Makefile: build promtail with CGO_ENABLED if GOHOSTOS=GOOS=linux (#809)

This commit modifies the Makefile to build promtail with CGO_ENABLED if
both GOHOSTOS and GOOS are set to linux.

To facilitate the Docker container utilizing the journal support,
the container for promtail had to be modified to be based on top of
debian. The sd-journal library depends on libsystemd.so being present
at runtime. As alpine currently does not have a package for systemd,
the easiest approach is to change the base image to debian:stretch-slim.
A future solution for providing an alpine-based build will be considered
in the future and discussion for the approach will be tracked in #838.

This commit also updates the Dockerfile to default to using the
latest loki-build-image. If a specific version is required, it should
be provided as a build arg to docker build.

Makefile

@@ -40,11 +40,14 @@ APP_GO_FILES := $(shell find . $(DONT_FIND) -name .y.go -prune -o -name .pb.go -
 
 # Build flags
 VPREFIX := github.com/grafana/loki/vendor/github.com/prometheus/common/version
-GO_FLAGS := -ldflags "-extldflags \"-static\" -s -w -X $(VPREFIX).Branch=$(GIT_BRANCH) -X $(VPREFIX).Version=$(IMAGE_TAG) -X $(VPREFIX).Revision=$(GIT_REVISION)" -tags netgo
+GO_LDFLAGS   := -s -w -X $(VPREFIX).Branch=$(GIT_BRANCH) -X $(VPREFIX).Version=$(IMAGE_TAG) -X $(VPREFIX).Revision=$(GIT_REVISION)
+GO_FLAGS     := -ldflags "-extldflags \"-static\" $(GO_LDFLAGS)" -tags netgo
+DYN_GO_FLAGS := -ldflags "$(GO_LDFLAGS)" -tags netgo
 # Per some websites I've seen to add `-gcflags "all=-N -l"`, the gcflags seem poorly if at all documented
 # the best I could dig up is -N disables optimizations and -l disables inlining which should make debugging match source better.
 # Also remove the -s and -w flags present in the normal build which strip the symbol table and the DWARF symbol table.
-DEBUG_GO_FLAGS := -gcflags "all=-N -l" -ldflags "-extldflags \"-static\" -X $(VPREFIX).Branch=$(GIT_BRANCH) -X $(VPREFIX).Version=$(IMAGE_TAG) -X $(VPREFIX).Revision=$(GIT_REVISION)" -tags netgo
+DEBUG_GO_FLAGS     := -gcflags "all=-N -l" -ldflags "-extldflags \"-static\" $(GO_LDFLAGS)" -tags netgo
+DYN_DEBUG_GO_FLAGS := -gcflags "all=-N -l" -ldflags "$(GO_LDFLAGS)" -tags netgo
 
 NETGO_CHECK = @strings $@ | grep cgo_stub\\\.go >/dev/null || { \
        rm $@; \
@@ -151,6 +154,19 @@ cmd/loki-canary/loki-canary: $(APP_GO_FILES) cmd/loki-canary/main.go
 # Promtail #
 ############
 
+PROMTAIL_CGO := 0
+PROMTAIL_GO_FLAGS := $(GO_FLAGS)
+PROMTAIL_DEBUG_GO_FLAGS := $(DEBUG_GO_FLAGS)
+
+# Validate GOHOSTOS=linux && GOOS=linux to use CGO.
+ifeq ($(shell go env GOHOSTOS),linux)
+ifeq ($(shell go env GOOS),linux)
+PROMTAIL_CGO = 1
+PROMTAIL_GO_FLAGS = $(DYN_GO_FLAGS)
+PROMTAIL_DEBUG_GO_FLAGS = $(DYN_DEBUG_GO_FLAGS)
+endif
+endif
+
 promtail: yacc cmd/promtail/promtail
 promtail-debug: yacc cmd/promtail/promtail-debug
 
@@ -163,11 +179,11 @@ $(PROMTAIL_GENERATED_FILE): $(PROMTAIL_UI_FILES)
 	GOOS=$(shell go env GOHOSTOS) go generate -x -v ./pkg/promtail/server/ui
 
 cmd/promtail/promtail: $(APP_GO_FILES) $(PROMTAIL_GENERATED_FILE) cmd/promtail/main.go
-	CGO_ENABLED=0 go build $(GO_FLAGS) -o $@ ./$(@D)
+	CGO_ENABLED=$(PROMTAIL_CGO) go build $(PROMTAIL_GO_FLAGS) -o $@ ./$(@D)
 	$(NETGO_CHECK)
 
 cmd/promtail/promtail-debug: $(APP_GO_FILES) pkg/promtail/server/ui/assets_vfsdata.go cmd/promtail/main.go
-	CGO_ENABLED=0 go build $(DEBUG_GO_FLAGS) -o $@ ./$(@D)
+	CGO_ENABLED=$(PROMTAIL_CGO) go build $(PROMTAIL_DEBUG_GO_FLAGS) -o $@ ./$(@D)
 	$(NETGO_CHECK)
 
 #############
@@ -248,14 +264,14 @@ ifeq ($(BUILD_IN_CONTAINER),true)
 		-v $(shell pwd):/go/src/github.com/grafana/loki \
 		$(IMAGE_PREFIX)/loki-build-image:$(BUILD_IMAGE_VERSION) $@;
 else
-	case "$@" in 	\
-  	vendor*)			\
-  		protoc -I ./vendor:./$(@D) --gogoslick_out=plugins=grpc:./vendor ./$(patsubst %.pb.go,%.proto,$@); \
-  		;;					\
-  	*)						\
-  		protoc -I ./vendor:./$(@D) --gogoslick_out=Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,plugins=grpc:./$(@D) ./$(patsubst %.pb.go,%.proto,$@); \
-  		;;					\
-  	esac
+	case "$@" in	\
+		vendor*)			\
+			protoc -I ./vendor:./$(@D) --gogoslick_out=plugins=grpc:./vendor ./$(patsubst %.pb.go,%.proto,$@); \
+			;;					\
+		*)						\
+			protoc -I ./vendor:./$(@D) --gogoslick_out=Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,plugins=grpc:./$(@D) ./$(patsubst %.pb.go,%.proto,$@); \
+			;;					\
+		esac
 endif
 
 

cmd/docker-driver/Dockerfile

@@ -1,4 +1,4 @@
-ARG BUILD_IMAGE=grafana/loki-build-image:0.2.1
+ARG BUILD_IMAGE=grafana/loki-build-image:latest
 # Directories in this file are referenced from the root of the project not this folder
 # This file is intented to be called from the root like so:
 # docker build -t grafana/loki -f cmd/loki/Dockerfile .

cmd/loki-canary/Dockerfile

@@ -1,4 +1,4 @@
-ARG BUILD_IMAGE=grafana/loki-build-image:0.2.1
+ARG BUILD_IMAGE=grafana/loki-build-image:latest
 # Directories in this file are referenced from the root of the project not this folder
 # This file is intented to be called from the root like so:
 # docker build -t grafana/promtail -f cmd/promtail/Dockerfile .

cmd/loki/Dockerfile

@@ -1,4 +1,4 @@
-ARG BUILD_IMAGE=grafana/loki-build-image:0.2.1
+ARG BUILD_IMAGE=grafana/loki-build-image:latest
 # Directories in this file are referenced from the root of the project not this folder
 # This file is intented to be called from the root like so:
 # docker build -t grafana/loki -f cmd/loki/Dockerfile .

cmd/promtail/Dockerfile

@@ -1,4 +1,4 @@
-ARG BUILD_IMAGE=grafana/loki-build-image:0.2.1
+ARG BUILD_IMAGE=grafana/loki-build-image:latest
 # Directories in this file are referenced from the root of the project not this folder
 # This file is intented to be called from the root like so:
 # docker build -t grafana/promtail -f cmd/promtail/Dockerfile .
@@ -12,10 +12,15 @@ COPY . /go/src/github.com/grafana/loki
 WORKDIR /go/src/github.com/grafana/loki
 RUN GOARCH=$(cat /goarch) GOARM=$(cat /goarm) make clean && make promtail
 
-FROM alpine:3.9
+# Promtail requires debian as the base image to support systemd journal reading
+FROM debian:stretch-slim
 # tzdata required for the timestamp stage to work
-RUN apk add --update --no-cache ca-certificates tzdata
+RUN apt-get update && \
+    apt-get install -qy \
+      tzdata ca-certificates libsystemd-dev && \
+    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 COPY --from=build /go/src/github.com/grafana/loki/cmd/promtail/promtail /usr/bin/promtail
 COPY cmd/promtail/promtail-local-config.yaml /etc/promtail/local-config.yaml
 COPY cmd/promtail/promtail-docker-config.yaml /etc/promtail/docker-config.yaml
 ENTRYPOINT ["/usr/bin/promtail"]
+