Health-check middleware for Moleculer

The following originally comes from a gist available here: https://gist.github.com/icebob/c717ae22002b9ecaa4b253a67952da3a

Most credits go to @icebob. This repository only provides us a way to publish, maintain and perhaps customize this middleware.

This module is available on the public NPM registry:

npm install @r2d2bzh/moleculer-healthcheck-middleware

Use it for Kubernetes liveness & readiness checks. The middleware opens a HTTP server on port 3001. To check, open the http://localhost:3001/live & http://localhost:3001/ready URLs.

Response

{
  "state": "up",
  "uptime": 7.419,
  "timestamp": 1562790370161
}

The state can be "starting" (503), "up" (200), "stopping" (503) or "down" (503).

Usage

Load with default options

// moleculer.config.js
const HealthMiddleware = require('@r2d2bzh/moleculer-healthcheck-middleware');

module.exports = {
  middlewares: [
    HealthMiddleware()
  ]
};

Load with custom options

// moleculer.config.js
const HealthMiddleware = require('@r2d2bzh/moleculer-healthcheck-middleware');

module.exports = {
  middlewares: [
    HealthMiddleware({
      port: 3333,
      readiness: {
        path: "/ready"
      },
      liveness: {
        path: "/live"
      }
    })
  ]
};

In order to check liveness and/or readiness a little deeper, you can also give the module your own checker function which takes a callback. If you give a parameter to the next callback you will tell the middlware to fail the liveness and/or readiness check. Also if you do not respond in a certain amount of time, the liveness and/or readiness check will fail.

// moleculer.config.js
const HealthMiddleware = require('@r2d2bzh/moleculer-healthcheck-middleware');

module.exports = {
  middlewares: [
    HealthMiddleware({
      liveness: {
        checkerTimeoutMs: 20000, // default value
        checker: function(next) {
          // Execute here your liveness check...
          if (ok) {
            next();
          } else {
            next('error');
          }
        },
      },
    }),
  ],
};

The checker can also be initialized through a createChecker factory which takes the broker as a parameter. Provide your own implementation of createChecker to the healthcheck middleware if you need the checker function to have access to the broker. It will be called during the started Moleculer middleware hook.

const HealthMiddleware = require('@r2d2bzh/moleculer-healthcheck-middleware');

module.exports = {
  middlewares: [
    HealthMiddleware({
      liveness: {
        createChecker: (broker) =>
          (next) => {
            if (ok) {
              broker.getLogger('healthcheck').info('Everything is fine.');
              next();
            } else {
              broker.getLogger('healthcheck').error('error');
              next('error');
            }
          }
        }
    }),
  ],
};

Usage in Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: greeter
spec:
  selector:
    matchLabels:
      app: greeter
  replicas: 1
  template:
    metadata:
      labels:
        app: greeter
    spec:
      containers:
      - name: greeter
        image: moleculer/demo:1.4.2
        livenessProbe:
          httpGet:
            path: /live
            port: 3001
        readinessProbe:
          httpGet:
            path: /ready
            port: 3001