Add readiness check support and documentation

README.md

@@ -4,14 +4,42 @@
 
 A library for adding reform standard compliant healthchecks to nodejs applications.
 
+It exposes 3 endpoints:
+
+1. `/health` - Returns 200 by default  along with `buildInfo`, can optionally include result evaluating all `checks` passed in config.
+2. `/health/livness` - Returns 200 always.
+3. `/health/readiness` - Returns 200 by default , can optionally include result evaluating all `readinessChecks` passed in config.
+
 ## Usage
 
 Configure an express.js handler with checks.
 
 ```javascript
-const healthcheck = require('@hmcts/nodejs-healthcheck');
+const config = {
+  checks: {
+    mySimpleWebCheck: healthcheck.web("https://example.com/status"),
+    myComplexWebCheck: healthcheck.web("https://example.com/other", {
+      callback: (err, res) => {
+        return res.body.status == "good" ? healthcheck.up() : healthcheck.down()
+      },
+      timeout: 5000,
+      deadline: 10000,
+    }),
+    myRawCheck: healthcheck.raw(() => {
+      return myInternalCheck() ? healthcheck.up() : healthcheck.down()
+    })
+  },
+  buildInfo: {
+    myCustomBuildInfo: "yay"
+  }
+};
+healthcheck.addTo(app, config);
+```
 
-app.get("/status", healthcheck.configure({
+You can optionally include [readiness checks](#what-to-include-in-readiness-checks).
+
+```javascript
+const config = {
   checks: {
     mySimpleWebCheck: healthcheck.web("https://example.com/status"),
     myComplexWebCheck: healthcheck.web("https://example.com/other", {
@@ -25,12 +53,34 @@ app.get("/status", healthcheck.configure({
       return myInternalCheck() ? healthcheck.up() : healthcheck.down()
     })
   },
+  readinessChecks: {
+    mySimpleWebCheck: healthcheck.web("https://example.com/status")
+  },
   buildInfo: {
     myCustomBuildInfo: "yay"
   }
-}));
+};
+healthcheck.addTo(app, config);
 ```
 
+## what to include in readiness checks
+
+- On Kubernetes, readiness probes will be called periodically throughout the lifetime of the container. Container will be made temporarily unavailable from serving traffic when the readiness check fails.
+- The requests won't even reach your application to handle errors. So, it is very important to consider what checks should be included into readiness probe.
+- While adding all dependant services to readiness check can help in identifying any misconfiguration during startup, it could cause unwanted downtime for the application.
+- K8s introduced startUp Probes (Alpha in  1.16 ) to handle startup cases separately.
+
+Based on above, you should include a dependency into readiness checks only if they are exclusive/hard dependencies for your service. Unavailability of soft dependencies needs to be handled in code to give appropriate customer experience.
+
+Good example for check to be included in readiness:
+
+- A private cache / database like `Redis` or `Elastic Search` which are exclusive to the application (not shared).
+
+Bad example for check to be included in readiness:
+
+- Any shared components like IDAM, S2S or CCD.
+
+
 ## Publishing
 
 Bump the version (SemVer) and create a release in the GitHub UI, Travis CI will then build test and release to the npm registry.

healthcheck/install.js

@@ -6,6 +6,7 @@ const outputs = require('./outputs')
 function addTo (app, config) {
   app.get('/health', routes.configure(config))
   app.get('/health/liveness', (req, res) => res.json(outputs.status(outputs.UP)))
+  app.get('/health/readiness', routes.checkReadiness(config.readinessChecks))
 }
 
 module.exports = {

healthcheck/routes.js

@@ -54,7 +54,33 @@ function configure (config) {
   }
 }
 
+function checkReadiness (readinessChecks = {}) {
+  const check = new checks.CompositeCheck(readinessChecks)
+
+  return (req, res) => {
+    return Promise
+      .resolve(check.call(req, res))
+      .then((results) => {
+        const allOk = Object.values(results)
+          .every((result) => result.status === outputs.UP)
+        const output = Object.assign(
+          outputs.status(allOk),
+          results
+        )
+        const status = allOk ? 200 : 500
+        if (!allOk) {
+          const downHealthChecks = Object.values(results)
+            .filter((result) => result.status === outputs.DOWN)
+
+          logger.error('Health check failed, result for down endpoints: ', JSON.stringify(downHealthChecks))
+        }
+        res.status(status).json(output)
+      })
+  }
+}
+
 module.exports = {
   getBuildInfo: getBuildInfo,
-  configure: configure
+  configure: configure,
+  checkReadiness: checkReadiness
 }

test/unit/installTest.js

@@ -32,7 +32,7 @@ describe('Testing liveness', function () {
   })
 })
 
-describe('Testing Readiness for 200 OK', function () {
+describe('Testing health for 200 OK', function () {
   it('should return 200 OK', function (done) {
     request(app)
       .get('/health')
@@ -46,3 +46,18 @@ describe('Testing Readiness for 200 OK', function () {
       })
   })
 })
+
+describe('Testing readiness for 200 OK', function () {
+  it('should return 200 OK', function (done) {
+    request(app)
+      .get('/health/readiness')
+      .expect(200)
+      .end((err, res) => {
+        if (err) {
+          return done(err)
+        }
+        expect(res.body.status).to.be.equal('UP')
+        done()
+      })
+  })
+})

test/unit/routesTest.js

@@ -121,6 +121,43 @@ describe('Routes', () => {
       return route(req, res)
     })
 
+    it('should return 200 and UP if readiness check is undefined', () => {
+      const route = routes.checkReadiness()
+      const [req, res] = makeReqRes(200, {
+        status: 'UP'
+      })
+
+      return route(req, res)
+    })
+
+    it('should return 200 OK if all checks pass', () => {
+      const route = routes.checkReadiness({
+        check1: makeCheck(true),
+        check2: makeCheck(true)
+      })
+      const [req, res] = makeReqRes(200, {
+        status: outputs.UP,
+        check1: { status: 'UP' },
+        check2: { status: 'UP' }
+      })
+
+      return route(req, res)
+    })
+
+    it('should return 500 DOWN if any readiness checks fail', () => {
+      const route = routes.checkReadiness({
+        check1: makeCheck(false),
+        check2: makeCheck(true)
+      })
+      const [req, res] = makeReqRes(500, {
+        status: 'DOWN',
+        check1: { status: 'DOWN' },
+        check2: { status: 'UP' }
+      })
+
+      return route(req, res)
+    })
+
     it('should return the extra build info', () => {
       const route = routes.configure({
         checks: {