@hmcts/nodejs-healthcheck

Nodejs Healthcheck

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/liveness - 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.

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);

You can optionally include readiness checks.

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()
    })
  },
  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.

To Test

Run yarn install (if packages not downloaded) and then run yarn test to run unit tests