Add Stackdriver Profiler through Labkit

This updates the labkit library and adds minimal changes
to the `monitoring.Serve` initialization, given the profiler
can be initialized without requiring Prometheus.

Makefile

@@ -13,7 +13,7 @@ BUILD_TIME := $(shell date -u +%Y%m%d.%H%M%S)
 GOBUILD := go build -ldflags "-X main.Version=$(VERSION_STRING) -X main.BuildTime=$(BUILD_TIME)"
 EXE_ALL := gitlab-zip-cat gitlab-zip-metadata gitlab-workhorse
 INSTALL := install
-BUILD_TAGS := tracer_static tracer_static_jaeger
+BUILD_TAGS := tracer_static tracer_static_jaeger continuous_profiler_stackdriver
 
 MINIMUM_SUPPORTED_GO_VERSION := 1.11
 

README.md

@@ -251,9 +251,9 @@ It is OK if a feature is only covered by integration tests.
 
 ## Distributed Tracing
 
-Workhorse supports distributed tracing through [LabKit](https://gitlab.com/gitlab-org/labkit/) using [OpenTracing APIs](https://opentracing.io).
+Workhorse supports distributed tracing through [LabKit][] using [OpenTracing APIs](https://opentracing.io).
 
-By default, no tracing implementation is linked into the binary, but different OpenTracing providers can be linked in using [build tags](https://golang.org/pkg/go/build/#hdr-Build_Constraints)/[build constraints](https://golang.org/pkg/go/build/#hdr-Build_Constraints). This can be done by setting the `BUILD_TAGS` make variable.
+By default, no tracing implementation is linked into the binary, but different OpenTracing providers can be linked in using [build tags][build-tags]/[build constraints][build-tags]. This can be done by setting the `BUILD_TAGS` make variable.
 
 For more details of the supported providers, see LabKit, but as an example, for Jaeger tracing support, include the tags: `BUILD_TAGS="tracer_static tracer_static_jaeger"`.
 
@@ -269,8 +269,34 @@ For example:
 GITLAB_TRACING=opentracing://jaeger ./gitlab-workhorse
 ```
 
+## Continuous Profiling
+
+Workhorse supports continuous profiling through [LabKit][] using [Stackdriver Profiler](https://cloud.google.com/profiler).
+
+By default, the Stackdriver Profiler implementation is linked in the binary using [build tags][build-tags], though it's not
+required and can be skipped.
+
+For example:
+
+```shell
+make BUILD_TAGS=""
+```
+
+Once Workhorse is compiled with Continuous Profiling, the profiler configuration can be set via `GITLAB_CONTINUOUS_PROFILING`
+environment variable.
+
+For example:
+
+```shell
+GITLAB_CONTINUOUS_PROFILING="stackdriver?service=workhorse&service_version=1.0.1&project_id=test-123 ./gitlab-workhorse"
+```
+
+More information about see the [LabKit monitoring docs](https://gitlab.com/gitlab-org/labkit/-/blob/master/monitoring/doc.go).
+
 ## License
 
 This code is distributed under the MIT license, see the LICENSE file.
 
 [brief-history-blog]: https://about.gitlab.com/2016/04/12/a-brief-history-of-gitlab-workhorse/
+[LabKit]: https://gitlab.com/gitlab-org/labkit/
+[build-tags]: https://golang.org/pkg/go/build/#hdr-Build_Constraints

go.mod

@@ -10,7 +10,6 @@ require (
 	github.com/golang/gddo v0.0.0-20190419222130-af0f2af80721
 	github.com/golang/protobuf v1.3.2
 	github.com/gomodule/redigo v2.0.0+incompatible
-	github.com/google/go-cmp v0.3.1 // indirect
 	github.com/gorilla/websocket v1.4.0
 	github.com/grpc-ecosystem/go-grpc-middleware v1.0.0
 	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0
@@ -22,11 +21,11 @@ require (
 	github.com/sirupsen/logrus v1.3.0
 	github.com/stretchr/testify v1.4.0
 	gitlab.com/gitlab-org/gitaly v1.74.0
-	gitlab.com/gitlab-org/labkit v0.0.0-20190902063225-3253d7975ca7
-	golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3
-	golang.org/x/net v0.0.0-20190613194153-d28f0bde5980
+	gitlab.com/gitlab-org/labkit v0.0.0-20200227174525-4f8041c014c2
+	golang.org/x/lint v0.0.0-20191125180803-fdd1cda4f05f
+	golang.org/x/net v0.0.0-20200114155413-6afb5195e5aa
 	golang.org/x/sys v0.0.0-20200202164722-d101bd2416d5 // indirect
-	golang.org/x/tools v0.0.0-20190621195816-6e04913cbbac
+	golang.org/x/tools v0.0.0-20200117161641-43d50277825c
 	google.golang.org/grpc v1.24.0
-	honnef.co/go/tools v0.0.1-2019.2.2
+	honnef.co/go/tools v0.0.1-2019.2.3
 )

main.go

@@ -121,17 +121,18 @@ func main() {
 		}()
 	}
 
+	monitoringOpts := []monitoring.Option{monitoring.WithBuildInformation(Version, BuildTime)}
+
 	if *prometheusListenAddr != "" {
+		monitoringOpts = append(monitoringOpts, monitoring.WithListenerAddress(*prometheusListenAddr))
+	}
+
 	go func() {
-			err := monitoring.Serve(
-				monitoring.WithListenerAddress(*prometheusListenAddr),
-				monitoring.WithBuildInformation(Version, BuildTime),
-			)
+		err := monitoring.Serve(monitoringOpts...)
 		if err != nil {
-				log.WithError(err).Error("Failed to start prometheus listener")
+			log.WithError(err).Error("Failed to start monitoring")
 		}
 	}()
-	}
 
 	secret.SetPath(*secretPath)
 	cfg := config.Config{