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Varnish Cache Plus

Brotli

Description

The brotli vmod brings full Brotli compression support to Varnish.

This includes validating Brotli response bodies, compressing bodies before inserting into cache, and on the fly delivery transcoding for clients who do not support Brotli. vmod_brotli can even transcode GZIP into Brotli and vice versa, either on insertion or on delivery. In the case where ESI is used and a Brotli body is returned, vmod_brotli will convert the body to GZIP for better performance since ESI is optimized for GZIP only.

Brotli, developed by Google, is a lossless compressed data format that compresses data using a combination of the LZ77 algorithm and Huffman coding. This is similar to Varnish’s native compression algorithm, GZIP. Brotli compression has shown to have a higher compression ratio compared to the GZIP family of compression algorithms with similar speeds. Brotli is growing in popularity since its inception with support by all major browsers.

Once Brotli support is enabled via the API below, Brotli objects can be inserted into cache and delivered to clients. If your backend supports Brotli natively, init() or accept() can be used to instruct Varnish to accept Brotli objects. When calling init() a global context is created and will allow Brotli to be fetched on all requests. accept() is for per request control on whether to fetch a Brotli object. When both accept() and init() are called at the same time, accept will override the global settings set up in init() with the settings from accept().

compress() and decompress() allow Varnish to perform Brotli operations on the server in sub vcl_backend_response if your backend does not natively support Brotli.

To disable Brotli support completely, add -p http_brotli_support=off to the varnishd start command. Brotli support is default on. When http_gzip_support is off http_brotli_support cannot be enabled.

Examples

Add Brotli support

This is the recommended configuration. This adds Brotli support to Varnish and keeps GZIP support in place. The backend is responsible for the actual Brotli encoding. Clients who do not support Brotli will get a transcoded GZIP response.

import brotli;

sub vcl_init {
  brotli.init(BOTH, transcode = true);
}

Compress response bodies with Brotli

In the case that a backend doesn’t support Brotli but you want to deliver Brotli to clients, you can store all compressible objects as Brotli in cache. Clients who do not support Brotli will get a transcoded GZIP response.

import brotli;

sub vcl_init {
  brotli.init(BOTH, transcode = true);
}

sub vcl_backend_response {
  if (beresp.http.content-encoding ~ "gzip" ||
      beresp.http.content-type ~ "text") {
        brotli.compress();
  }
}

Allow Brotli objects per request

Enable Brotli for certain content types. This does not allow for transcoding. Clients who do not support Brotli will get plaintext. The backend is responsible for Brotli compression.

import brotli;

sub vcl_backend_fetch {
  if (bereq.url ~ "\.(js|css|html)") {
    brotli.accept(BR);
  }
}

Overwriting global settings

import brotli;

sub vcl_init {
  brotli.init(BR, 0.75, 0.5);
}

sub vcl_backend_fetch {
  brotli.accept(BOTH, 0.5, 0.75);
}

Dual Object Support

By default Varnish will only store one content encoding per object: either GZIP or Brotli. It is possible to store both encodings simultaneously, preventing the need for deliver transcoding. Note that this will use more storage in the cache. This can be done by setting the Vary response header to a copy of the Accept-Encoding header (x-ae).

import brotli;

sub vcl_init {
  brotli.init(encoding = BOTH);
}

sub vcl_recv {
  if (req.http.accept-encoding ~ "br") {
    set req.http.x-ae = "br";
  } else {
    set req.http.x-ae = "gzip";
  }
}

sub vcl_backend_response {
  set beresp.http.vary = "x-ae";
}

sub vcl_deliver {
  unset resp.http.vary;
}

API

init

VOID init(ENUM {BR, GZIP, BOTH, NONE} encoding, [REAL br_q = 1], [REAL gzip_q = 1], BYTES buf_size = 32768, ENUM {GENERIC, UTF8, FONT} mode = GENERIC, INT quality = 6, INT window_size = 22, BOOL large_window = 0, BOOL transcode = 0)

Set up global Brotli settings. Can only be called in sub vcl_init.

Note:

br_q and gzip_q are numbers between 0 and 1 with no more than 3 digits after the decimal point. quality is a number between 0 and 11 where 11 is a higher rate of compression. window_size is a value between 10 and 24.

Arguments:

  • br_q accepts type REAL with a default value of 1 optional

  • gzip_q accepts type REAL with a default value of 1 optional

  • buf_size accepts type BYTES with a default value of 32768 optional

  • quality accepts type INT with a default value of 6 optional

  • window_size accepts type INT with a default value of 22 optional

  • large_window accepts type BOOL with a default value of 0 optional

  • transcode accepts type BOOL with a default value of 0 optional

  • encoding is an ENUM that accepts values of BR, GZIP, BOTH, and NONE

  • mode is an ENUM that accepts values of GENERIC, UTF8, and FONT with a default value of GENERIC optional

Type: Function

Returns: None

accept

VOID accept(ENUM {BR, GZIP, BOTH, NONE} encoding, [REAL br_q = 1], [REAL gzip_q = 1])

Set up or change per request Brotli support. This will dictate the type of object (GZIP, Brotli or plain text) that should be in cache. Can only be called in sub vcl_backend_fetch.

Arguments:

  • br_q accepts type REAL with a default value of 1 optional

  • gzip_q accepts type REAL with a default value of 1 optional

  • encoding is an ENUM that accepts values of BR, GZIP, BOTH, and NONE

Type: Function

Returns: None

compress

VOID compress([BYTES buf_size = 32768], [ENUM {GENERIC, UTF8, FONT} mode = GENERIC], [INT quality = 6], [INT window_size = 22], [BOOL large_window = 0])

Use Brotli to compress the response body. Can only be called in sub vcl_backend_response.

Note: quality is a number between 0 and 11 where 11 is a higher rate of compression and window_size is a value between 10 and 24.

Arguments:

  • buf_size accepts type BYTES with a default value of 32768 optional

  • quality accepts type INT with a default value of 6 optional

  • window_size accepts type INT with a default value of 22 optional

  • large_window accepts type BOOL with a default value of 0 optional

  • mode is an ENUM that accepts values of GENERIC, UTF8, and FONT with a default value of GENERIC optional

Type: Function

Returns: None

decompress

VOID decompress([BOOL large_window = 0])

Decompress a Brotli response body. Can only be called in sub vcl_backend_response.

Arguments:

  • large_window accepts type BOOL with a default value of 0 optional

Type: Function

Returns: None

Availability

The brotli VMOD is available in Varnish Cache Plus version 6.0.6r10 and later.