Add dockerfile (#267)

* Add dockerfile

* Update dockerfile and add docker image release workflow

* Add readme for docker usage

* Swap Docker Hub for Github Container Registry

.github/workflows/docker.yml

@@ -0,0 +1,47 @@
+name: Docker
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions:
+  contents: read
+  packages: write
+
+env:
+  DOCKER_REPO: ghcr.io/discourse/prometheus_exporter
+
+jobs:
+  build-and-publish:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - name: Set vars
+        id: vars
+        run: |
+          echo "version=${GITHUB_REF#refs/tags/v}" >> $GITHUB_OUTPUT
+
+      - uses: actions/checkout@v3
+      - uses: docker/setup-qemu-action@v2
+      - uses: docker/setup-buildx-action@v2
+
+      - name: Login to Github Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push images
+        uses: docker/build-push-action@v3
+        with:
+          context: .
+          push: true
+          platforms: linux/amd64,linux/arm64
+          build-args: |
+            GEM_VERSION=${{ steps.vars.outputs.version }}
+          tags: |
+            ${{ env.DOCKER_REPO }}:${{ steps.vars.outputs.version }}
+            ${{ env.DOCKER_REPO }}:latest

Dockerfile

@@ -0,0 +1,9 @@
+ARG RUBY_VERSION=3.1
+ARG GEM_VERSION=
+
+FROM ruby:${RUBY_VERSION}-slim
+
+RUN gem install --no-doc --version=${GEM_VERSION} prometheus_exporter
+
+EXPOSE 9394
+ENTRYPOINT ["prometheus_exporter", "-b", "ANY"]

README.md

@@ -32,6 +32,7 @@ To learn more see [Instrumenting Rails with Prometheus](https://samsaffron.com/a
 * [Transport concerns](#transport-concerns)
 * [JSON generation and parsing](#json-generation-and-parsing)
 * [Logging](#logging)
+* [Docker Usage](#docker-usage)
 * [Contributing](#contributing)
 * [License](#license)
 * [Code of Conduct](#code-of-conduct)
@@ -963,6 +964,28 @@ You can also pass a log level (default is [`Logger::WARN`](https://ruby-doc.org/
 PrometheusExporter::Client.new(log_level: Logger::DEBUG)
 ```
 
+## Docker Usage
+
+You can run `prometheus_exporter` project using an official Docker image:
+
+```bash
+docker pull discourse/prometheus_exporter:latest
+# or use specific version
+docker pull discourse/prometheus_exporter:x.x.x
+```
+
+The start the container:
+
+```bash
+docker run -p 9394:9394 discourse/prometheus_exporter
+```
+
+Additional flags could be included:
+
+```
+docker run -p 9394:9394 discourse/prometheus_exporter --verbose --prefix=myapp
+```
+
 ## Docker/Kubernetes Healthcheck
 
 A `/ping` endpoint which only returns `PONG` is available so you can run container healthchecks :