exporter.md

Write a new Collector for NDM Exporter

To write a new collector certain steps have to be followed.

1. Create a new file in ndm-exporter/collector/my-collector.go. This file will include the struct which will implement prometheus collector interface.

   type MyMetricCollector struct {
   	Client kubernetes.Client
   
   	sync.Mutex
   	requestInProgress bool
   
   	metrics *seachestmetrics.Metrics
   }
   

   The fields are

   • Client : used to interface with the database from which blockdevice information can be obtained
   • sync.Mutex and requestInProgress : to acquire lock on the collector so that at a time only a single request is being handled
   • metrics : The actual prometheus metrics fields. This struct will have the metrics that are exposed.

2. A Collect() and Describe() method need to be implemented for this struct. The Describe() will list out all the metrics, and Collect() will have the logic to fetch the metrics. All metrics fetched will be first converted into a BlockDevice struct, which is used to represent a blockdevice in NDM.

3. Create a new package for your new metrics and add one file. pkg/metrics/mymetrics/metrics.go. This fill will contain the struct for your metrics.

   type MetricsData struct {
   	mymetric1 *prometheus.GaugeVec
   	mymetric2 *prometheus.GaugeVec
   
   	rejectRequestCount prometheus.Counter
   	errorRequestCount  prometheus.Counter
   }
   
   type MetricsLabels struct {
   	Label1     string
   	Label2     string
   }
   
   type Metrics struct {
   	CollectorType string
   	MetricsData
   	MetricsLabels
   }
   

   • mymetric1 and mymetric2 are the metrics that will be exposed along with the rejected requests count and errored request count. Requests are rejected if a request is already in progress. Request errors when an error occurs during the collection of metrics
   • Labels are the metrics labels that are available with the metric. Each metric will have associated labels to identify the blockdevice for which the metric is exposed. CollectorType is the collector used to collect the metrics. Same metrics can be exposed by multiple collectors. They are identified by the namespace field in prometheus metrics.
   • Metrics struct should have builder methods WithMetric1, WithMetric2 to declare the prometheus metrics fields. SetMetric1, SetMetric2 methods will be used to the values to the metric.
   • MetricsLabels struct should have builder methods WithLabel1, WithLabel2 to set the label on the metric.

4. Once your new collector is implemented, it should be registered with the exporter. NDM has 2 types of exporter, one running at cluster level and other at node level. register your collector with the exporter, depending on where you need the collector to be run. prometheus.MustRegister(myCollector1, myCollector2)