Health check endpoints in Flask - Step-by-Step Execution

Concept Flow - Health check endpoints

Start Flask App

↓

Receive HTTP GET /health

↓

Run health check function

↓

Check system status

↓

If OK

↓

If NOT OK

↓

Send HTTP response

↓

End request

The app listens for a GET request on /health, runs checks, then returns a status response.

Execution Sample

Flask

from flask import Flask, jsonify
app = Flask(__name__)

@app.route('/health')
def health_check():
    return jsonify({'status': 'ok'}), 200

Defines a simple health check endpoint that returns status 'ok' with HTTP 200.

Execution Table

Step	Action	Input	Check Result	Response Sent
1	App starts and listens	N/A	N/A	N/A
2	GET request received	/health	N/A	N/A
3	Run health_check function	N/A	System OK	N/A
4	Return JSON response	{"status": "ok"}	N/A	HTTP 200 with JSON
5	Request ends	N/A	N/A	Response delivered

💡 Request ends after sending HTTP 200 response with status 'ok'.

Variable Tracker

Variable	Start	After Request
app	Flask instance created	Listening for requests
health_check response	None	{"status": "ok"}, 200

Key Moments - 2 Insights

Why does the health check return a JSON response instead of plain text?

The execution_table row 4 shows the function returns jsonify({'status': 'ok'}), which formats the response as JSON for easy machine reading.

What happens if the system is not OK in the health check?

Though not shown in this simple example, row 3 explains the check result. If not OK, the function would return a 500 error instead of 200.

Visual Quiz - 3 Questions

Look at the execution table, what response is sent at step 4?

A HTTP 500 Internal Server Error

B HTTP 200 with JSON {'status': 'ok'}

C HTTP 404 Not Found

D No response sent

💡 Hint

Check the 'Response Sent' column in row 4 of the execution_table.

At which step does the app receive the GET request for /health?

A Step 2

B Step 1

C Step 3

D Step 5

💡 Hint

Look at the 'Action' and 'Input' columns in the execution_table.

If the health check function returned a 500 error, which step would change?

A Step 2 - GET request received

B Step 3 - Run health_check function

C Step 4 - Return JSON response

D Step 5 - Request ends

💡 Hint

Step 4 shows the response sent; changing status code affects this step.

Concept Snapshot

Health check endpoints in Flask:
- Use @app.route('/health') with GET method
- Define a function returning JSON status and HTTP code
- Return 200 OK if system is healthy
- Return 500 or error code if unhealthy
- Helps monitoring tools check app status easily

Full Transcript

This example shows how a Flask app creates a health check endpoint at /health. When a GET request arrives, the app runs a function that returns a JSON response with status 'ok' and HTTP 200. This lets monitoring systems know the app is running fine. The execution table traces each step from app start, request received, function run, response sent, to request end. Variables like the Flask app instance and response data change accordingly. Key moments clarify why JSON is used and what happens if the system is not OK. The quiz tests understanding of the response sent, request step, and how errors affect the flow.