Add mechanism to expire old prometheus metrics

Adds a wrapper around the prometheus client, which keeps track of the
last time a metrics was accessed, and removes old ones once they have
not been accessed for a period of time.

libraries/metrics/metrics.coffee

@@ -3,30 +3,25 @@ if process.env["USE_PROM_METRICS"] != "true"
 else
  	console.log("using prometheus")
 
-
-prom = require('prom-client')
-Register = require('prom-client').register
+prom = require('./prom_wrapper')
 
 collectDefaultMetrics = prom.collectDefaultMetrics
 
 appname = "unknown"
 hostname = require('os').hostname()
 
-buildKey = (key)-> "#{name}.#{hostname}.#{key}"
-buildGlobalKey = (key)-> "#{name}.global.#{key}"
-
-promMetrics = {}
-
 destructors = []
 
 require "./uv_threadpool_size"
 
 module.exports = Metrics =
-	register:Register
-	initialize: (_name) ->
+	register: prom.registry
+
+	initialize: (_name, opts = {}) ->
 		appname = _name
 		collectDefaultMetrics({ timeout: 5000, prefix: Metrics.buildPromKey()})
-
+		if opts.ttlInMinutes
+			prom.ttlInMinutes = opts.ttlInMinutes
 
 		console.log("ENABLE_TRACE_AGENT set to #{process.env['ENABLE_TRACE_AGENT']}")
 		if process.env['ENABLE_TRACE_AGENT'] == "true"
@@ -67,8 +62,8 @@ module.exports = Metrics =
 
 	injectMetricsRoute: (app) ->
 		app.get('/metrics', (req, res) -> 
-			res.set('Content-Type', Register.contentType)
-			res.end(Register.metrics())
+			res.set('Content-Type', prom.registry.contentType)
+			res.end(prom.registry.metrics())
 		)
 
 	buildPromKey: (key = "")->
@@ -82,43 +77,23 @@ module.exports = Metrics =
 
 	inc : (key, sampleRate = 1, opts = {})->
 		key = Metrics.buildPromKey(key)
-		if !promMetrics[key]?
-			promMetrics[key] = new prom.Counter({
-				name: key,
-				help: key, 
-				labelNames: ['app','host','status','method', 'path']
-			})
 		opts.app = appname
 		opts.host = hostname
-		promMetrics[key].inc(opts)
+		prom.metric('counter', key).inc(opts)
 		if process.env['DEBUG_METRICS']
 			console.log("doing inc", key, opts)
 
 	count : (key, count, sampleRate = 1)->
 		key = Metrics.buildPromKey(key)
-		if !promMetrics[key]?
-			promMetrics[key] = new prom.Counter({
-				name: key,
-				help: key, 
-				labelNames: ['app','host']
-			})
-		promMetrics[key].inc({app: appname, host: hostname}, count)
+		prom.metric('counter', key).inc({app: appname, host: hostname}, count)
 		if process.env['DEBUG_METRICS']
 			console.log("doing count/inc", key, opts)
 
 	timing: (key, timeSpan, sampleRate, opts = {})->
 		key = Metrics.buildPromKey("timer_" + key)
-		if !promMetrics[key]?
-			promMetrics[key] = new prom.Summary({
-				name: key,
-				help: key,
-				maxAgeSeconds: 600,
-				ageBuckets: 10,
-				labelNames: ['app', 'host', 'path', 'status_code', 'method', 'collection', 'query']
-			})
 		opts.app = appname
 		opts.host = hostname
-		promMetrics[key].observe(opts, timeSpan)
+		prom.metric('summary', key).observe(opts, timeSpan)
 		if process.env['DEBUG_METRICS']
 			console.log("doing timing", key, opts)
 
@@ -137,25 +112,13 @@ module.exports = Metrics =
 
 	gauge : (key, value, sampleRate = 1, opts)->
 		key = Metrics.buildPromKey(key)
-		if !promMetrics[key]?
-			promMetrics[key] = new prom.Gauge({
-				name: key,
-				help: key, 
-				labelNames: ['app','host', 'status']
-			})
-		promMetrics[key].set({app: appname, host: hostname, status: opts?.status}, this.sanitizeValue(value))
+		prom.metric('gague', key).set({app: appname, host: hostname, status: opts?.status}, this.sanitizeValue(value))
 		if process.env['DEBUG_METRICS']
 			console.log("doing gauge", key, opts)
 			
 	globalGauge: (key, value, sampleRate = 1, opts)->
 		key = Metrics.buildPromKey(key)
-		if !promMetrics[key]?
-			promMetrics[key] = new prom.Gauge({
-				name: key,
-				help: key, 
-				labelNames: ['app','host', 'status']
-			})
-		promMetrics[key].set({app: appname, status: opts?.status},this.sanitizeValue(value))
+		prom.metric('gague', key).set({app: appname, status: opts?.status},this.sanitizeValue(value))
 
 	mongodb: require "./mongodb"
 	http: require "./http"

libraries/metrics/package.json

@@ -1,6 +1,6 @@
 {
   "name": "metrics-sharelatex",
-  "version": "2.2.0",
+  "version": "2.3.0",
   "description": "A drop-in metrics and monitoring module for node.js apps",
   "repository": {
     "type": "git",

libraries/metrics/prom_wrapper.coffee

@@ -0,0 +1,114 @@
+prom = require('prom-client')
+registry = require('prom-client').register
+metrics = {}
+
+
+optsKey = (opts) ->
+	keys = Object.keys(opts)
+	return '' if keys.length == 0
+
+	keys = keys.sort()
+
+	hash = '';
+	for key in keys
+		hash += "," if hash.length
+		hash += "#{key}:#{opts[key]}"
+
+	return hash
+
+extendOpts = (opts, labelNames) ->
+	for label in labelNames
+		opts[label] ||= ''
+	return opts
+
+optsAsArgs = (opts, labelNames) ->
+	args = []
+	for label in labelNames
+		args.push(opts[label] || '')
+	return args
+
+
+PromWrapper =
+	ttlInMinutes: 0
+	registry: registry
+
+	metric: (type, name) ->
+		registry.getSingleMetric(name) || new MetricWrapper(type, name)
+
+	collectDefaultMetrics: prom.collectDefaultMetrics
+
+
+class MetricWrapper
+	constructor: (type, name) ->
+		metrics[name] = this
+		@name = name
+		@instances = {}
+		@lastAccess = new Date()
+		@metric = switch type
+			when "counter"
+				new prom.Counter({
+					name: name,
+					help: name,
+					labelNames: ['app','host','status','method', 'path']
+				})
+			when "summary"
+				new prom.Summary({
+					name: name,
+					help: name,
+					maxAgeSeconds: 600,
+					ageBuckets: 10,
+					labelNames: ['app', 'host', 'path', 'status_code', 'method', 'collection', 'query']
+				})
+			when "gauge"
+				prom.Gauge({
+					name: name,
+					help: name,
+					labelNames: ['app','host', 'status']
+				})
+
+	inc: (opts, value) ->
+		@_execMethod 'inc', opts, value
+
+	observe: (opts, value) ->
+		@_execMethod 'observe', opts, value
+
+	set: (opts, value) ->
+		@_execMethod 'set', opts, value
+
+	sweep: () ->
+		thresh = new Date(Date.now() - 1000 * 60 * PromWrapper.ttlInMinutes)
+		for key in Object.keys(@instances)
+			if thresh > @instances[key].time
+				if process.env['DEBUG_METRICS']
+					console.log("Sweeping stale metric instance", @name, opts: @instances[key].opts, key)
+				@metric.remove(optsAsArgs(@instances[key].opts, @metric.labelNames)...)
+
+		if thresh > @lastAccess
+			if process.env['DEBUG_METRICS']
+				console.log("Sweeping stale metric", @name)
+			delete metrics[@name]
+			registry.removeSingleMetric(@name)
+
+	_execMethod: (method, opts, value) ->
+		opts = extendOpts(opts, @metric.labelNames)
+		key = optsKey(opts)
+		@instances[key] = { time: new Date(), opts } unless key == ''
+		@lastAccess = new Date()
+		@metric[method](opts, value)
+
+
+unless PromWrapper.sweepRegistered
+	if process.env['DEBUG_METRICS']
+		console.log("Registering sweep method")
+	PromWrapper.sweepRegistered = true
+	setInterval(
+		() ->
+			if PromWrapper.ttlInMinutes
+				if process.env['DEBUG_METRICS']
+					console.log("Sweeping metrics")
+				for key in Object.keys(metrics)
+					metrics[key].sweep()
+	60000)
+
+
+module.exports = PromWrapper