Export OpenCensus metrics to Stackdriver

[knyar]

Currently OpenCensus metrics are only exposed to Prometheus for scraping. This adds a flag that also makes them reported to Stackdriver.

CC @jkohen who owns #8 this is probably related to.

[jkohen]

Thanks! Note that before we can close #8, we need to replace all Prometheus client metrics with OpenCensus. E.g.

stackdriver-prometheus-sidecar/stackdriver/queue_manager.go

Lines 48 to 111 in 79587ea

	succeededSamplesTotal = prometheus.NewCounterVec(
	prometheus.CounterOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "succeeded_samples_total",
	Help: "Total number of samples successfully sent to remote storage.",
	},
	[]string{queue},
	)
	failedSamplesTotal = prometheus.NewCounterVec(
	prometheus.CounterOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "failed_samples_total",
	Help: "Total number of samples which failed on send to remote storage.",
	},
	[]string{queue},
	)
	droppedSamplesTotal = prometheus.NewCounterVec(
	prometheus.CounterOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "dropped_samples_total",
	Help: "Total number of samples which were dropped due to the queue being full.",
	},
	[]string{queue},
	)
	sentBatchDuration = prometheus.NewHistogramVec(
	prometheus.HistogramOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "sent_batch_duration_seconds",
	Help: "Duration of sample batch send calls to the remote storage.",
	Buckets: prometheus.DefBuckets,
	},
	[]string{queue},
	)
	queueLength = prometheus.NewGaugeVec(
	prometheus.GaugeOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "queue_length",
	Help: "The number of processed samples queued to be sent to the remote storage.",
	},
	[]string{queue},
	)
	queueCapacity = prometheus.NewGaugeVec(
	prometheus.GaugeOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "queue_capacity",
	Help: "The capacity of the queue of samples to be sent to the remote storage.",
	},
	[]string{queue},
	)
	numShards = prometheus.NewGaugeVec(
	prometheus.GaugeOpts{
	Namespace: namespace,
	Subsystem: subsystem,
	Name: "shards",
	Help: "The number of shards used for parallel sending to the remote storage.",
	},
	[]string{queue},
	)

That means that this PR will only get you select metrics into Stackdriver. If this is an issue for you, we'd appreciate the feedback on issue #8. I think we should find the time to make the change now that OpenCensus supports gauges idiomatically.

[knyar]

That means that this PR will only get you select metrics into Stackdriver.

That's exactly what I'd like to achieve. I am working on another PR that will add a few OpenCensus metrics, so just wanted to make sure there's a way to get them reported to Stackdriver, not just Prometheus.

[jkohen]

I don't want to be too picky about this, but the flag name is unclear. I'd call it something like monitoring.backend and make the default value "prometheus" and have "stackdriver" as optional. WDYT?

[knyar]

Thanks, that's a good idea. Renamed to --monitoring.backend.