chore: rewrite dockerfile

Rewrite the Dockerfile to be ready for fully automating releases using GoReleaser.

Dockerfile

@@ -1,23 +1,10 @@
-# Using golang:latest instead of alpine because of issues with sqlite3
-FROM golang:latest AS build
-
-# Create build folder to compile tool
-WORKDIR /build
-
-# Copy source files to build folder and link to the /go folder
-COPY . /build
-RUN ln -s /go/src/ /build/src
-
-# Compile the tool using a Make command
-RUN make build/docker
-
-
 FROM debian:buster-slim
 
 # Create main app folder to run from
 WORKDIR /app
 
 # Copy compiled binary to release image
-COPY --from=build /build/src/fail2ban_exporter /app/fail2ban_exporter
+# (must build the binary before running docker build)
+COPY fail2ban_exporter /app/fail2ban_exporter
 
 ENTRYPOINT ["/app/fail2ban_exporter"]

Makefile

@@ -1,3 +1,5 @@
+.PHONY: download test fmt check/dependencies check/fmt build build/docker
+
 download:
 	go mod download
 
@@ -24,3 +26,6 @@ build:
 	" \
 	-o fail2ban_exporter \
 	exporter.go
+
+build/docker: build
+	docker build -t fail2ban-prometheus-exporter .