Gzip compression in Nginx - Step-by-Step Execution

Process Flow - Gzip compression

Client sends HTTP request

↓

Nginx receives request

↓

Check if gzip is enabled?

No→Send response uncompressed

Yes↓

Compress response with gzip

↓

Add Content-Encoding: gzip header

↓

Send compressed response to client

Nginx checks if gzip compression is enabled for the response. If yes, it compresses the response and adds the proper header before sending it to the client.

Execution Sample

Nginx

gzip on;
gzip_types text/plain application/json;

location / {
  proxy_pass http://backend;
}

This config enables gzip compression for text and JSON responses proxied to the backend.

Process Table

Step	Action	Condition	Result	Response Header	Response Body
1	Receive client request	N/A	Request accepted	N/A	N/A
2	Check gzip setting	gzip on?	Yes	N/A	N/A
3	Check content type	Is content type in gzip_types?	Yes (application/json)	N/A	N/A
4	Compress response	N/A	Response compressed	Content-Encoding: gzip	Compressed data
5	Send response	N/A	Compressed response sent	Content-Encoding: gzip	Compressed data
6	End	N/A	Request complete	N/A	N/A

💡 Nginx sends compressed response because gzip is enabled and content type matches gzip_types.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
gzip	off	on	on	on	on
content_type	unknown	unknown	application/json	application/json	application/json
response_compressed	false	false	false	true	true
response_header	none	none	none	Content-Encoding: gzip	Content-Encoding: gzip

Key Moments - 3 Insights

Why does nginx only compress some responses and not all?

Nginx compresses only if gzip is enabled and the response content type matches the types listed in gzip_types, as shown in steps 2 and 3 of the execution_table.

What happens if gzip is off in the config?

If gzip is off, nginx skips compression and sends the response uncompressed, as the flow exits at step 2 in the execution_table.

Why is the Content-Encoding header important?

It tells the client the response is compressed with gzip, so the client knows to decompress it. This header is added in step 4 of the execution_table.

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 'Condition' column where nginx checks content type before compressing.

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

A unknown

B true

C false

D none

💡 Hint

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

If gzip was set to off, how would the execution_table change?

A Step 2 would show 'No' and skip compression steps

B Step 4 would compress anyway

C Content-Encoding header would still be added

D Response body would be compressed but header missing

💡 Hint

Refer to step 2 where gzip setting is checked to decide compression.

Concept Snapshot

Nginx gzip compression:
- Enable with 'gzip on;'
- Specify types with 'gzip_types'
- Compresses matching responses
- Adds 'Content-Encoding: gzip' header
- Saves bandwidth and speeds up delivery

Full Transcript

This visual execution shows how nginx handles gzip compression. When a client sends a request, nginx checks if gzip is enabled. If yes, it checks if the response content type matches the configured gzip_types. If both conditions are true, nginx compresses the response body using gzip and adds the 'Content-Encoding: gzip' header. Then it sends the compressed response to the client. Variables like gzip status, content type, and response compression state change step-by-step. Key moments clarify why only some responses are compressed and the role of the header. The quiz tests understanding of when compression happens and variable states.