Prometheus metrics reporting

package.json

@@ -38,6 +38,7 @@
     "minimatch": "^3.0.4",
     "probot": "^7.4.0",
     "probot-config": "^1.0.1",
+    "prom-client": "^11.3.0",
     "raven": "^2.6.4"
   },
   "devDependencies": {

src/index.ts

@@ -4,15 +4,25 @@ import { WorkerContext } from './models'
 import Raven from 'raven'
 import { RepositoryWorkers } from './repository-workers'
 import sentryStream from 'bunyan-sentry-stream'
+import { Headers } from 'probot/lib/github'
 import { RepositoryReference, PullRequestReference } from './github-models'
 import myAppId from './myappid'
+import { metricsReporter } from './metrics'
 
 async function getWorkerContext (options: {app: Application, context: Context, installationId: number}): Promise<WorkerContext> {
   const { app, context, installationId } = options
   const config = await loadConfig(context)
   const log = app.log
   const createGitHubAPI = async () => {
-    return app.auth(installationId, log)
+    const github = await app.auth(installationId, log)
+    const { owner, repo } = options.context.repo()
+    github.hook.after('request', (response, requestOptions) => {
+      const responseHeaders = response.headers as Headers
+      const rateLimit = Number(responseHeaders['x-ratelimit-remaining'])
+      const apiVersion = requestOptions.query ? 'v4' : 'v3'
+      metricsReporter.rateLimitGauge.set({ owner, repo, apiVersion }, rateLimit)
+    })
+    return github
   }
   return {
     createGitHubAPI,
@@ -90,6 +100,14 @@ export = (app: Application) => {
     })
   }
 
+  // Get an express router to expose new HTTP endpoints
+  const router = app.route('/')
+
+  // Add a new route
+  router.get('/metrics', (req: any, res: any) => {
+    res.send(metricsReporter.outputMetrics())
+  })
+
   app.on([
     'pull_request.opened',
     'pull_request.edited',

src/metrics.ts

@@ -0,0 +1,44 @@
+import promClient, { Gauge, labelValues } from 'prom-client'
+
+const makeMockGauge = (name: String): Partial<Gauge> => ({
+  set: (labels: labelValues | number, value: number) => {} // tslint:disable-line:no-empty
+})
+
+class MetricsReporter {
+  public rateLimitGauge: Gauge
+  public queueSizeGauge: Gauge
+
+  constructor (public enabled: boolean) {
+    this.enabled = enabled
+
+    if (this.enabled) {
+      promClient.collectDefaultMetrics()
+
+      this.rateLimitGauge = new promClient.Gauge({
+        name: 'probot_auto_merge_github_rate_limit_remaining',
+        help:
+          'Github rate limit as reported by the `x-ratelimit-remaining` header',
+        labelNames: ['owner', 'repo', 'apiVersion']
+      })
+
+      this.queueSizeGauge = new promClient.Gauge({
+        name: 'probot_auto_merge_pr_queue_size',
+        help: 'Number of PRs in the Probot Auto Merge queue',
+        labelNames: ['owner', 'repo']
+      })
+    } else {
+      this.rateLimitGauge = makeMockGauge('rate limit') as Gauge
+      this.queueSizeGauge = makeMockGauge('queue size') as Gauge
+    }
+  }
+
+  outputMetrics (): string {
+    return this.enabled ? promClient.register.metrics() : 'nothing'
+  }
+}
+
+const metricsReporter = new MetricsReporter(
+  process.env.NODE_ENV === 'production'
+)
+
+export { metricsReporter }

src/repository-worker.ts

@@ -2,10 +2,12 @@ import { WaitQueue } from './WaitQueue'
 import { RepositoryReference, PullRequestReference } from './github-models'
 import { handlePullRequest, PullRequestContext } from './pull-request-handler'
 import { WorkerContext } from './models'
+import { metricsReporter } from './metrics'
 
 export class RepositoryWorker {
   private waitQueue: WaitQueue<number>
   private context: WorkerContext
+  public sendMetricsInterval?: NodeJS.Timeout
 
   constructor (
     public repository: RepositoryReference,
@@ -17,7 +19,24 @@ export class RepositoryWorker {
     this.waitQueue = new WaitQueue<number>(
       (pullRequestNumber: number) => `${pullRequestNumber}`,
       this.handlePullRequestNumber.bind(this),
-      onDrain
+      () => {
+        this.sendMetricsInterval && clearInterval(this.sendMetricsInterval)
+        this.sendQueueSizeMetrics()
+        onDrain()
+      }
+    )
+
+    metricsReporter.enabled &&
+      (this.sendMetricsInterval = setInterval(
+        this.sendQueueSizeMetrics.bind(this),
+        1000
+      ))
+  }
+
+  private sendQueueSizeMetrics (): void {
+    metricsReporter.queueSizeGauge.set(
+      { owner: this.repository.owner, repo: this.repository.repo },
+      this.waitQueue.getQueuedTasks().length
     )
   }
 

test/mock.ts

@@ -78,7 +78,15 @@ export function createPullRequestInfo (pullRequestInfo?: Partial<PullRequestInfo
 
 export function createGithubApi (options?: DeepPartial<GitHubAPI>): GitHubAPI {
   return {
-    ...options
+    ...options,
+    hook: {
+      before: (when: string, cb: () => void) => {
+        return
+      },
+      after: (when: string, cb: () => void) => {
+        return
+      }
+    }
   } as GitHubAPI
 }