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[[http2-configuring]]
=== Configuring HTTP/2

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:

[source,shell]
----
$ 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): `${jetty.base}/start.d/http.ini` `${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`.

HTTP/2 specific properties can be set in the module ini files: `${jetty.base}/start.d/http2.ini`; `${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`. 
Currently there are very few HTTP/2 configuration properties and the default values are reasonable:

.HTTP/2 Configuration Properties
[cols=",",options="header",]
|=======================================================================
|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.initialStreamSendWindow |The initial 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.
|=======================================================================
