feat: add last_state metric (external-secrets#357)

It is a bit difficult to alert on sync_calls since they trigger into an error state and may stay there.
This adds the gauge last_state.  With last_state, people can easily alert on a value < 0 to indicate failure.

README.md

@@ -435,6 +435,7 @@ kubernetes-external-secrets exposes the following metrics over a prometheus endp
 | Metric | Description | Example |
 | ----------------------------------------- | ------------------------------------------------------------------------------- | ----------------------------------------------------------------------------- |
 | `sync_calls` | This metric counts the number of sync calls by backend, secret name and status | `sync_calls{name="foo",namespace="example",backend="foo",status="success"} 1` |
+| `last_state` | A value of -1 or 1 where -1 means the last sync_call was an error and 1 means the last sync_call was a success | `last_state{name="foo",namespace="example",backend="foo"} 1` |
 
 
 ## Development

lib/metrics-server.test.js

@@ -57,5 +57,7 @@ describe('MetricsServer', () => {
 
  expect(res.text).to.have.string('sync_calls{name="foo",namespace="example",backend="foo",status="success"} 1')
  expect(res.text).to.have.string('sync_calls{name="bar",namespace="example",backend="foo",status="failed"} 1')
+ expect(res.text).to.have.string('last_state{name="foo",namespace="example",backend="foo"} 1')
+ expect(res.text).to.have.string('last_state{name="bar",namespace="example",backend="foo"} -1')
  })
 })

lib/metrics.js

@@ -15,6 +15,12 @@ class Metrics {
  labelNames: ['name', 'namespace', 'backend', 'status'],
  registers: [registry]
  })
+ this._lastState = new Prometheus.Gauge({
+ name: 'last_state',
+ help: 'Value -1 if the last sync was a failure, 1 otherwise.',
+ labelNames: ['name', 'namespace', 'backend'],
+ registers: [registry]
+ })
  }
 
  /**
@@ -31,6 +37,19 @@ class Metrics {
  backend,
  status
  })
+ if (status === 'success') {
+ this._lastState.set({
+ name,
+ namespace,
+ backend
+ }, 1)
+ } else {
+ this._lastState.set({
+ name,
+ namespace,
+ backend
+ }, -1)
+ }
  }
 }