131 lines
4.8 KiB
Go
131 lines
4.8 KiB
Go
// Copyright 2014 Prometheus Team
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package prometheus_test
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import (
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"sync"
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"github.com/prometheus/client_golang/prometheus"
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)
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// ClusterManager is an example for a system that might have been built without
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// Prometheus in mind. It models a central manager of jobs running in a
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// cluster. To turn it into something that collects Prometheus metrics, we
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// simply add the two methods required for the Collector interface.
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//
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// An additional challenge is that multiple instances of the ClusterManager are
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// run within the same binary, each in charge of a different zone. We need to
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// make use of ConstLabels to be able to register each ClusterManager instance
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// with Prometheus.
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type ClusterManager struct {
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Zone string
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OOMCount *prometheus.CounterVec
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RAMUsage *prometheus.GaugeVec
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mtx sync.Mutex // Protects OOMCount and RAMUsage.
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// ... many more fields
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}
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// ReallyExpensiveAssessmentOfTheSystemState is a mock for the data gathering a
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// real cluster manager would have to do. Since it may actually be really
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// expensive, it must only be called once per collection. This implementation,
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// obviously, only returns some made-up data.
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func (c *ClusterManager) ReallyExpensiveAssessmentOfTheSystemState() (
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oomCountByHost map[string]int, ramUsageByHost map[string]float64,
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) {
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// Just example fake data.
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oomCountByHost = map[string]int{
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"foo.example.org": 42,
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"bar.example.org": 2001,
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}
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ramUsageByHost = map[string]float64{
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"foo.example.org": 6.023e23,
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"bar.example.org": 3.14,
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}
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return
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}
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// Describe faces the interesting challenge that the two metric vectors that are
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// used in this example are already Collectors themselves. However, thanks to
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// the use of channels, it is really easy to "chain" Collectors. Here we simply
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// call the Describe methods of the two metric vectors.
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func (c *ClusterManager) Describe(ch chan<- *prometheus.Desc) {
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c.OOMCount.Describe(ch)
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c.RAMUsage.Describe(ch)
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}
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// Collect first triggers the ReallyExpensiveAssessmentOfTheSystemState. Then it
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// sets the retrieved values in the two metric vectors and then sends all their
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// metrics to the channel (again using a chaining technique as in the Describe
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// method). Since Collect could be called multiple times concurrently, that part
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// is protected by a mutex.
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func (c *ClusterManager) Collect(ch chan<- prometheus.Metric) {
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oomCountByHost, ramUsageByHost := c.ReallyExpensiveAssessmentOfTheSystemState()
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c.mtx.Lock()
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defer c.mtx.Unlock()
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for host, oomCount := range oomCountByHost {
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c.OOMCount.WithLabelValues(host).Set(float64(oomCount))
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}
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for host, ramUsage := range ramUsageByHost {
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c.RAMUsage.WithLabelValues(host).Set(ramUsage)
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}
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c.OOMCount.Collect(ch)
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c.RAMUsage.Collect(ch)
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// All metrics in OOMCount and RAMUsage are sent to the channel now. We
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// can safely reset the two metric vectors now, so that we can start
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// fresh in the next Collect cycle. (Imagine a host disappears from the
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// cluster. If we did not reset here, its Metric would stay in the
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// metric vectors forever.)
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c.OOMCount.Reset()
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c.RAMUsage.Reset()
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}
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// NewClusterManager creates the two metric vectors OOMCount and RAMUsage. Note
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// that the zone is set as a ConstLabel. (It's different in each instance of the
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// ClusterManager, but constant over the lifetime of an instance.) The reported
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// values are partitioned by host, which is therefore a variable label.
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func NewClusterManager(zone string) *ClusterManager {
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return &ClusterManager{
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Zone: zone,
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OOMCount: prometheus.NewCounterVec(
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prometheus.CounterOpts{
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Subsystem: "clustermanager",
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Name: "oom_count",
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Help: "number of OOM crashes",
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ConstLabels: prometheus.Labels{"zone": zone},
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},
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[]string{"host"},
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),
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RAMUsage: prometheus.NewGaugeVec(
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prometheus.GaugeOpts{
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Subsystem: "clustermanager",
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Name: "ram_usage_bytes",
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Help: "RAM usage as reported to the cluster manager",
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ConstLabels: prometheus.Labels{"zone": zone},
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},
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[]string{"host"},
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),
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}
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}
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func ExampleCollector_clustermanager() {
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workerDB := NewClusterManager("db")
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workerCA := NewClusterManager("ca")
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prometheus.MustRegister(workerDB)
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prometheus.MustRegister(workerCA)
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// Since we are dealing with custom Collector implementations, it might
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// be a good idea to enable the collect checks in the registry.
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prometheus.EnableCollectChecks(true)
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}
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