Performance bottleneck identification in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check the current active connections in NGINX.

Nginx

curl http://localhost/nginx_status | grep [1]

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

AActive

BConnections

CRequests

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Connections' alone does not match the exact line.

Using 'Requests' shows total requests, not active connections.

The Active keyword shows the number of active connections in the NGINX status output.

2fill in blank

medium

Complete the code to enable the stub_status module in NGINX configuration.

Nginx

location /nginx_status {
    stub_status [1];
    allow 127.0.0.1;
    deny all;
}

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

Aon

Boff

Cenable

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'off' disables the module.

Using 'enable' or 'true' are invalid directives.

The stub_status on; directive enables the status module in NGINX.

3fill in blank

hard

Fix the error in the NGINX log format to include request time.

Nginx

log_format main '$remote_addr - $remote_user [$time_local] "$request" '
                 '$status $body_bytes_sent "$http_referer" '
                 '"$http_user_agent" $[1]; 

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

Arequest_length_time

Brequest_time

Crequest_length

Drequest_duration

Attempts:

3 left

💡 Hint

Common Mistakes

Using '$request_duration' or '$request_length' are invalid variables.

Misspelling the variable causes logging errors.

The variable $request_time logs the time spent processing the request.

4fill in blank

hard

Fill both blanks to create a map that sets a variable based on request time threshold.

Nginx

map $request_time $slow_request {
    default [1];
    ~^[3-9]\.|^[1-9][0-9]+ [2];
}

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

A0

B1

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'true' or 'false' instead of numeric 0 or 1.

Reversing the default and matched values.

The map sets $slow_request to 0 by default and 1 if the request time is 3 seconds or more.

5fill in blank

hard

Fill all three blanks to log slow requests only.

Nginx

access_log /var/log/nginx/slow.log combined if=[1];

map $request_time $slow_request {
    default [2];
    ~^[3-9]\.|^[1-9][0-9]+ [3];
}

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

A$slow_request

B0

C1

D$request_time

Attempts:

3 left

💡 Hint

Common Mistakes

Using '$request_time' directly in access_log condition.

Mixing up default and matched values in the map.

The access log uses if=$slow_request to log only slow requests. The map sets default to 0 (not slow) and 1 for slow requests.

Practice

1. What is the primary purpose of enabling the stub_status module in nginx?

easy

A. To monitor active connections and request statistics

B. To enable SSL encryption for secure connections

C. To cache static files for faster delivery

D. To compress HTTP responses automatically

Solution

1. Step 1: Understand the stub_status module

   The stub_status module provides a simple way to get real-time statistics about nginx such as active connections and request counts.

2. Step 2: Identify its monitoring role

   It does not handle SSL, caching, or compression but focuses on performance metrics.

3. Final Answer:

   To monitor active connections and request statistics -> Option A

4. Quick Check:

   stub_status = monitor connections and requests [OK]

Hint: stub_status shows live connection and request stats [OK]

Common Mistakes:

• Confusing stub_status with SSL or caching modules
• Thinking it compresses responses
• Assuming it improves performance directly

2. Which of the following nginx configuration snippets correctly enables the stub_status page at /nginx_status?

easy

A. location /nginx_status { stub_status on; allow 127.0.0.1; deny all; }

B. location /nginx_status { stub_status; allow 127.0.0.1; deny all; }

C. location /nginx_status { stub_status on; allow all; }

D. location /nginx_status { status_stub on; allow 127.0.0.1; deny all; }

Solution

1. Step 1: Recall correct stub_status syntax

   The directive to enable stub_status is simply stub_status; without 'on'.

2. Step 2: Check access control correctness

   Allowing 127.0.0.1 and denying others is correct for security.

3. Final Answer:

   location /nginx_status { stub_status; allow 127.0.0.1; deny all; } -> Option B

4. Quick Check:

   stub_status directive has no 'on' [OK]

Hint: stub_status directive has no 'on' keyword [OK]

Common Mistakes:

• Adding 'on' after stub_status
• Using wrong directive name like status_stub
• Allowing all IPs without restriction

3. Given this nginx log excerpt showing many slow requests, which metric indicates a potential bottleneck?

medium

A. High number of 200 status codes

B. Low bytes_sent values

C. Frequent GET requests

D. High request_time values in access logs

Solution

1. Step 1: Understand request_time meaning

   The request_time shows how long nginx took to process a request; high values mean slow responses.

2. Step 2: Analyze other metrics

   Low bytes_sent or many 200 codes do not indicate slowness; frequent GETs are normal traffic.

3. Final Answer:

   High request_time values in access logs -> Option D

4. Quick Check:

   High request_time = slow requests [OK]

Hint: Look for high request_time to spot slow requests [OK]

Common Mistakes:

• Confusing status codes with performance
• Assuming bytes_sent relates to speed
• Ignoring request_time metric

4. You added the stub_status location but get a 404 error when accessing /nginx_status. What is the most likely cause?

medium

A. The location block syntax is incorrect with extra semicolons

B. The server block is missing the listen directive

C. The stub_status module is not compiled or enabled in nginx

D. The allow directive is missing

Solution

1. Step 1: Check module availability

   If stub_status is not compiled into nginx, the location will not work and return 404.

2. Step 2: Verify other config parts

   Incorrect syntax or missing listen usually cause config errors, not 404. Missing allow causes access denied, not 404.

3. Final Answer:

   The stub_status module is not compiled or enabled in nginx -> Option C

4. Quick Check:

   Missing stub_status module = 404 error [OK]

Hint: 404 on stub_status means module missing or disabled [OK]

Common Mistakes:

• Assuming syntax errors cause 404
• Confusing 404 with access denied errors
• Ignoring module compilation status

5. You want to identify if nginx worker processes are a bottleneck under high load. Which combined approach helps you best diagnose this?

hard

A. Check stub_status active connections and use top to monitor worker CPU usage

B. Only check nginx error logs for worker crashes

C. Increase worker_processes blindly without monitoring

D. Disable access logs to reduce disk usage

Solution

1. Step 1: Use stub_status for connection metrics

   stub_status shows active connections and requests, indicating load on workers.

2. Step 2: Monitor worker CPU usage with system tools

   Using top or similar tools shows if workers are maxing CPU, a sign of bottleneck.

3. Step 3: Combine metrics for diagnosis

   Both metrics together reveal if workers are overloaded or if other issues exist.

4. Final Answer:

   Check stub_status active connections and use top to monitor worker CPU usage -> Option A

5. Quick Check:

   Combine stub_status + CPU monitoring = diagnose bottleneck [OK]

Hint: Combine stub_status and CPU tools to find worker bottlenecks [OK]

Common Mistakes:

• Ignoring CPU usage of workers
• Changing config without data
• Relying only on logs or disabling logs