build: add manual docker multistep build (!114)

- Include two Dockerfiles in the repo: one for Goreleaser and one for manual builds
- Update the Goreleaser config to use it's own Dockerfile
- The Dockerfile for manual builds uses a two step process to build the exporter - this way the base system does not need Go installed

https://gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/-/merge_requests/114

.goreleaser.yml

@@ -23,6 +23,7 @@ dockers:
   extra_files:
   - health
   use: buildx
+  dockerfile: Dockerfile.goreleaser
   build_flag_templates:
   - "--pull"
   - "--platform=linux/amd64"
@@ -42,6 +43,7 @@ dockers:
   extra_files:
   - health
   use: buildx
+  dockerfile: Dockerfile.goreleaser
   build_flag_templates:
   - "--pull"
   - "--platform=linux/arm64"

Dockerfile

@@ -1,11 +1,26 @@
+FROM golang:1.20-buster AS build
+
+# Create build workspace folder
+WORKDIR /workspace
+ADD . /workspace
+
+# Install updates and build tools
+RUN apt update --yes && \
+    apt install --yes build-essential
+
+# Build the actual binary
+RUN make build
+
+# -- -- -- -- -- --
+
+# Set up image to run the tool
 FROM alpine
 
 # Create main app folder to run from
 WORKDIR /app
 
-# Copy compiled binary to release image
-# (must build the binary before running docker build)
-COPY fail2ban_exporter /app/fail2ban_exporter
+# Copy built binary from build image
+COPY --from=build /workspace/fail2ban_exporter /app
 
 # Setup a healthcheck
 COPY health /app/health

Dockerfile.goreleaser

@@ -0,0 +1,15 @@
+FROM alpine
+
+# Create main app folder to run from
+WORKDIR /app
+
+# Copy compiled binary to release image
+# (must build the binary before running docker build)
+COPY fail2ban_exporter /app/fail2ban_exporter
+
+# Setup a healthcheck
+COPY health /app/health
+RUN apk add curl
+HEALTHCHECK --interval=10s --timeout=4s --retries=3 CMD /app/health
+
+ENTRYPOINT ["/app/fail2ban_exporter"]

Makefile

@@ -51,5 +51,5 @@ build:
 
 # Build project docker container
 .PHONY: build/docker
-build/docker: build
+build/docker:
 	docker build -t fail2ban-prometheus-exporter .