Health check endpoints in Node.js - Step-by-Step Execution

Concept Flow - Health check endpoints

Start Server

↓

Receive HTTP Request

↓

Check if URL is /health

↓

Run Health Check

↓

Return Status 200 and JSON

↓

End Request

The server listens for requests, checks if the URL is /health, runs a health check, and returns a status response.

Execution Sample

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.url === '/health') {
    res.writeHead(200, {'Content-Type': 'application/json'});
    res.end(JSON.stringify({status: 'ok'}));
  } else {
    res.writeHead(404);
    res.end();
  }
});

server.listen(3000);

This code creates a simple HTTP server that responds with a JSON status when /health is requested.

Execution Table

Step	Request URL	Condition (req.url === '/health')	Action	Response Status	Response Body
1	/health	true	Send 200 with JSON {status: 'ok'}	200	{"status":"ok"}
2	/other	false	Send 404 with empty body	404

💡 Requests not matching /health get 404; /health requests return 200 with status JSON.

Variable Tracker

Variable	Start	After Step 1	After Step 2
req.url	undefined	/health	/other
res.statusCode	undefined	200	404
res.body	undefined	{"status":"ok"}

Key Moments - 2 Insights

Why does the server return 404 for URLs other than /health?

Because the condition req.url === '/health' is false for other URLs, so the else branch sends a 404 response as shown in execution_table row 2.

What does the server send back when the URL is /health?

It sends a 200 status with a JSON body {"status":"ok"}, as shown in execution_table row 1.

Visual Quiz - 3 Questions

Look at the execution table, what is the response status when the request URL is '/health'?

A 500

B 404

C 200

D 301

💡 Hint

Check the Response Status column in execution_table row 1.

At which step does the condition req.url === '/health' evaluate to false?

A Step 2

B Step 1

C Both steps

D Never

💡 Hint

Look at the Condition column in execution_table row 2.

If the server code is changed to respond with status 503 on /health, how would the response status change in the table?

A It would stay 200

B It would change to 503

C It would become 404

D It would be empty

💡 Hint

Focus on the Action and Response Status columns for /health requests.

Concept Snapshot

Health check endpoints listen for a specific URL (e.g., /health).
If the request URL matches, respond with status 200 and a JSON status.
If not, respond with 404 or other error.
This helps external systems check if the server is running.
Use simple HTTP server code to implement.
Always return JSON for easy parsing.

Full Transcript

A health check endpoint is a special URL on a server that tells if the server is working. When the server gets a request, it checks if the URL is '/health'. If yes, it sends back a 200 status code and a JSON message {"status":"ok"}. If the URL is different, it sends a 404 status code. This lets other systems or users know if the server is alive and healthy. The example code uses Node.js's http module to create this simple server. The execution table shows two cases: one where the URL is '/health' and one where it is not. Variables like req.url and res.statusCode change accordingly. This pattern is common in web services to monitor uptime and readiness.