images/multistage-build/
[3]: https://hub.docker.com/_/gradle
[4]: https://hub.docker.com/_/eclipse-temurin
[5]: https://codefresh.io/docker-tutorial/not-ignore-dockerignore-2/
[6]: https://docs.docker.com/compose/compose-file/
[7]: https://stackoverflow.com/questions/40899236/how-to-prevent-docker-compose-building-the-same-image-multiple-times
[8]: https://docs.docker.com/compose/environment-variables/
[9]: https://docs.docker.com/compose/reference/envvars/#compose_project_name

.dockerignore

@@ -0,0 +1,10 @@
+# Ignore Git files
+.git
+.gitignore
+.gitattributes
+
+# Ignore Gradle project-specific cache directory
+.gradle
+
+# Ignore Gradle build output directory
+build

.env

@@ -0,0 +1,4 @@
+COMPOSE_PROJECT_NAME=galaxy-raiders
+
+GALAXY_RAIDERS_IMAGE=galaxy-raiders
+GALAXY_RAIDERS_VERSION=dev

.pre-commit-config.yaml

@@ -15,6 +15,6 @@ repos:
     name: Run Kotlin linters
     description: This hook runs Gradle to execute linters
     language: system
-    entry: bash -c "docker container run --rm --user gradle --volume $PWD:/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle --no-daemon formatKotlin detekt"
+    entry: docker compose --profile dev run -T --rm linter
     types: [kotlin]
     pass_filenames: false

Dockerfile

@@ -0,0 +1,62 @@
+################################################################################
+#                                  BASE IMAGE                                  #
+################################################################################
+
+# Use Gradle image to run Gradle commands
+FROM gradle:7.4.2-jdk17 AS base
+
+# Set default docker build args
+ARG APP_DIR=/home/gradle/galaxy-raiders
+
+# Change default workdir
+WORKDIR ${APP_DIR}
+
+# Set environment variable to disable Gradle Daemon
+ENV GRADLE_OPTS=-Dorg.gradle.daemon=false
+
+# Give the ownership of workdir to the Gradle user
+RUN chown -R gradle:gradle .
+
+# Change to non-priviled user (PID 1000)
+USER gradle
+
+# NOTE: This repo has gradle wrappers to ensure developers use the same version
+# of gradle in every environment. However, using gradle's docker image already
+# guarantees that. Therefore, commands below can use the `gradle` CLI directly.
+
+# Copy source code to workdir
+COPY --chown=gradle:gradle . .
+
+# NOTE: Gradle download dependencies only when they are necessary, which slows
+# tasks the first time they execute. Running them here will allow docker to
+# cache these dependencies to speed up containers that execute gradle tasks.
+
+# Force gradle to download dependencies to build, lint and test code
+RUN gradle --no-build-cache clean
+
+################################################################################
+#                                BUILDER IMAGE                                 #
+################################################################################
+
+# Use base image to build the project
+FROM base AS builder
+
+# Use gradle wrapper to generate an uber JAR
+RUN gradle --no-daemon shadowJar
+
+################################################################################
+#                               PRODUCTION IMAGE                               #
+################################################################################
+
+# Use Eclipse Temurin image to run the project
+FROM eclipse-temurin:17-jdk AS runner
+
+# Reuse default docker build args
+ARG APP_DIR=/home/gradle/galaxy-raiders
+
+# Copy runtime from image
+COPY --from=builder ${APP_DIR}/app/build/libs/galaxy-raiders.jar \
+                    /bin/runner/galaxy-raiders.jar
+
+# Run uber JAR to start application
+CMD ["java", "-jar", "galaxy-raiders.jar"]

README.md

@@ -30,19 +30,22 @@ pre-commit run --all-files
 
 Alternatively, to execute the linters manually, run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle --no-daemon formatKotlin detekt
+docker compose --profile dev run --rm linter
 ```
 
 ## Compilation
 
-To compile all classes in the project, run:
+The compilation of all classes and the generation of a runnable self-contained
+JAR is made "behind the scenes" by [docker][4].
+
+To build the development images, run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle --no-daemon clean assemble
+docker compose --profile dev build
 ```
 
-To generate a runnable self-contained JAR of the project, run:
+To build the production images, run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle --no-daemon clean shadowJar
+docker compose --profile prod build
 ```
 
 ## Tests
@@ -51,32 +54,31 @@ All tests in the project are developed using [JUnit 5][8].
 
 To execute all tests (with live reload), run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle --continuous test
+docker compose --profile dev up tester
 ```
 
 ## Execution
 
 To execute the project in development mode (with live reload), run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle --continuous run
+docker compose --profile dev up demo --build
 ```
 
-To execute the project in production mode, generate a runnable self-contained
-JAR of the project, then run:
+To execute the project in production mode, run:
 ```bash
-docker container run --rm --volume "$PWD"/app/build/libs/galaxy-raiders.jar:/bin/runner/galaxy-raiders.jar --workdir /bin/runner eclipse-temurin:17-jdk java -jar galaxy-raiders.jar
+docker compose --profile prod up game --build
 ```
 
 ## Other tasks
 
 To find available gradle tasks, run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle tasks
+docker compose --profile dev run --rm demo gradle --no-daemon tasks
 ```
 
 To execute any task, run:
 ```bash
-docker container run --rm --user gradle --volume "$PWD":/home/gradle/app --workdir /home/gradle/app gradle:7.4.2-jdk17 gradle {task}
+docker compose --profile dev run --rm demo gradle --no-daemon {task}
 ```
 
 [1]: https://uspdigital.usp.br/jupiterweb/obterDisciplina?sgldis=MAC0218

docker-compose.yml

@@ -0,0 +1,48 @@
+services:
+  # The `game` service is the production app for end users.
+  game:
+    image: "${GALAXY_RAIDERS_IMAGE}:${GALAXY_RAIDERS_VERSION}"
+    build:
+      context: .
+      target: "runner"
+    profiles:
+      - "prod"
+
+  # The `linter` service allows running all linters.
+  # Whenever a file changes, Gradle will rerun detekt and ktlint.
+  linter:
+    image: "${GALAXY_RAIDERS_IMAGE}:${GALAXY_RAIDERS_VERSION}"
+    build:
+      context: .
+      target: "base"
+    command: "gradle formatKotlin detekt"
+    volumes:
+      - "./:/home/gradle/galaxy-raiders/"
+    profiles:
+      - "dev"
+
+  # The `tester` service allows running all tests.
+  # Whenever a file changes, JUnit will rerun all tests related to it.
+  tester:
+    image: "${GALAXY_RAIDERS_IMAGE}:${GALAXY_RAIDERS_VERSION}"
+    build:
+      context: .
+      target: "base"
+    command: "gradle --continuous test"
+    volumes:
+      - "./:/home/gradle/galaxy-raiders/"
+    profiles:
+      - "dev"
+
+  # The `demo` service allows running the application.
+  # Whenever a file changes, the app will be restarted automatically.
+  demo:
+    image: "${GALAXY_RAIDERS_IMAGE}:${GALAXY_RAIDERS_VERSION}"
+    build:
+      context: .
+      target: "base"
+    command: "gradle --continuous runShadow"
+    volumes:
+      - "./:/home/gradle/galaxy-raiders/"
+    profiles:
+      - "dev"