Connection limiting (limit_conn) in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the limit_conn directive do in nginx?

It limits the number of simultaneous connections for a defined key, such as an IP address, to control traffic and prevent overload.

intermediate

How do you define a shared memory zone for connection limiting in nginx?

Use limit_conn_zone $variable zone=name:size; to create a zone that tracks connections by the variable (e.g., $binary_remote_addr).

intermediate

Example: What does this configuration do?<br>

limit_conn_zone $binary_remote_addr zone=addr:10m;<br>limit_conn addr 5;

It limits each client IP address to a maximum of 5 simultaneous connections using a 10MB shared memory zone named 'addr'.

beginner

What happens when a client exceeds the connection limit set by limit_conn?

nginx returns a 503 Service Unavailable error to the client, refusing additional connections beyond the limit.

beginner

Why is connection limiting useful in a web server?

It helps protect the server from overload, prevents abuse, and ensures fair resource use among clients.

Which directive creates a shared memory zone for connection limiting in nginx?

A limit_conn_zone

B limit_conn

C limit_rate

D limit_req_zone

The limit_conn_zone directive defines the shared memory zone to track connections.

What variable is commonly used to limit connections per client IP in nginx?

A $binary_remote_addr

B $request_uri

C $host

D $server_name

$binary_remote_addr represents the client IP in a compact form for connection limiting.

If you set limit_conn addr 10;, what does it mean?

A Allow 10 connections total to the server

B Allow 10 connections per IP address

C Allow 10 requests per second

D Allow 10 connections per server block

It limits each key in the zone 'addr' (usually IP) to 10 simultaneous connections.

What response code does nginx send when connection limit is exceeded?

A 404 Not Found

B 500 Internal Server Error

C 503 Service Unavailable

D 429 Too Many Requests

nginx returns 503 Service Unavailable when connection limits are exceeded.

Which of these is NOT a benefit of connection limiting?

A Prevent server overload

B Improve server security

C Ensure fair resource use

D Increase server CPU speed

Connection limiting does not affect CPU speed; it controls traffic to protect resources.

Explain how to configure nginx to limit the number of simultaneous connections per client IP.

Think about tracking IPs and setting max connections.

Describe what happens when a client exceeds the connection limit set by nginx's limit_conn directive.

What does the server do when too many connections come from one client?