Health check endpoints in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this FastAPI health check endpoint?

Consider this FastAPI endpoint code for a health check. What will the client receive when accessing /health?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/health")
async def health_check():
    return {"status": "ok", "uptime": 12345}

A "status: ok, uptime: 12345"

B {"status": "ok", "uptime": 12345}

C HTTP 404 Not Found error

D An empty JSON object {}

💡 Hint

Look at the return statement inside the endpoint function.

The endpoint returns a dictionary with keys status and uptime. FastAPI automatically converts this dictionary to JSON in the response.

📝 Syntax

intermediate

Which option correctly defines a FastAPI health check endpoint?

Select the code snippet that correctly defines a GET endpoint at /health returning JSON {"status": "healthy"}.

A

@app.get("/health")
async def health():
    return {"status": "healthy"}

B

app.get("/health")
async def health():
    return {"status": "healthy"}

C

@app.get("/health")
def health():
    print({"status": "healthy"})

D

@app.get("/health")
async def health():
    return "status: healthy"

💡 Hint

Remember the decorator syntax and that the function must return a dictionary for JSON.

Option A uses the correct decorator @app.get("/health") and returns a dictionary, which FastAPI converts to JSON.

Option A misses the decorator symbol '@'. Option A returns None and prints instead of returning. Option A returns a string, not JSON.

❓ state_output

advanced

What is the response status code of this health check endpoint?

Given this FastAPI health check endpoint, what HTTP status code will the client receive?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/health")
async def health_check():
    return {"status": "ok"}

A 500

B 404

C 200

D 302

💡 Hint

FastAPI returns 200 OK by default for successful GET requests.

When a FastAPI endpoint returns a dictionary without specifying a status code, the default HTTP status code is 200 (OK).

🔧 Debug

advanced

Why does this health check endpoint cause a runtime error?

Examine this FastAPI endpoint code. Why will it cause an error when accessed?

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/health")
async def health_check():
    return status: "ok"

A SyntaxError due to invalid return statement syntax

B TypeError because 'status' is undefined

C RuntimeError because async function is missing await

D No error, returns JSON {"status": "ok"}

💡 Hint

Look carefully at the return statement syntax.

The return statement uses invalid syntax. It should return a dictionary like {"status": "ok"}, but instead it uses a colon without braces, causing a SyntaxError.

🧠 Conceptual

expert

Which option best describes the purpose of a health check endpoint in FastAPI?

Choose the most accurate description of why a health check endpoint is used in FastAPI applications.

A To log detailed error messages when the app crashes

B To authenticate users before they access the main application features

C To serve the main homepage content of the application

D To provide a simple URL that external systems can call to verify the app is running and responsive

💡 Hint

Think about monitoring and uptime checks.

A health check endpoint is a simple URL that monitoring tools or load balancers call to confirm the app is alive and working. It does not handle authentication or serve main content.

Practice

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

easy

A. To serve static files like images

B. To handle user authentication

C. To confirm the app is running and responsive

D. To perform database migrations

Solution

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

   Health check endpoints are simple URLs that tell if the app is alive and working properly.

2. Step 2: Identify the correct purpose

   They do not handle authentication, serve files, or migrate databases but confirm app responsiveness.

3. Final Answer:

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

4. Quick Check:

   Health check = Confirm app alive [OK]

Hint: Health check endpoints confirm app is alive and responsive [OK]

Common Mistakes:

• Confusing health check with authentication endpoints
• Thinking health check serves files
• Assuming health check runs database tasks

2. Which of the following is the correct way to define a simple health check endpoint in FastAPI?

easy

A. @app.get('/health')
def health():
return {'status': 'ok'}

B. app.route('/health', method='GET')(def health(): return 'ok')

C. app.get('/health')(def health(): return {'status': 'ok'})

D. def health():
return {'status': 'ok'}
app.get('/health', health)

Solution

1. Step 1: Recall FastAPI syntax for endpoints

   FastAPI uses decorators like @app.get('/path') above the function to define GET endpoints.

2. Step 2: Check each option's syntax

   @app.get('/health') def health(): return {'status': 'ok'} correctly uses @app.get decorator and defines a function returning JSON. Others have syntax errors or wrong decorator usage.

3. Final Answer:

   @app.get('/health')\ndef health():\n return {'status': 'ok'} -> Option A

4. Quick Check:

   Use @app.get decorator for GET endpoints [OK]

Hint: Use @app.get decorator above function for GET endpoints [OK]

Common Mistakes:

• Using app.get() as a function call instead of decorator
• Wrong decorator syntax or missing @
• Returning string instead of JSON/dict

3. Given this FastAPI health check endpoint code, what will be the JSON response when accessed?

@app.get('/health')
def health():
    return {'status': 'healthy', 'uptime': 12345}

medium

A. 500 Internal Server Error

B. {"status": "ok"}

C. 404 Not Found

D. {"status": "healthy", "uptime": 12345}

Solution

1. Step 1: Analyze the return value of the endpoint

   The function returns a dictionary with keys 'status' and 'uptime' and their values.

2. Step 2: Understand FastAPI response conversion

   FastAPI converts dict returns to JSON automatically, so the response will be JSON with those keys and values.

3. Final Answer:

   {"status": "healthy", "uptime": 12345} -> Option D

4. Quick Check:

   Dict return becomes JSON response [OK]

Hint: Returned dict becomes JSON response automatically [OK]

Common Mistakes:

• Expecting string instead of JSON
• Confusing status code with response body
• Assuming error without code issues

4. What is wrong with this FastAPI health check endpoint code?

from fastapi import FastAPI
app = FastAPI()

@app.get('/health')
def health():
    return status: 'ok'

medium

A. Missing @app.post decorator

B. Syntax error in return statement

C. Function name must be 'health_check'

D. FastAPI app instance not created

Solution

1. Step 1: Inspect the return statement syntax

   The return line uses 'return status: 'ok'' which is invalid Python syntax; it should be a dictionary like {'status': 'ok'}.

2. Step 2: Check other parts for correctness

   The decorator @app.get is correct, function name can be anything, and app instance is created properly.

3. Final Answer:

   Syntax error in return statement -> Option B

4. Quick Check:

   Return dict with braces, not 'key: value' alone [OK]

Hint: Return a dict with braces, not 'key: value' alone [OK]

Common Mistakes:

• Writing return without braces for dict
• Using wrong decorator for GET endpoint
• Assuming function name is fixed

5. You want to create a health check endpoint in FastAPI that returns HTTP 200 with JSON {'status': 'ok'} if the app is healthy, but HTTP 503 with {'status': 'unhealthy'} if a database connection fails. Which approach correctly implements this?

hard

A. Use try-except inside the endpoint to check DB, return JSON with status code accordingly

B. Always return {'status': 'ok'} and rely on external monitoring for DB status

C. Create two endpoints: one for app status and one for DB status, no status codes

D. Raise an exception if DB fails, FastAPI returns 500 automatically

Solution

1. Step 1: Understand the requirement for conditional response

   The endpoint must check DB health and respond with different JSON and HTTP status codes based on that.

2. Step 2: Evaluate options for handling DB check and response

   Use try-except inside the endpoint to check DB, return JSON with status code accordingly uses try-except to check DB and returns JSON with correct status codes, matching the requirement. Others either ignore DB status or do not set proper codes.

3. Final Answer:

   Use try-except inside the endpoint to check DB, return JSON with status code accordingly -> Option A

4. Quick Check:

   Use try-except and return JSON with status codes [OK]

Hint: Use try-except and return JSON with proper HTTP status codes [OK]

Common Mistakes:

• Ignoring database health in the endpoint
• Not setting HTTP status codes explicitly
• Relying on default 500 instead of 503 for service unavailable