API routing with location blocks in Nginx - Step-by-Step Execution

Process Flow - API routing with location blocks

Client sends HTTP request

↓

Nginx receives request

↓

Check location blocks in order

↓

Match found?

No→Return 404 or default

Yes↓

Route request to matched location

↓

Serve response from backend or static files

Nginx receives a request, checks location blocks in order, routes to the matching block, or returns default if none match.

Execution Sample

Nginx

server {
  listen 80;
  location /api/ {
    proxy_pass http://backend_api;
  }
  location / {
    root /var/www/html;
  }
}

Routes requests starting with /api/ to backend_api, others serve static files from /var/www/html.

Process Table

Step	Request URI	Location Block Checked	Match Result	Action Taken
1	/api/users	location /api/	Match	Proxy to backend_api
2	/api/users	location /	Not checked (first match found)	No action
3	/home	location /api/	No match	Check next location
4	/home	location /	Match	Serve static files from /var/www/html
5	/unknown	location /api/	No match	Check next location
6	/unknown	location /	Match	Serve static files from /var/www/html
7	/notfound	location /api/	No match	Check next location
8	/notfound	location /	Match	Serve static files from /var/www/html

💡 Request routed to first matching location block or default if none match.

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 4	Final
Request URI		/api/users	/home	/home	/home
Matched Location	None	/api/	None	/	/
Action	None	Proxy to backend_api	None	Serve static files	Serve static files

Key Moments - 3 Insights

Why does Nginx stop checking location blocks after the first match?

Nginx uses the first matching location block to route the request, so once a match is found (see Step 1), it stops checking others to improve performance.

What happens if no location block matches the request URI?

If no location matches, Nginx uses the default server behavior, often returning a 404 error or serving the root location if defined (not shown in this example).

Why does /home match the location / block and not /api/?

Because /home does not start with /api/, so the /api/ location block does not match (Step 3), but / matches all URIs, so it matches at Step 4.

Visual Quiz - 3 Questions

Look at the execution table, what action is taken for the request URI '/api/users' at Step 1?

A Serve static files

B Return 404 error

C Proxy to backend_api

D Check next location block

💡 Hint

Check the 'Action Taken' column at Step 1 in the execution_table.

At which step does the request URI '/home' match the location block '/'?

A Step 3

B Step 4

C Step 2

D Step 1

💡 Hint

Look at the 'Match Result' column for '/home' in the execution_table.

If a new location block 'location /api/v2/' is added before 'location /api/', which request URI would match it first?

A /api/v2/items

B /home

C /api/users

D /api/

💡 Hint

Consider prefix matching order and the execution flow of location blocks.

Concept Snapshot

Nginx API routing uses location blocks to match request URIs.
The first matching location block handles the request.
Use prefix matching like 'location /api/' for API routes.
Order matters: more specific blocks should come first.
Unmatched requests go to default or return 404.

Full Transcript

When a client sends an HTTP request, Nginx receives it and checks its location blocks in order. It compares the request URI to each location block's prefix. Once it finds a match, it routes the request accordingly, such as proxying to a backend API or serving static files. If no location matches, Nginx returns a default response or error. For example, requests starting with '/api/' go to the backend API, while others serve static content. This process stops at the first match to keep routing efficient.