dockerfile: Do a clean build in the dockerfile

.dockerignore

@@ -1,3 +1,6 @@
 *
-!pg_exporter
-!pg_exporter.yml
+!go.mod
+!go.sum
+!main.go
+!exporter
+!pg_exporter.yml

Dockerfile

@@ -1,7 +1,38 @@
+# syntax=docker/dockerfile:1
+FROM golang:1.22-alpine AS builder-env
+
+# Build a self-contained pg_exporter container with a clean environment and no
+# dependencies.
+#
+# build with
+#
+#   docker buildx build -f Dockerfile --tag pg_exporter .
+#
+
+WORKDIR /build
+
+COPY go.mod go.sum ./
+RUN \
+  --mount=type=cache,target=/go/pkg/mod \
+  --mount=type=cache,target=/root/.cache/go-build \
+  CGO_ENABLED=0 GOOS=linux go mod download
+
+COPY . /build
+RUN \
+  --mount=type=cache,target=/go/pkg/mod \
+  --mount=type=cache,target=/root/.cache/go-build \
+  CGO_ENABLED=0 GOOS=linux go build -a -o /pg_exporter .
+
 FROM scratch
-LABEL maintainer="Vonng <[email protected]>"
+LABEL org.opencontainers.image.authors="Vonng <[email protected]>, Craig Ringer <[email protected]>" \
+      org.opencontainers.image.url="https://github.com/Vonng/pg_exporter" \
+      org.opencontainers.image.source="https://github.com/Vonng/pg_exporter" \
+      org.opencontainers.image.licenses="Apache-2.0" \
+      org.opencontainers.image.title="pg_exporter" \
+      org.opencontainers.image.description="PostgreSQL metrics exporter for Prometheus"
 
-COPY pg_exporter /bin/pg_exporter
+WORKDIR /bin
+COPY --from=builder-env /pg_exporter /bin/pg_exporter
 COPY pg_exporter.yml /etc/pg_exporter.yml
-
-ENTRYPOINT ["/bin/pg_exporter"]
+EXPOSE 9630/tcp
+ENTRYPOINT ["/bin/pg_exporter"]