Brotli compression in Nginx - Step-by-Step Execution

Process Flow - Brotli compression

Client sends HTTP request

↓

Nginx receives request

↓

Check if Brotli module enabled?

No→Serve uncompressed content

Yes↓

Check if client supports Brotli (Accept-Encoding)

↓

Compress response

↓

Send compressed response to client

Nginx checks if Brotli is enabled and if the client supports it, then compresses the response before sending.

Execution Sample

Nginx

brotli on;
brotli_comp_level 5;
brotli_types text/html text/css application/javascript;

Enable Brotli compression in nginx with level 5 for HTML, CSS, and JS files.

Process Table

Step	Action	Condition	Result	Response Sent
1	Receive HTTP request	N/A	Request received	No response yet
2	Check if Brotli enabled	brotli on?	Yes	No response yet
3	Check client Accept-Encoding	Includes 'br'?	Yes	No response yet
4	Compress response	Content type matches brotli_types?	Yes	No response yet
5	Send response	N/A	Response sent with Content-Encoding: br	Compressed content sent
6	End	N/A	Request complete	Process ends

💡 Process ends after sending compressed response or uncompressed if conditions not met

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
brotli_enabled	undefined	true	true	true	true
client_accepts_brotli	undefined	undefined	true	true	true
response_compressed	false	false	false	true	true
response_sent	false	false	false	false	true

Key Moments - 2 Insights

Why does nginx send uncompressed content even if Brotli is enabled?

Because the client’s Accept-Encoding header does not include 'br', as shown in execution_table step 3 where condition is No, leading to uncompressed response.

What happens if the content type is not listed in brotli_types?

Nginx will not compress the response even if Brotli is enabled and client supports it, as in step 4 where content type check fails, so response is sent uncompressed.

Visual Quiz - 3 Questions

Look at the execution table, at which step does nginx decide to compress the response?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'Action' and 'Result' columns in step 4 for compression decision

According to variable_tracker, what is the value of 'response_compressed' after Step 3?

A false

B undefined

C true

D null

💡 Hint

Look at the 'response_compressed' row under 'After Step 3' column

If the client does not support Brotli, how does the execution_table change?

A Step 4 compresses anyway

B Step 3 condition is No and response is uncompressed

C Step 5 sends compressed response

D Step 2 disables Brotli

💡 Hint

Refer to step 3 condition and response sent columns

Concept Snapshot

Enable Brotli in nginx with 'brotli on;'.
Set compression level with 'brotli_comp_level'.
Specify file types in 'brotli_types'.
Nginx compresses only if client supports 'br' encoding.
Compressed response sent with 'Content-Encoding: br'.

Full Transcript

Brotli compression in nginx works by first enabling the module with 'brotli on;'. When a client sends a request, nginx checks if Brotli is enabled and if the client supports Brotli compression via the Accept-Encoding header. If both conditions are true and the content type matches configured types, nginx compresses the response using Brotli and sends it with the appropriate header. Otherwise, it sends the response uncompressed. This process ensures efficient delivery of web content when supported.