All of mod_spdy's configuration options begin with the prefix "Spdy", and most of them can be used either at the top level or within a <VirtualHost> context.

Turning the module on and off

Enabling the module

Once mod_spdy is installed, you must enable it by adding the following directive to your Apache configuration: SpdyEnabled on This will cause your server to advertise SPDY support to clients, and to use SPDY when connecting with SPDY-enabled browsers (such as Chrome, or recent versions of Firefox) over SSL connections.

Note that mod_spdy is still a "beta", and for the time being it is off by default when installed, unless you explicitly enable it with a SpdyEnabled directive. Once the module is more stable, we may change it to being on by default once installed.

Disabling the module

To turn mod_spdy off completely, use: SpdyEnabled off When disabled, mod_spdy will do nothing at all; in particular, it will not spawn its thread pool, serve requests via SPDY, or advertise SPDY support to clients.

Tuning the module

Changing the size of the thread pool

To tune the size of the thread pool mod_spdy uses for processing concurrent SPDY streams, use the directive: SpdyMaxThreadsPerProcess n where n is the number of threads to use on each child process. Note that if you are using a threaded MPM, this thread pool will be shared by all connections on each process. At the moment, the default value is 5 (rather conservative), but this will likely change as we do more performance testing. This directive is valid only at the top level (not within a <VirtualHost> directive).

Changing the limit on simultaneous streams

The SPDY protocol allows endpoints to limit the number of simultanoues SPDY streams they are willing to have open at a time on one connection, for example to limit memory consumption. To set the limit used by mod_spdy, use the directive: SpdyMaxStreamsPerConnection n where n is the maximum number of SPDY streams (i.e. requests) that can be active at any given time on a single connection. It is recommended to keep this limit reasonably high; the current default value is 100.

Changing Sever Push Limits

The SPDY protocol supports server-initiated content push. By default in mod_spdy, only the initial client-initiated request can push content; pushed content can not result in further pushed content, because this could potentially result in unwanted extra content in the best case and infinite recursion in the worst. However, you can adjust this restriction with the directive: SpdyMaxServerPushDepth n where n is the maximum distance from the initial client request that a push can be initiated. A push depth of 1, the default, allows only the initially requested content to push more content. A push depth of 2 will allow that pushed content to result in more pushes. Setting this value to 0 effectively turns off server push. Note that recursive server push is currently allowed and should be watched for if you set this value to a high number: a.html could push b.html which can in turn push a.html again which would push b.html, etc.

Debugging

mod_spdy has several config options useful for debugging the module, which begin with the prefix "SpdyDebug". It is not recommended to use these options in production.

Enabling more verbose logging

To enable more verbose logging output from mod_spdy, beyond what is normally logged at LogLevel debug, use: SpdyDebugLoggingVerbosity n where n is a non-negative integer. Zero is the default, and does not enable any new logging; 5 will enable many additional log messages. Note that this directive will have no effect unless Apache's LogLevel is set to debug. This directive is valid only at the top level (not within a <VirtualHost> directive).

Debugging SPDY without SSL

Normally SPDY is only ever used for SSL connections (https URLs). To tell mod_spdy to use SPDY even for non-SSL connections (http URLs), use: SpdyDebugUseSpdyForNonSslConnections n where n is the SPDY version to use (either 2 or 3). Note that this will break http URLs for browsers, so never use it in production. It can be useful, for example, if you want to debug the SPDY connection with a tool such as Wireshark without having to deal with encryption. Running Chrome with the --use-spdy=no-ssl flag will allow Chrome to talk to mod_spdy in this mode. This option is off by default; you can explicitly disable it with SpdyDebugUseSpdyForNonSslConnections off.