Burst and nodelay options in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the burst option do in nginx rate limiting?

The burst option allows a temporary extra number of requests to pass beyond the set rate limit. It acts like a small buffer for sudden spikes in traffic.

beginner

Explain the nodelay option in nginx rate limiting.

The nodelay option lets requests in the burst queue pass immediately without delay. Without it, requests in the burst queue are delayed to match the rate limit.

intermediate

How do burst and nodelay work together in nginx?

The burst option allows extra requests to queue up temporarily. The nodelay option makes those queued requests pass instantly instead of waiting, helping handle sudden traffic bursts smoothly.

intermediate

What happens if you set burst without nodelay in nginx?

Requests above the rate limit are queued up to the burst size but are delayed to match the rate limit speed. This can cause some requests to wait before being processed.

beginner

Give a simple nginx configuration snippet using burst and nodelay.

limit_req_zone $binary_remote_addr zone=mylimit:10m rate=5r/s; server { location /api/ { limit_req zone=mylimit burst=10 nodelay; } }

What does the burst option control in nginx rate limiting?

A Timeout for requests

B Number of extra requests allowed temporarily beyond the rate limit

C Maximum number of concurrent connections

D Size of the request body

The burst option allows a temporary buffer of extra requests beyond the set rate limit.

What effect does the nodelay option have when used with burst?

A Allows burst requests to pass immediately without delay

B Delays all requests to match the rate limit

C Blocks burst requests

D Increases the rate limit permanently

nodelay makes burst requests pass instantly instead of waiting.

If burst is set to 5 and nodelay is not used, what happens to the 6th request arriving quickly?

A It is rejected immediately

B It passes instantly

C It is delayed to fit the rate limit

D It increases the burst size

Without nodelay, burst requests beyond the limit are delayed to match the rate.

Which directive defines the rate limit zone used with burst and nodelay?

A server_name

B limit_conn_zone

C proxy_pass

D limit_req_zone

limit_req_zone defines the shared memory zone and rate for limiting requests.

Why would you use burst and nodelay together?

A To allow sudden traffic spikes without delay

B To reject all extra requests

C To slow down all requests

D To increase server memory

Together they allow extra requests to pass immediately, handling traffic spikes smoothly.

Describe how the burst and nodelay options affect request handling in nginx rate limiting.

Think about how nginx handles sudden spikes in requests.

Write a simple nginx configuration snippet that limits requests to 10 per second with a burst of 20 and uses nodelay.

Use $binary_remote_addr for the zone key.

Practice

1. What does the burst option do in nginx rate limiting?

easy

A. Processes all requests without any limit

B. Immediately rejects extra requests beyond the limit

C. Allows extra requests to wait in a queue before being processed

D. Delays all requests by a fixed time

Solution

1. Step 1: Understand the purpose of burst

   The burst option in nginx allows extra requests that exceed the rate limit to be queued temporarily instead of being rejected immediately.

2. Step 2: Compare with other options

   Unlike rejecting or delaying all requests, burst specifically queues extra requests to handle traffic spikes smoothly.

3. Final Answer:

   Allows extra requests to wait in a queue before being processed -> Option C

4. Quick Check:

   Burst = queue extra requests [OK]

Hint: Burst queues extra requests to handle spikes smoothly [OK]

Common Mistakes:

• Thinking burst rejects extra requests immediately
• Confusing burst with fixed delay
• Assuming burst processes all requests without limit

2. Which is the correct syntax to enable burst with 10 requests and nodelay in nginx?

easy

A. limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit burst=10 nodelay;

B. limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit burst=10 delay;

C. limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit burst=10;

D. limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit nodelay burst=10;

Solution

1. Step 1: Identify correct order and keywords

   The correct syntax places burst=10 followed by nodelay without extra keywords like delay.

2. Step 2: Validate syntax correctness

   limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit burst=10 nodelay; correctly uses limit_req_zone and limit_req directives with proper parameters and order.

3. Final Answer:

   limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit burst=10 nodelay; -> Option A

4. Quick Check:

   Syntax with burst=10 and nodelay = limit_req_zone $binary_remote_addr zone=mylimit:10m rate=1r/s; limit_req zone=mylimit burst=10 nodelay; [OK]

Hint: Use burst=number before nodelay in limit_req [OK]

Common Mistakes:

• Using 'delay' instead of 'nodelay'
• Placing nodelay before burst
• Omitting limit_req_zone directive

3. Given this nginx config snippet:

limit_req_zone $binary_remote_addr zone=one:10m rate=1r/s;
limit_req zone=one burst=3 nodelay;

What happens if 5 requests arrive instantly from the same IP?

medium

A. All 5 requests are processed immediately

B. First 4 requests processed immediately, 5th rejected

C. First request processed immediately, next 4 delayed

D. Only 1 request processed, others rejected

Solution

1. Step 1: Understand rate and burst limits

   The rate is 1 request per second, burst allows 3 extra requests queued, and nodelay means queued requests run immediately.

2. Step 2: Analyze 5 instant requests

   The first request is within rate limit, next 3 fit in burst queue and run immediately due to nodelay, the 5th exceeds burst and is rejected.

3. Final Answer:

   First 4 requests processed immediately, 5th rejected -> Option B

4. Quick Check:

   Burst=3 + nodelay means 4 immediate, 5th rejected [OK]

Hint: Burst + nodelay = burst requests processed immediately [OK]

Common Mistakes:

• Assuming all 5 requests pass immediately
• Thinking requests after burst are delayed, not rejected
• Ignoring nodelay effect

4. You configured burst=5 but your nginx still rejects extra requests immediately. What is the likely cause?

medium

A. You forgot to add the nodelay option

B. The limit_req_zone directive is missing

C. The burst value must be less than 5

D. You need to restart nginx twice

Solution

1. Step 1: Check burst behavior without nodelay

   Without nodelay, burst requests are delayed, not processed immediately, but if delay is too long, clients may see rejections.

2. Step 2: Identify missing nodelay effect

   If extra requests are rejected immediately despite burst, likely nodelay is missing, causing strict rate enforcement.

3. Final Answer:

   You forgot to add the nodelay option -> Option A

4. Quick Check:

   Missing nodelay causes immediate rejection despite burst [OK]

Hint: Add nodelay to process burst requests immediately [OK]

Common Mistakes:

• Assuming burst alone allows immediate processing
• Thinking burst must be less than 5
• Believing multiple restarts fix config issues

5. You want to handle sudden spikes of up to 20 extra requests per second without delay, but reject any beyond that. Which nginx config snippet achieves this?

hard

A. limit_req_zone $binary_remote_addr zone=spike:10m rate=20r/s;
limit_req zone=spike burst=5 nodelay;

B. limit_req_zone $binary_remote_addr zone=spike:10m rate=25r/s;
limit_req zone=spike burst=0;

C. limit_req_zone $binary_remote_addr zone=spike:10m rate=5r/s;
limit_req zone=spike burst=0 nodelay;

D. limit_req_zone $binary_remote_addr zone=spike:10m rate=5r/s;
limit_req zone=spike burst=20 nodelay;

Solution

1. Step 1: Set base rate and burst for spikes

   The base rate is 5 requests per second, and burst=20 allows 20 extra requests queued.

2. Step 2: Use nodelay to process burst immediately

   Adding nodelay ensures the burst requests are processed right away without delay.

3. Step 3: Confirm rejection beyond burst

   Requests beyond burst=20 will be rejected, matching the requirement.

4. Final Answer:

   limit_req_zone $binary_remote_addr zone=spike:10m rate=5r/s; limit_req zone=spike burst=20 nodelay; -> Option D

5. Quick Check:

   Rate=5r/s + burst=20 + nodelay = limit_req_zone $binary_remote_addr zone=spike:10m rate=5r/s; limit_req zone=spike burst=20 nodelay; [OK]

Hint: Set burst high with nodelay to handle spikes immediately [OK]

Common Mistakes:

• Setting burst too low for spikes
• Omitting nodelay causing delays
• Setting rate too high ignoring burst