Apache Module mod_brotli

Summary

Themod_brotli module provides theBROTLI_COMPRESS output filter that allows output from your server to be compressed using the brotli compression format before being sent to the client over the network. This module uses the Brotli library found athttps://github.com/google/brotli.

Topics

• Sample Configurations
• Enabling Compression
• Dealing with proxy servers
• Serving pre-compressedcontent

Directives

• BrotliAlterETag
• BrotliCompressionMaxInputBlock
• BrotliCompressionQuality
• BrotliCompressionWindow
• BrotliFilterNote

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• Filters
• Comments

Sample Configurations

This is a simple configuration that compresses common text-based content types.

AddOutputFilterByType BROTLI_COMPRESS text/html text/plain text/xml text/css text/javascript application/javascript

Enabling Compression

Output Compression

Compression is implemented by theBROTLI_COMPRESSfilter. The following directive will enable compression for documents in the container where it is placed:

SetOutputFilter BROTLI_COMPRESSSetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-brotli

If you want to restrict the compression to particular MIME types in general, you may use theAddOutputFilterByType directive. Here is an example of enabling compression only for the html files of the Apache documentation:

<Directory "/your-server-root/manual">    AddOutputFilterByType BROTLI_COMPRESS text/html</Directory>

Dealing with proxy servers

Themod_brotli module sends aVary: Accept-Encoding HTTP response header to alert proxies that a cached response should be sent only to clients that send the appropriateAccept-Encoding request header. This prevents compressed content from being sent to a client that will not understand it.

If you use some special exclusions dependent on, for example, theUser-Agent header, you must manually configure an addition to theVary header to alert proxies of the additional restrictions. For example, in a typical configuration where the addition of theBROTLI_COMPRESS filter depends on theUser-Agent, you should add:

Header append Vary User-Agent

If your decision about compression depends on other information than request headers (e.g. HTTP version), you have to set theVary header to the value*. This prevents compliant proxies from caching entirely.

Header set Vary *

Serving pre-compressedcontent

Sincemod_brotli re-compresses content each time a request is made, some performance benefit can be derived by pre-compressing the content and telling mod_brotli to serve them without re-compressing them. This may be accomplished using a configuration like the following:

<IfModule mod_headers.c>    # Serve brotli compressed CSS files if they exist    # and the client accepts brotli.    RewriteCond "%{HTTP:Accept-encoding}" "br"    RewriteCond "%{REQUEST_FILENAME}\.br" "-s"    RewriteRule "^(.*)\.css"              "$1\.css\.br" [QSA]    # Serve brotli compressed JS files if they exist    # and the client accepts brotli.    RewriteCond "%{HTTP:Accept-encoding}" "br"    RewriteCond "%{REQUEST_FILENAME}\.br" "-s"    RewriteRule "^(.*)\.js"               "$1\.js\.br" [QSA]    # Serve correct content types, and prevent double compression.    RewriteRule "\.css\.br$" "-" [T=text/css,E=no-brotli:1]    RewriteRule "\.js\.br$"  "-" [T=text/javascript,E=no-brotli:1]    <FilesMatch "(\.js\.br|\.css\.br)$">      # Serve correct encoding type.      Header append Content-Encoding br      # Force proxies to cache brotli &      # non-brotli css/js files separately.      Header append Vary Accept-Encoding    </FilesMatch></IfModule>

BrotliAlterETagDirective

TheBrotliAlterETag directive specifies how the ETag hader should be altered when a response is compressed.

AddSuffix

Append the compression method onto the end of the ETag, causing compressed and uncompressed representations to have unique ETags. In another dynamic compression module, mod_deflate, this has been the default since 2.4.0. This setting prevents serving "HTTP Not Modified" (304) responses to conditional requests for compressed content.

NoChange

Don't change the ETag on a compressed response. In another dynamic compression module, mod_deflate, this has been the default prior to 2.4.0. This setting does not satisfy the HTTP/1.1 property that all representations of the same resource have unique ETags.

Remove

Remove the ETag header from compressed responses. This prevents some conditional requests from being possible, but avoids the shortcomings of the preceding options.

BrotliCompressionMaxInputBlockDirective

TheBrotliCompressionMaxInputBlock directive specifies the maximum input block size between 16 and 24, with the caveat that larger block sizes require more memory.

BrotliCompressionQualityDirective

TheBrotliCompressionQuality directive specifies the compression quality (a value between 0 and 11). Higher quality values result in better, but also slower compression.

BrotliCompressionWindowDirective

TheBrotliCompressionWindow directive specifies the brotli sliding compression window size (a value between 10 and 24). Larger window sizes can improve compression quality, but require more memory.

BrotliFilterNoteDirective

TheBrotliFilterNote directive specifies that a note about compression ratios should be attached to the request. The name of the note is the value specified for the directive. You can use that note for statistical purposes by adding the value to youraccess log.

BrotliFilterNote ratioLogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' brotliCustomLog "logs/brotli_log" brotli

If you want to extract more accurate values from your logs, you can use thetype argument to specify the type of data left as a note for logging.type can be one of:

Input

Store the byte count of the filter's input stream in the note.

Output

Store the byte count of the filter's output stream in the note.

Ratio

Store the compression ratio (output/input * 100) in the note. This is the default, if thetype argument is omitted.

Thus you may log it this way:

BrotliFilterNote Input instreamBrotliFilterNote Output outstreamBrotliFilterNote Ratio ratioLogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' brotliCustomLog "logs/brotli_log" brotli

See also

• mod_log_config