add docker build

.github/workflows/docker.yml

@@ -0,0 +1,22 @@
+name: Publish to Registry
+on:
+  push:
+    branches:
+      - master
+    tags:
+      - v*
+jobs:
+  push:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Get release version
+      id: get_version
+      run: echo ::set-env name=RELEASE_VERSION::$(echo ${GITHUB_REF:10})
+    - name: Publish to Registry
+      uses: elgohr/Publish-Docker-Github-Action@master
+      with:
+        name: vadv/prometheus-exporter-merger
+        username: ${{ secrets.DOCKER_USERNAME }}
+        password: ${{ secrets.DOCKER_PASSWORD }}
+        tags: "latest,${{ env.RELEASE_VERSION }}"

Dockerfile

@@ -0,0 +1,20 @@
+FROM golang:1.14-alpine3.11 as builder
+
+RUN apk add --no-cache git make gcc libc-dev
+
+COPY go.mod .
+COPY go.sum .
+RUN go mod download
+
+COPY . .
+RUN go build --ldflags "-s -w -linkmode external -extldflags -static" --tags netcgo -o /prometheus-exporter-merger
+
+FROM scratch
+
+ENTRYPOINT ["/prometheus-exporter-merger"]
+USER nobody
+EXPOSE 8080
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+COPY --from=builder /etc/passwd /etc/passwd
+COPY --from=builder  /prometheus-exporter-merger /prometheus-exporter-merger
+ENTRYPOINT /prometheus-exporter-merger