Add docker build

.github/workflows/docker.yml

@@ -0,0 +1,44 @@
+name: Docker Image CI
+
+on:
+  push:
+    branches: [master]
+    tags: ['v*']
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Login to DockerHub
+      uses: docker/login-action@v1
+      with:
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+
+    - name: Build the Docker image
+      run: docker build -t squid-exporter .
+
+    - name: Tag the Docker image latest
+      run: docker tag squid-exporter ${{ secrets.DOCKER_USERNAME }}/squid-exporter:latest
+
+    - name: Push the Docker image latest
+      uses: docker/build-push-action@v2
+      with:
+        context: .
+        push: true
+        tags: ${{ secrets.DOCKER_USERNAME }}/squid-exporter:latest
+
+    - name: Tag the Docker image version
+      if: startsWith(github.ref, 'refs/tags/v')
+      run: docker tag squid-exporter ${{ secrets.DOCKER_USERNAME }}/squid-exporter:${{ github.ref_name }}
+
+    - name: Push the Docker image latest
+      if: startsWith(github.ref, 'refs/tags/v')
+      uses: docker/build-push-action@v2
+      with:
+        context: .
+        push: true
+        tags: ${{ secrets.DOCKER_USERNAME }}/squid-exporter:${{ github.ref_name }}