build: compile tool during docker build

Update the project Dockerfile to compile the tool during the docker build
instead of assuming the goreleaser tool was run previously. This allows
for custom data to be set in the compiled tool (e.g. compiled by docker)
and removes the dependency on another build step.
Update the Makefile to include a new command to build the tool for docker
which sets the version data correctly. Rename the docker commands to follow
the `docker/build-...` format to avoid confusion with the build commands.

Dockerfile

@@ -1,10 +1,24 @@
 # Using golang:latest instead of alpine because of issues with sqlite3
 FROM golang:latest
 
+# 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
+
+# Create main app folder to run from
 WORKDIR /app
-COPY dist/fail2ban-prometheus-exporter_linux_amd64/fail2ban-prometheus-exporter /app
-COPY docker/run.sh /app
 
+# Move compiled binary to app folder and delete build folder
+RUN mv /build/src/exporter /app/fail2ban-prometheus-exporter
+RUN rm -rf /build
+
+# Copy init script into main app folder and set as entry point
+COPY docker/run.sh /app/
 RUN chmod +x /app/*
-
 ENTRYPOINT /app/run.sh

Makefile

@@ -24,7 +24,11 @@ build/release:
 	./tools/goreleaser_linux_amd64 --rm-dist --skip-publish
 
 build/docker:
+	cd src/ && go build -o exporter \
+     -ldflags '-X main.version=$(shell git describe --tags) -X main.commit=${shell git rev-parse HEAD} -X "main.date=${shell date --rfc-3339=seconds}" -X main.builtBy=docker' exporter.go
+
+docker/build-latest:
 	docker build -t registry.gitlab.com/hectorjsmith/fail2ban-prometheus-exporter:latest .
 
-build/docker-tag:
+docker/build-tag:
 	docker build -t registry.gitlab.com/hectorjsmith/fail2ban-prometheus-exporter:$(shell git describe --tags) .