Health check endpoints in Node.js

Introduction

Health check endpoints help you quickly see if your app is running well. They tell you if the server is alive and ready to handle requests.

You want to monitor if your web server is up and responding.

You need to check if your app is ready before sending traffic to it.

You want to automate alerts if your service goes down.

You use cloud services or load balancers that require a health check URL.

You want to debug if your app is stuck or crashed.

Syntax

Node.js

app.get('/health', (req, res) => {
  res.status(200).send('OK');
});

This example uses Express.js to create a simple GET endpoint at '/health'.

The endpoint returns a 200 status with a simple message to show the app is healthy.

Examples

Basic health check returning 'OK' with status 200.

Node.js

app.get('/health', (req, res) => {
  res.status(200).send('OK');
});

Health check returning JSON with status and uptime in seconds.

Node.js

app.get('/health', (req, res) => {
  const uptime = process.uptime();
  res.json({ status: 'ok', uptime: uptime });
});

Health check that returns 503 if a service like a database is down.

Node.js

app.get('/health', (req, res) => {
  // Here you could check database or other services
  const dbConnected = true;
  if (dbConnected) {
    res.status(200).send('Healthy');
  } else {
    res.status(503).send('Service Unavailable');
  }
});

Sample Program

This Node.js program uses Express to create a server with a health check endpoint at '/health'. When you visit this URL, it returns a JSON object showing the app status and how long it has been running.

Node.js

import express from 'express';

const app = express();
const port = 3000;

app.get('/health', (req, res) => {
  const uptime = process.uptime();
  res.json({ status: 'ok', uptime: uptime.toFixed(2) });
});

app.listen(port, () => {
  console.log(`Server running on http://localhost:${port}`);
});

Important Notes

Keep health check endpoints simple and fast to avoid slowing down your app.

Use status codes: 200 means healthy, 503 means service unavailable.

Consider checking important dependencies like databases or APIs in your health check.

Summary

Health check endpoints show if your app is alive and ready.

They usually return a simple message or JSON with status info.

Use them to help monitor and manage your app in real time.

Practice

1. What is the main purpose of a health check endpoint in a Node.js application?

easy

A. To confirm the app is running and responsive

B. To handle user login requests

C. To serve static files like images

D. To connect to the database

Solution

1. Step 1: Understand the role of health check endpoints

   Health check endpoints are designed to verify if the application is alive and can respond to requests.

2. Step 2: Differentiate from other endpoints

   Endpoints for login, static files, or database connections serve different purposes unrelated to health checks.

3. Final Answer:

   To confirm the app is running and responsive -> Option A

4. Quick Check:

   Health check = confirms app is alive [OK]

Hint: Health check endpoints confirm app status quickly [OK]

Common Mistakes:

• Confusing health check with user authentication
• Thinking health check serves static content
• Assuming health check manages database connections

2. Which of the following is the correct way to define a simple health check endpoint using Express in Node.js?

easy

A. app.listen('/health', () => console.log('OK'))

B. app.post('/health', (req, res) => res.send('OK'))

C. app.get('/health', (req, res) => res.send('OK'))

D. app.use('/health', (req, res) => res.send('OK'))

Solution

1. Step 1: Identify the HTTP method for health checks

   Health checks typically use GET requests to allow simple status queries.

2. Step 2: Check Express syntax for route definition

   Using app.get with a path and a callback sending a response is the correct pattern.

3. Final Answer:

   app.get('/health', (req, res) => res.send('OK')) -> Option C

4. Quick Check:

   GET route with res.send('OK') = correct syntax [OK]

Hint: Health checks use GET routes with res.send [OK]

Common Mistakes:

• Using POST instead of GET for health checks
• Using app.use which matches all methods
• Confusing app.listen with route handling

3. Given this Express code snippet, what will the response be when a client requests /health?

const express = require('express');
const app = express();
app.get('/health', (req, res) => {
  res.json({ status: 'ok', uptime: process.uptime() });
});
app.listen(3000);

medium

A. No response because the route is not defined

B. A plain text 'ok' message

C. An error because res.json is not a function

D. A JSON object with status 'ok' and uptime in seconds

Solution

1. Step 1: Analyze the route handler

   The route '/health' uses res.json to send a JSON object with keys 'status' and 'uptime'.

2. Step 2: Understand process.uptime()

   process.uptime() returns the number of seconds the Node.js process has been running, a number value.

3. Final Answer:

   A JSON object with status 'ok' and uptime in seconds -> Option D

4. Quick Check:

   res.json sends JSON = JSON object response [OK]

Hint: res.json sends JSON object, not plain text [OK]

Common Mistakes:

• Thinking res.json is undefined
• Expecting plain text instead of JSON
• Assuming route is missing or broken

4. Identify the error in this health check endpoint code and choose the fix:

const express = require('express');
const app = express();
app.get('/health', (req, res) => {
  res.sendStatus(200).send('OK');
});
app.listen(3000);

medium

A. Replace res.sendStatus(200).send('OK') with res.status(200).send('OK')

B. Change app.get to app.post

C. Remove res.send('OK') and keep only res.sendStatus(200)

D. Add next parameter and call next() after res.sendStatus

Solution

1. Step 1: Understand res.sendStatus behavior

   res.sendStatus(200) sends the status and ends the response, so chaining .send('OK') causes an error.

2. Step 2: Use correct method chaining

   res.status(200).send('OK') sets status and sends body correctly without ending response prematurely.

3. Final Answer:

   Replace res.sendStatus(200).send('OK') with res.status(200).send('OK') -> Option A

4. Quick Check:

   res.status().send() chains properly, res.sendStatus() ends response [OK]

Hint: Use res.status().send() to set status and send body [OK]

Common Mistakes:

• Chaining send after sendStatus causes error
• Changing HTTP method unnecessarily
• Calling next() after sending response

5. You want to create a health check endpoint that returns JSON with status as 'ok' only if the database connection is alive, otherwise status is 'error'. Which approach correctly implements this in Node.js with Express?

hard

A. app.get('/health', (req, res) => {
checkDbConnection().then(() => res.json({ status: 'ok' }));
});

B. app.get('/health', async (req, res) => {
const dbAlive = await checkDbConnection();
res.json({ status: dbAlive ? 'ok' : 'error' });
});

C. app.get('/health', (req, res) => {
const dbAlive = checkDbConnection();
res.json({ status: dbAlive ? 'ok' : 'error' });
});

D. app.get('/health', (req, res) => {
res.json({ status: 'ok' });
});

Solution

1. Step 1: Recognize async database check

   Checking database connection is asynchronous, so await or then() must be used to get result.

2. Step 2: Validate correct async usage

   app.get('/health', async (req, res) => { const dbAlive = await checkDbConnection(); res.json({ status: dbAlive ? 'ok' : 'error' }); }); uses async/await properly to wait for checkDbConnection result before sending JSON response.

3. Final Answer:

   Use async function with await to check DB and respond accordingly -> Option B

4. Quick Check:

   Async/await needed for async DB check [OK]

Hint: Use async/await to handle async DB checks in health endpoint [OK]

Common Mistakes:

• Calling async function without await or then
• Ignoring DB status and always returning 'ok'
• Not handling promise results properly