Configuring HTTP/2

Configuring HTTP/2
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Enabling the HTTP/2 module in the Jetty server does not create a HTTP/2 specific connector, but rather it adds a HTTP/2 Connection factory to an existing connector. Thus configuring HTTP/2 is a combination of configuring common properties on the connector and HTTP/2 specific properties on the connection factory. The modules and XML files involved can be seen with the following commands:

$ java -jar $JETTY_HOME/start.jar --list-modules
    ...
    1) protonego-boot  <transitive>
    ...
    2) http            ${jetty.base}/start.d/http.ini
    2) ssl             ${jetty.base}/start.d/ssl.ini
    3) alpn            ${jetty.base}/start.d/alpn.ini
    3) http2c          ${jetty.base}/start.d/http2c.ini
    ...
    4) http2           ${jetty.base}/start.d/http2.ini
    5) https           ${jetty.base}/start.d/https.ini

$ java -jar $JETTY_HOME/start.jar --list-config
 ...
 ${jetty.home}/etc/jetty-ssl.xml
 ${jetty.home}/etc/jetty-ssl-context.xml
 ${jetty.home}/etc/jetty-alpn.xml
 ${jetty.home}/etc/jetty-http2c.xml
 ${jetty.home}/etc/jetty-http.xml
 ...
 ${jetty.home}/etc/jetty-http2.xml
 ${jetty.home}/etc/jetty-https.xml

The common properties associated with connectors (host,port, timeouts, etc.) can be set in the module ini files (or start.ini if --add-to-start was used): ${jetty.base}/start.d/http.ini and ${jetty.base}/start.d/ssl.ini. These properties are instantiated in the associated XML files: ${jetty.home}/etc/jetty-http.xml; ${jetty.home}/etc/jetty-ssl.xml, plus the SSL keystore is instantiated in ${jetty.home}/etc/jetty-ssl-context.xml.

Note
If you are planning to edit XML files, make sure to copy them to your {$jetty.base}/etc/ directory before doing so. The XML files that come with the Jetty distribution should not be modified directly.

HTTP/2 specific properties can be set in the module ini files: ${jetty.base}/start.d/http2.ini and ${jetty.base}/start.d/http2c.ini, which are instantiated in the associated XML files: ${jetty.home}/etc/jetty-http2.xml; ${jetty.home}/etc/jetty-http2c.xml, respectively. Currently there are very few HTTP/2 configuration properties and the default values are reasonable:

Table 16.1. HTTP/2 Configuration Properties

Property	Description
jetty.http2.maxConcurrentStreams	The maximum number of concurrently open streams allowed on a single HTTP/2 connection (default 1024). Larger values increase parallelism but cost a memory commitment.
jetty.http2.initialStreamRecvWindow	The initial receive flow control window size for a new stream (default 65535). Larger values may allow greater throughput but also risk head of line blocking if TCP/IP flow control is triggered.