dockerfile: Do a clean build in the dockerfile

When building a docker container, perform a clean build of the
component within the container instead of relying on the
go toolchain on the invoking machine and whatever the latest
(possibly stale) binary in the directory tree is.

Build dependency caching is enabled to reduce download times.

OCI container labels are added to provide standard container
metadata.

File locations, default invocation etc is the same as the
original 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"]