Health check endpoints in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a basic health check endpoint using Express.

Node.js

const express = require('express');
const app = express();

app.get('/health', (req, res) => {
  res.status([1]).send('OK');
});

app.listen(3000);

Drag options to blanks, or click blank then click option'

A404

B200

C500

D302

Attempts:

3 left

💡 Hint

Common Mistakes

Using 404 or 500 status codes which indicate errors.

Forgetting to send a response.

The health check endpoint should respond with HTTP status 200 to indicate the service is healthy.

2fill in blank

medium

Complete the code to send a JSON response with status and uptime in the health check endpoint.

Node.js

app.get('/health', (req, res) => {
  res.status(200).json({
    status: 'ok',
    uptime: process.[1]()
  });
});

Drag options to blanks, or click blank then click option'

Auptime

BmemoryUsage

CcpuUsage

Denv

Attempts:

3 left

💡 Hint

Common Mistakes

Using memoryUsage or cpuUsage which return different info.

Trying to access a property instead of calling a method.

The process.uptime() method returns the number of seconds the current Node.js process has been running, useful for health checks.

3fill in blank

hard

Fix the error in the health check middleware to properly handle asynchronous checks.

Node.js

app.get('/health', async (req, res) => {
  const dbHealthy = await checkDatabaseConnection();
  if (!dbHealthy) {
    res.status([1]).json({ status: 'error' });
  } else {
    res.status(200).json({ status: 'ok' });
  }
});

Drag options to blanks, or click blank then click option'

A200

B500

C404

D503

Attempts:

3 left

💡 Hint

Common Mistakes

Using 200 status code even when the database is down.

Using 404 which means not found.

When a dependent service like a database is down, the health check should respond with HTTP 503 Service Unavailable.

4fill in blank

hard

Fill both blanks to create a reusable health check middleware that sends JSON status and sets correct HTTP status code.

Node.js

function healthCheckMiddleware(req, res) {
  const healthy = checkSystemHealth();
  res.status([1]).json({ status: [2] });
}

Drag options to blanks, or click blank then click option'

A200

B'ok'

D503

Attempts:

3 left

💡 Hint

Common Mistakes

Using numeric status code as string or vice versa.

Sending status code 503 when system is healthy.

The middleware should respond with status 200 and JSON status 'ok' when the system is healthy.

5fill in blank

hard

Fill all three blanks to create an advanced health check endpoint that checks database, cache, and returns appropriate status.

Node.js

app.get('/health', async (req, res) => {
  const dbOk = await checkDB();
  const cacheOk = await checkCache();
  if (dbOk && cacheOk) {
    res.status([1]).json({ status: [2] });
  } else {
    res.status([3]).json({ status: 'error' });
  }
});

Drag options to blanks, or click blank then click option'

A200

B'ok'

C503

D'healthy'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong status codes for failure.

Returning wrong status string for success.

When both database and cache are healthy, respond with 200 and status 'ok'. Otherwise, respond with 503 and status 'error'.

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