Why load balancing distributes traffic in Nginx - Visual Breakdown

Process Flow - Why load balancing distributes traffic

Client sends request

↓

Load Balancer receives request

↓

Select backend server based on algorithm

↓

Forward request to selected server

↓

Server processes request and responds

↓

Response sent back to client

Traffic from clients goes to the load balancer, which picks a backend server to handle each request, then forwards the request and returns the server's response.

Execution Sample

Nginx

upstream backend {
    server 192.168.1.10;
    server 192.168.1.11;
}

server {
    location / {
        proxy_pass http://backend;
    }
}

This Nginx config defines two backend servers and forwards incoming requests to them using load balancing.

Process Table

Step	Client Request	Load Balancer Action	Selected Server	Request Forwarded	Response Sent
1	Request 1	Receives request	192.168.1.10	Forwarded to 192.168.1.10	Response from 192.168.1.10
2	Request 2	Receives request	192.168.1.11	Forwarded to 192.168.1.11	Response from 192.168.1.11
3	Request 3	Receives request	192.168.1.10	Forwarded to 192.168.1.10	Response from 192.168.1.10
4	Request 4	Receives request	192.168.1.11	Forwarded to 192.168.1.11	Response from 192.168.1.11
5	Request 5	Receives request	192.168.1.10	Forwarded to 192.168.1.10	Response from 192.168.1.10
Exit	No more requests	Stops forwarding	-	-	-

💡 No more client requests to distribute

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Selected Server	-	192.168.1.10	192.168.1.11	192.168.1.10	192.168.1.11	192.168.1.10	-

Key Moments - 2 Insights

Why does the load balancer pick different servers for each request?

The load balancer uses a round-robin method (see execution_table rows 1-5) to evenly distribute requests between servers, preventing overload on one server.

What happens if one server is slow or down?

Nginx can detect server health and skip slow or down servers, so requests go only to healthy servers, ensuring smooth traffic flow.

Visual Quiz - 3 Questions

Look at the execution table, which server handles the 3rd request?

A 192.168.1.11

B 192.168.1.10

C 192.168.1.12

D No server

💡 Hint

Check the 'Selected Server' column at Step 3 in the execution_table

At which step does the load balancer stop forwarding requests?

A Exit step

B Step 5

C Step 4

D Step 3

💡 Hint

Look at the 'Step' column and the exit_note in the execution_table

If a third server 192.168.1.12 is added, how would the selected server sequence change?

A It would pick servers randomly

B It would still use only the first two servers

C It would alternate between the three servers in order

D It would send all requests to 192.168.1.12

💡 Hint

Think about round-robin distribution and how adding a server affects the sequence in variable_tracker

Concept Snapshot

Load balancing in Nginx forwards client requests to multiple backend servers.
It uses algorithms like round-robin to distribute traffic evenly.
This prevents any single server from getting overloaded.
If a server is down, Nginx skips it to keep traffic flowing.
Config uses 'upstream' block and 'proxy_pass' directive.

Full Transcript

Load balancing distributes incoming client requests across multiple backend servers. The load balancer receives each request and selects a server to handle it, often using a round-robin method to keep traffic balanced. This prevents any one server from becoming overloaded and improves reliability. In Nginx, you define backend servers in an upstream block and forward requests using proxy_pass. The load balancer forwards the request to the chosen server, which processes it and sends back the response. If a server is down, Nginx can detect this and skip it, ensuring smooth service. The execution table shows how requests are distributed step-by-step, alternating between two servers.