Rewrite directive in Nginx - Step-by-Step Execution

Process Flow - Rewrite directive

Request comes in

↓

Check rewrite rule pattern

↓

Rewrite URL

↓

Redirect or internal rewrite

↓

Send response

The rewrite directive checks if the incoming URL matches a pattern. If yes, it rewrites the URL and either redirects or internally rewrites before sending the response.

Execution Sample

Nginx

server {
  listen 80;
  rewrite ^/oldpath/(.*)$ /newpath/$1 permanent;
}

This config rewrites URLs starting with /oldpath/ to /newpath/ with a permanent redirect.

Process Table

Step	Incoming URL	Rewrite Pattern	Match Result	Action	Resulting URL
1	/oldpath/page1	^/oldpath/(.*)$	Match	Rewrite with permanent redirect	/newpath/page1
2	/oldpath/page2	^/oldpath/(.*)$	Match	Rewrite with permanent redirect	/newpath/page2
3	/otherpath/page	^/oldpath/(.*)$	No Match	Serve original URL	/otherpath/page

💡 Execution stops after rewrite or serving original URL based on match.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
Incoming URL	/oldpath/page1	/oldpath/page2	/otherpath/page	/otherpath/page
Resulting URL	N/A	/newpath/page1	/newpath/page2	/otherpath/page

Key Moments - 2 Insights

Why does the URL change only when the pattern matches?

Because the rewrite directive only applies its action if the incoming URL matches the specified pattern, as shown in execution_table rows 1 and 3.

What does 'permanent' mean in the rewrite directive?

'Permanent' means the server sends a 301 redirect telling the browser the URL has moved permanently, causing the browser to update the URL, as seen in the action column.

Visual Quiz - 3 Questions

Look at the execution table, what is the resulting URL at step 2?

A /newpath/page2

B /oldpath/page2

C /otherpath/page

D /newpath/page1

💡 Hint

Check the 'Resulting URL' column in row 2 of the execution_table.

At which step does the rewrite pattern NOT match the incoming URL?

A Step 1

B Step 2

C Step 3

D None

💡 Hint

Look at the 'Match Result' column in the execution_table.

If we remove 'permanent' from the rewrite directive, what changes in the execution?

A The URL is rewritten internally without redirecting the browser

B The URL will not change at all

C The server will return an error

D The rewrite pattern will not match

💡 Hint

Consider the meaning of 'permanent' in the action column of the execution_table.

Concept Snapshot

rewrite directive syntax:
rewrite regex replacement [flag];

Checks if URL matches regex.
If yes, rewrites URL to replacement.
Flags control redirect type (e.g., permanent = 301).
Used for URL changes or redirects.

Full Transcript

The nginx rewrite directive checks incoming URLs against a pattern. If the URL matches, it rewrites the URL to a new one. This can be an internal rewrite or a redirect. For example, URLs starting with /oldpath/ can be redirected permanently to /newpath/. If the URL does not match, it is served as is. The 'permanent' flag sends a 301 redirect to the browser. This process helps manage URL changes smoothly.