SSE Support

Server-Sent Events Support¶

Introduction¶

Server-Sent Events (SSE) allows a server to push updates to the browser over a single longlived HTTP connection. The media type is test/event-stream.

Configuration¶

Asynchronous behaviour and therefore SSE support is not enabled by default. Modify the gateway.servlet.async.supported property to true in <KNOX-HOME>/conf/gateway-site.xml file.

  <property>
      <name>gateway.servlet.async.supported</name>
      <value>true</value>
      <description>Enable/Disable async support.</description>
  </property>

Service and rewrite rules need the be updated as well. Both Ha and non Ha configurations work.

Example¶

In the following sample configuration we assume that the backend SSE service URL is http://myhost:7435. And gateway.servlet.async.supported property is set to true as shown above.

Rewrite¶

Example code snippet from <KNOX-HOME>/data/services/{myservice}/{version}/rewrite.xml where myservice = sservice and version = 0.1

  <rules>
      <rule dir="IN" name="SSERVICE/sservice/inbound" pattern="*://*:*/**/sservice/*">
        <rewrite template="{$serviceUrl[SSERVICE]}/sse"/>
      </rule>
  </rules>

Service¶

Example code snippet from <KNOX-HOME>/data/services/{myservice}/{version}/service.xml where myservice = sservice and version = 0.1

  <service role="SSERVICE" name="sservice" version="0.1">
    <routes>
      <route path="/sservice/**"></route>
    </routes>
    <dispatch classname="org.apache.knox.gateway.sse.SSEDispatch" ha-classname="org.apache.knox.gateway.ha.dispatch.SSEHaDispatch"/>
  </service>

Topology¶

Finally, update the topology file at <KNOX-HOME>/conf/{topology}.xml with the backend service URL

  <service>
    <role>SSERVICE</role>
    <url>http://myhost:7435</url>
  </service>