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• Defines how the URL matched by the rule will be rewritten.
• The $serviceUrl[WEATHER]} looks up the <service><url> for the <service><role>WEATHER. This is a implemented as rewrite function and is another custom extension point.
• The {path=**} extracts zero or more values for the 'path’ parameter from the matched URL.
• The {**} extracts any “unused” parameters and uses them as query parameters.

Scope

Rewrites rules can be global and local to the service they are defined in. After Apache Knox 0.6.0 all the rewrites rules are local unless they are explicitly defined as global.

To define global rules use the property 'gateway.global.rules.services' in 'gateway-site.xml' that takes a list of services whose rewrite rules are made global. for. e.g.

    <property>
        <name>gateway.global.rules.services</name>
        <value>"NAMENODE","JOBTRACKER", "WEBHDFS", "WEBHCAT", "OOZIE", "WEBHBASE", "HIVE", "RESOURCEMANAGER"</value>
    </property>

Note: Rewrite rules rules for these services "NAMENODE","JOBTRACKER", "WEBHDFS", "WEBHCAT", "OOZIE", "WEBHBASE", "HIVE", "RESOURCEMANAGER" are global by default.

If you want to define a single rule to be scoped inside a global rewrite rules you can do so by using the attribute 'scope' e.g.

    <!-- Limit the scope of this rule just to WEBHDFS service -->
    <rule dir="OUT" scope="WEBHDFS" name="WEBHDFS/webhdfs/outbound" pattern="hdfs://*:*/{path=**}?{**}">
        <rewrite template="{$frontend[url]}/webhdfs/v1/{path=**}?{**}"/>
    </rule>

Direction

Rewrite rules can be applied to inbound (requests going to the Gateway - from browser, curl etc.) or outbound (response going from the Gateway towards browser) requests/responses. The direction is indicated by the "dir" attribute

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