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 the BROTLI_COMPRESS filter. The following directive will enable compression for documents in the container where it is placed:

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

If you want to restrict the compression to particular MIME types in general, you may use the AddOutputFilterByType 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

The mod_brotli module sends a Vary: Accept-Encoding HTTP response header to alert proxies that a cached response should be sent only to clients that send the appropriate Accept-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, the User-Agent header, you must manually configure an addition to the Vary header to alert proxies of the additional restrictions. For example, in a typical configuration where the addition of the BROTLI_COMPRESS filter depends on the User-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 the Vary header to the value *. This prevents compliant proxies from caching entirely.

Header set Vary *

Serving pre-compressed content

Since mod_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>

BrotliAlterETag Directive

The BrotliAlterETag 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.

BrotliCompressionMaxInputBlock Directive

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

BrotliCompressionQuality Directive

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

BrotliCompressionWindow Directive

The BrotliCompressionWindow 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.

BrotliFilterNote Directive

The BrotliFilterNote 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 your access log.

BrotliFilterNote ratio

LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' brotli
CustomLog "logs/brotli_log" brotli

If you want to extract more accurate values from your logs, you can use the type 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 the type argument is omitted.

Thus you may log it this way:

BrotliFilterNote Input instream
BrotliFilterNote Output outstream
BrotliFilterNote Ratio ratio

LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' brotli
CustomLog "logs/brotli_log" brotli

See also

• mod_log_config