Compress Plugin

This plugin adds compression and decompression options to both origin and cache responses.

Purpose

Not all clients can handle compressed content. Not all origin servers are configured to respond with compressed content when a client says it can accept it. And it’s not always necessary to make two separate requests to an origin, and track two separate cache objects, for the same content - once for a compressed version and another time for an uncompressed version.

This plugin tidies up these problems by transparently compressing or deflating origin responses, as necessary, so that both variants of a response are stored as alternates and the appropriate version is used for client responses, depending on the client’s indication (via an Accept request header) of what it can support.

Additionally, this plugin adds configurability for what types of origin responses will receive this treatment, which will be proxied and cached with default behavior, and which may be explicitly disallowed to cache both compressed and deflated versions (because, for example, the cost of compression is known ahead of time to outweigh the space and bandwidth savings and you wish to avoid Traffic Server even testing for the possibility).

Installation

This plugin is considered stable and is included with Traffic Server by default. There are no special steps necessary for its installation.

Configuration

This plugin can be used as either global plugin or remap plugin. It can be enabled globally for Traffic Server by adding the following to your plugin.config:

compress.so

With no further options, this will enable the following default behavior:

  • Enable caching of both compressed and uncompressed versions of origin responses as alternates.

  • Compress objects with text/* content types for every origin.

  • Don’t hide Accept encoding headers from origin servers (for an offloading reverse proxy).

  • No URLs are disallowed from compression.

  • Disable flush (flush compressed content to client).

  • Only objects greater than 1Kb will be compressed

Alternatively, a configuration may be specified (shown here using the sample configuration provided with the plugin’s source):

compress.so <path-to-plugin>/sample.compress.config

This can be used as remap plugin by pointing to config file in remap rule remap.config:

@plugin=compress.so @pparam=sample.compress.config

The following sections detail the options you may specify in the plugin’s configuration file. Options may be used globally, or may be specified on a per-site basis by preceding them with a [<site>] line, where <site> is the client-facing domain for which the options should apply.

Per site configuration for remap plugin should be ignored.

cache

When set to true, causes Traffic Server to cache both the compressed and uncompressed versions of the content as alternates. When set to false, Traffic Server will cache only the compressed or decompressed variant returned by the origin. Enabled by default.

range-request

When set to true, causes Traffic Server to compress responses to Range Requests. Disabled by default. Setting this to true while setting cache to false leads to delivering corrupted content.

compressible-content-type

Provides a wildcard to match against content types, determining which are to be considered compressible. This defaults to text/*. Takes one Content-Type per line.

compressible-status-code

A comma separated list of response status codes for which to enable compression. Defaults to 200, 206, 304.

minimum-content-length

Minimum Content-Length value sent by the origin server to consider the response compressible. Due to the overhead and latency of compression and decompression, it only makes sense to compress files above a certain size threshold. Compressing files below 150 bytes can actually make them larger. This setting only applies if the response explicitly sends Content-Length. Regardless of this setting, responses with Content-Length: 0 are considered not compressible. Defaults to 1024 bytes.

allow

Provides a wildcard pattern which will be applied to request URLs. Any which match the pattern will be considered compressible, and only deflated versions of the objects will be cached and returned to clients. This may be useful for objects which already have their own compression built-in, to avoid the expense of multiple rounds of compression for trivial gains. If the regex is preceded by ! (for example allow !*/nothere/*), it disables the plugin from those machine URLs.

enabled

When set to true (the default) permits objects to be compressed, and when false effectively disables the plugin in the current context.

flush

Enables (true) or disables (false) flushing of compressed objects to clients. This calls the compression algorithm’s mechanism (Z_SYNC_FLUSH and for gzip and BROTLI_OPERATION_FLUSH for brotli) to send compressed data early.

remove-accept-encoding

When set to true this option causes the plugin to strip the request’s Accept-Encoding header when contacting the origin server. Setting this option to false will leave the header intact if the client provided it.

  • To ease the load on the origins.

  • For when the proxy parses responses, and the resulting compression and decompression is wasteful.

supported-algorithms

Provides the compression algorithms that are supported, a comma separate list of values. This will allow Traffic Server to selectively support gzip, deflate, and brotli (br) compression. The default is gzip. Multiple algorithms can be selected using ‘,’ delimiter, for instance, supported-algorithms deflate,gzip,br. Note that this list must not contain any white-spaces!

Note that if proxy.config.http.normalize_ae is 1, only gzip will be considered, and if it is 2, only br or gzip will be considered.

Examples

To establish global defaults for all site requests passing through Traffic Server, while overriding just a handful for requests to content at www.example.com, you might create a configuration with the following options:

# Set some global options first
cache true
remove-accept-encoding false
compressible-content-type text/*
compressible-content-type application/json
compressible-status-code 200, 206
minimum-content-length 860
flush false

# Now set a configuration for www.example.com
[www.example.com]
cache false
remove-accept-encoding true
allow !/notthis/*.js
allow /this/*.js
flush true

# Allows brotli encoded response from origin but is not capable of brotli compression
[brotli.allowed.com]
enabled true
compressible-content-type text/*
compressible-content-type application/json
flush true
supported-algorithms gzip,deflate

# Supports brotli compression
[brotli.compress.com]
enabled true
compressible-content-type text/*
compressible-content-type application/json
flush true
supported-algorithms br,gzip

# This origin does it all
[bar.example.com]
enabled false

# A reasonable list of content-types that are compressible
compressible-content-type text/*
compressible-content-type *font*
compressible-content-type *javascript
compressible-content-type *json
compressible-content-type *ml;*
compressible-content-type *mpegURL
compressible-content-type *mpegurl
compressible-content-type *otf
compressible-content-type *ttf
compressible-content-type *type
compressible-content-type *xml
compressible-content-type application/eot
compressible-content-type application/pkix-crl
compressible-content-type application/x-httpd-cgi
compressible-content-type application/x-perl
compressible-content-type image/vnd.microsoft.icon
compressible-content-type image/x-icon

Assuming the above options are in a file at /etc/trafficserver/compress.config the plugin would be enabled for Traffic Server in plugin.config as:

compress.so /etc/trafficserver/compress.config

Alternatively, the compress plugin can be used as a remap plugin:

map http://www.example.com http://origin.example.com \
   @plugin=compress.so @pparam=compress.config

$ cat /etc/trafficserver/compress.config
enabled true
cache true
compressible-content-type *xml
supported-algorithms