feat(healthcheck): expose state to health checks (#185)

Author: okv

README.md

@@ -30,7 +30,8 @@ function onShutdown () {
   console.log('cleanup finished, server is shutting down');
 }
 
-function healthCheck () {
+function healthCheck ({ state }) {
+  // `state.isShuttingDown` (boolean) shows whether the server is shutting down or not
   return Promise.resolve(
     // optionally include a resolve value to be included as
     // info in the health check response
@@ -50,7 +51,7 @@ const server = http.createServer((request, response) => {
 const options = {
   // health check options
   healthChecks: {
-    '/healthcheck': healthCheck,    // a function returning a promise indicating service health,
+    '/healthcheck': healthCheck,    // a function accepting a state and returning a promise indicating service health,
     verbatim: true, // [optional = false] use object returned from /healthcheck verbatim in response,
     __unsafeExposeStackTraces: true // [optional = false] return stack traces in error response if healthchecks throw errors
   },

lib/standalone-tests/terminus.onsignal.nofail.js

@@ -7,7 +7,7 @@ const SIGNAL = 'SIGINT'
 
 createTerminus(server, {
   healthChecks: {
-    '/health': () => Promise.resolve()
+    '/health': ({ state }) => Promise.resolve({ state })
   },
   sendFailuresDuringShutdown: false,
   signal: SIGNAL,

lib/terminus.js

@@ -85,7 +85,7 @@ function decorateWithHealthCheck (server, state, options) {
         }
         let info
         try {
-          info = await healthCheck()
+          info = await healthCheck({ state })
         } catch (error) {
           logger('healthcheck failed', error)
           return sendFailure(res, { error: error.causes, exposeStackTraces: healthChecks.__unsafeExposeStackTraces })

lib/terminus.spec.js

@@ -216,6 +216,54 @@ describe('Terminus', () => {
       expect(loggerRan).to.eql(true)
     })
 
+    it('exposes internal state (isShuttingDown: false) to health check', async () => {
+      let onHealthCheckRan = false
+      let exposedState
+
+      createTerminus(server, {
+        healthChecks: {
+          '/health': ({ state }) => {
+            onHealthCheckRan = true
+            exposedState = state
+            return Promise.resolve()
+          }
+        }
+      })
+      server.listen(8000)
+
+      const response = await fetch('http://localhost:8000/health')
+      expect(response.status).to.eql(200)
+      expect(response.headers.has('Content-Type')).to.eql(true)
+      expect(response.headers.get('Content-Type')).to.eql('application/json')
+      expect(onHealthCheckRan).to.eql(true)
+      expect(exposedState).to.eql({ isShuttingDown: false })
+    })
+
+    it('exposes internal state (isShuttingDown: true) when shutting down', (done) => {
+      let responseAssertionsComplete = false
+      let exposedState
+
+      // We're only truly finished when the response has been analyzed and the forked http process has exited,
+      // freeing up port 8000 for future tests
+      execFile('node', ['lib/standalone-tests/terminus.onsignal.nofail.js'], (error) => {
+        expect(error.signal).to.eql('SIGINT')
+        expect(responseAssertionsComplete).to.eql(true)
+        expect(exposedState).to.eql({ isShuttingDown: true })
+        done()
+      })
+
+      // let the process start up
+      setTimeout(() => {
+        fetch('http://localhost:8000/health')
+          .then(async (res) => {
+            expect(res.status).to.eql(200)
+            responseAssertionsComplete = true
+            const json = await res.json()
+            exposedState = json.info.state
+          })
+      }, 300)
+    })
+
     describe('includes error on reject', async () => {
       const errors = [
         new Error('test error 1'),