Add MetricsBackend with prometheus counter support

Dockerfile

@@ -21,15 +21,29 @@ WORKDIR /usr/src/minetest
 RUN apk add --no-cache git build-base irrlicht-dev cmake bzip2-dev libpng-dev \
 		jpeg-dev libxxf86vm-dev mesa-dev sqlite-dev libogg-dev \
 		libvorbis-dev openal-soft-dev curl-dev freetype-dev zlib-dev \
-		gmp-dev jsoncpp-dev postgresql-dev && \
+		gmp-dev jsoncpp-dev postgresql-dev ca-certificates && \
 	git clone --depth=1 -b ${MINETEST_GAME_VERSION} https://github.com/minetest/minetest_game.git ./games/minetest_game && \
-	rm -fr ./games/minetest_game/.git && \
-	mkdir build && \
+	rm -fr ./games/minetest_game/.git
+
+WORKDIR /usr/src/
+RUN git clone --recursive https://github.com/jupp0r/prometheus-cpp/ && \
+	mkdir prometheus-cpp/build && \
+	cd prometheus-cpp/build && \
+	cmake .. \
+		-DCMAKE_INSTALL_PREFIX=/usr/local \
+		-DCMAKE_BUILD_TYPE=Release \
+		-DENABLE_TESTING=0 && \
+	make -j2 && \
+	make install
+
+WORKDIR /usr/src/minetest
+RUN mkdir build && \
 	cd build && \
 	cmake .. \
 		-DCMAKE_INSTALL_PREFIX=/usr/local \
 		-DCMAKE_BUILD_TYPE=Release \
 		-DBUILD_SERVER=TRUE \
+		-DENABLE_PROMETHEUS=TRUE \
 		-DBUILD_UNITTESTS=FALSE \
 		-DBUILD_CLIENT=FALSE && \
 	make -j2 && \
@@ -49,6 +63,6 @@ COPY --from=0 /usr/local/share/doc/minetest/minetest.conf.example /etc/minetest/
 
 USER minetest:minetest
 
-EXPOSE 30000/udp
+EXPOSE 30000/udp 30000/tcp
 
 CMD ["/usr/local/bin/minetestserver", "--config", "/etc/minetest/minetest.conf"]