Gzip configuration (types, min_length) in Nginx - Step-by-Step Execution

Process Flow - Gzip configuration (types, min_length)

Start nginx config

↓

Enable gzip

↓

Set gzip_min_length

↓

Set gzip_types

↓

Request received

↓

Check content type

↓

Check content length

↓

Compress response

↓

Send response

This flow shows how nginx checks gzip settings: enabling gzip, setting minimum length, and types to compress, then deciding to compress or not based on request.

Execution Sample

Nginx

gzip on;
gzip_min_length 1000;
gzip_types text/plain application/json;

This config enables gzip, compresses responses only if size >= 1000 bytes, and only for specified content types.

Process Table

Step	Action	Content-Type	Content-Length	Condition	Result
1	Request received	text/plain	1500	Content-Type in gzip_types? Yes	Check content length
2	Check content length	text/plain	1500	Length >= gzip_min_length? Yes	Compress response
3	Send response	text/plain	1500	Compressed	Response sent compressed
4	Request received	image/png	2000	Content-Type in gzip_types? No	Send uncompressed
5	Send response	image/png	2000	Not compressed	Response sent uncompressed
6	Request received	application/json	800	Content-Type in gzip_types? Yes	Check content length
7	Check content length	application/json	800	Length >= gzip_min_length? No	Send uncompressed
8	Send response	application/json	800	Not compressed	Response sent uncompressed

💡 Requests processed based on content type and length compared to gzip settings.

Status Tracker

Variable	Start	After Request 1	After Request 2	After Request 3
gzip	off	on	on	on
gzip_min_length	0	1000	1000	1000
gzip_types	none	text/plain application/json	text/plain application/json	text/plain application/json
Content-Type	none	text/plain	image/png	application/json
Content-Length	0	1500	2000	800
Compressed	false	true	false	false

Key Moments - 3 Insights

Why does nginx not compress the image/png response even though its size is large?

Because image/png is not listed in gzip_types (see execution_table row 4), nginx skips compression for that content type.

What happens if the content length is less than gzip_min_length?

Nginx sends the response uncompressed (see execution_table rows 6-8), even if the content type matches gzip_types.

Does enabling gzip alone guarantee compression of all responses?

No, gzip must be enabled, and the response must meet both content type and minimum length conditions (see execution_table rows 1-3).

Visual Quiz - 3 Questions

Look at the execution table, at which step is the response compressed for a text/plain content type?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Check the 'Result' column for 'Response sent compressed' for text/plain content type.

According to the variable tracker, what is the value of gzip_min_length after configuration?

A 0

B 500

C 1000

D 1500

💡 Hint

Look at the 'gzip_min_length' row after 'After Request 1' in variable_tracker.

If gzip_types included 'image/png', what would change in the execution table for step 4?

A Response would be compressed

B Response would still be uncompressed

C Content length would change

D Request would be rejected

💡 Hint

Refer to step 4 where content type is image/png and compression depends on gzip_types.

Concept Snapshot

nginx gzip config:
gzip on; # enable gzip
gzip_min_length 1000; # min size to compress
gzip_types text/plain application/json; # compress only these types
Requests smaller or types not listed are sent uncompressed.

Full Transcript

This visual execution shows how nginx decides to compress responses using gzip. First, gzip must be enabled. Then nginx checks if the response content type matches the gzip_types list. If yes, it checks if the response size is at least gzip_min_length bytes. Only then does it compress the response. Otherwise, it sends the response uncompressed. For example, a text/plain response of 1500 bytes is compressed, but an image/png response is not compressed because it is not in gzip_types. Also, a small application/json response under 1000 bytes is not compressed. This helps save CPU by compressing only useful responses.