Keepalive connections in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a keepalive connection in nginx?

A keepalive connection allows nginx to reuse the same TCP connection for multiple requests between the client and server, reducing the overhead of opening new connections.

beginner

Which nginx directive enables keepalive connections for upstream servers?

The directive keepalive inside the upstream block enables keepalive connections to upstream servers.

intermediate

What does the keepalive_timeout directive control in nginx?

It controls how long nginx keeps an idle keepalive connection open before closing it.

intermediate

How does enabling keepalive connections improve performance?

It reduces the time and CPU needed to establish new TCP connections by reusing existing ones, leading to faster response times and less resource use.

beginner

What is the default behavior of nginx regarding keepalive connections if not configured?

By default, nginx closes the connection after each request unless keepalive is explicitly enabled.

Which directive in nginx enables keepalive connections to upstream servers?

A keepalive

B proxy_pass

C listen

D server_name

The keepalive directive inside the upstream block enables keepalive connections.

What is the main benefit of using keepalive connections in nginx?

A Increasing the number of open connections

B Encrypting data automatically

C Blocking slow clients

D Reusing TCP connections to reduce overhead

Keepalive connections reuse TCP connections, reducing the overhead of opening new ones.

Which directive controls how long nginx keeps an idle keepalive connection open?

A worker_processes

B client_max_body_size

C keepalive_timeout

D proxy_connect_timeout

keepalive_timeout sets the idle time before closing a keepalive connection.

If keepalive is not enabled, what does nginx do after serving a request?

A Keeps the connection open indefinitely

B Closes the connection

C Sends a redirect

D Logs an error

By default, nginx closes the connection after each request unless keepalive is enabled.

Where should the keepalive directive be placed to enable connection reuse to backend servers?

A Inside the upstream block

B Inside the server block

C Inside the location block

D Inside the http block

The keepalive directive must be inside the upstream block to enable reuse of connections to backend servers.

Explain what keepalive connections are in nginx and why they are useful.

Think about how opening new connections affects speed and resources.

Describe how to configure keepalive connections for upstream servers in nginx.

Focus on where and what directives to use.

Practice

1. What is the main benefit of using keepalive connections in nginx?

easy

A. They disable caching on the server.

B. They close connections immediately after each request.

C. They increase the number of open connections indefinitely.

D. They reuse the same connection for multiple requests, improving speed.

Solution

1. Step 1: Understand what keepalive connections do

   Keepalive connections allow the same connection to be reused for multiple requests instead of opening a new one each time.

2. Step 2: Identify the benefit of reusing connections

   Reusing connections reduces the time and resources needed to establish new connections, thus improving speed and reducing server load.

3. Final Answer:

   They reuse the same connection for multiple requests, improving speed. -> Option D

4. Quick Check:

   Keepalive = reuse connection for speed [OK]

Hint: Keepalive means reuse connection to speed up requests [OK]

Common Mistakes:

• Thinking keepalive closes connections immediately
• Believing keepalive increases open connections endlessly
• Confusing keepalive with caching

2. Which of the following is the correct syntax to set the keepalive timeout to 30 seconds in nginx?

easy

A. keepalive_timeout 30s

B. keepalive_timeout 30;

C. keepalive_timeout: 30s;

D. keepalive_timeout = 30;

Solution

1. Step 1: Recall nginx directive syntax

   Nginx directives use the format: directive_name value; without equal signs or colons.

2. Step 2: Check the correct value format for time

   Timeout values in nginx can be specified as numbers (seconds) without units or with units like 's'. Both are accepted, but the common practice is just a number for seconds.

3. Final Answer:

   keepalive_timeout 30; -> Option B

4. Quick Check:

   Directive syntax = name value; no '=' or ':' [OK]

Hint: Nginx directives use 'name value;' syntax without '=' [OK]

Common Mistakes:

• Using '=' sign in directive
• Adding colon ':' after directive name
• Adding units like 's' unnecessarily

3. Given this nginx configuration snippet:

keepalive_timeout 10;
keepalive_requests 100;

What happens after 100 requests on the same keepalive connection?

medium

A. The connection is closed and a new one is opened for the next request.

B. The connection stays open indefinitely.

C. The server resets the timeout to 10 seconds again.

D. The connection is closed immediately after the first request.

Solution

1. Step 1: Understand keepalive_requests directive

   This directive limits how many requests can be sent over one keepalive connection before it closes.

2. Step 2: Apply the limit of 100 requests

   After 100 requests, nginx closes the connection and opens a new one for the next request to avoid stale connections.

3. Final Answer:

   The connection is closed and a new one is opened for the next request. -> Option A

4. Quick Check:

   keepalive_requests = max requests per connection [OK]

Hint: keepalive_requests limits requests per connection [OK]

Common Mistakes:

• Thinking connection stays open forever
• Confusing timeout with request count
• Assuming connection closes after first request

4. You set keepalive_timeout 20; but clients report connections close too quickly. Which is the likely mistake?

medium

A. The keepalive_requests is set to 1, closing after one request.

B. The timeout value is too low for client needs.

C. You forgot to reload nginx after changing config.

D. The server is running an old nginx version without keepalive support.

Solution

1. Step 1: Check common reasons for config changes not applying

   If nginx is not reloaded or restarted after config changes, old settings remain active.

2. Step 2: Confirm reload necessity

   After changing keepalive_timeout, nginx must be reloaded with nginx -s reload or restarted to apply changes.

3. Final Answer:

   You forgot to reload nginx after changing config. -> Option C

4. Quick Check:

   Config changes need reload to apply [OK]

Hint: Reload nginx after config changes to apply them [OK]

Common Mistakes:

• Assuming timeout value alone fixes issue
• Ignoring need to reload nginx
• Blaming nginx version without checking

5. You want to optimize nginx for many short requests by keeping connections alive but closing them after 15 seconds or 50 requests, whichever comes first. Which configuration is correct?

hard

A. keepalive_timeout 15;\nkeepalive_requests 50;

B. keepalive_timeout 50;\nkeepalive_requests 15;

C. keepalive_timeout 15s;\nkeepalive_requests 50s;

D. keepalive_timeout 15s;\nkeepalive_requests 50; keepalive_disable none;

Solution

1. Step 1: Set keepalive_timeout to 15 seconds

   This controls how long a connection stays open waiting for new requests.

2. Step 2: Set keepalive_requests to 50

   This limits the number of requests per connection before closing it.

3. Step 3: Verify correct syntax and values

   keepalive_timeout 15;\nkeepalive_requests 50; uses correct syntax and values matching the requirement: 15 seconds timeout and 50 requests limit.

4. Final Answer:

   keepalive_timeout 15;\nkeepalive_requests 50; -> Option A

5. Quick Check:

   Timeout 15 + Requests 50 = correct config [OK]

Hint: Timeout sets seconds, requests sets max requests per connection [OK]

Common Mistakes:

• Swapping timeout and requests values
• Adding units to keepalive_requests
• Using invalid directives like keepalive_disable