Chapter 3. Define Cluster Topology

The Knox Gateway supports one or more Hadoop clusters. Each Hadoop cluster configuration is defined in a topology deployment descriptor file in the /etc/knox/conf/topologies directory and is deployed to a corresponding WAR file in the /var/lib/knox/data/deployments directory. These files define how the gateway communicates with each Hadoop clusters.

The descriptor is an XML file contains the following sections:

gateway/provider: Configuration settings enforced by the Knox Gateway while providing access to the Hadoop cluster.
service: Defines the Hadoop service URLs used by the gateway to proxy communications from external clients.

The following table provides an overview of the providers and services:

Table 3.1. Cluster Topology Provider and Service Roles

Type	Role	Description
gateway/provider	hostmap	Maps external to internal node hostnames, replacing the internal hostname with mapped external name when hostname is embedded in a response from the cluster, see Map Hadoop Cluster Host Names.
	authentication	Integrates an LDAP store to authenticate external requests accessing the cluster via the Knox Gateway, see Set up LDAP Authentication.
	federation	Defines HTTP header authentication fields for an SSO or federation solution provider, see Set up HTTP Header Authentication for Federation/SSO.
	identity-assertion	Maps external authenticated users to an internal cluster user that the gateway asserts as the current session user or group, see Configure Identity Assertion.
	authorization	Service level authorization that restricts cluster access to specified users, groups and/or IP addresses, see Configure Service Level Authorization.
	webappsec	Configures a web application security plug-in that provides protection filtering against Cross Site Request Forgery attacks, see Configure Web Application Security.
service	`$service_name`	Binds a Hadoop service with an internal URL that the gateway uses to proxy requests from external clients to the internal cluster services, see Configure Hadoop Service URLs.

	Note
	The gateway automatically redeploys the cluster when a new topology descriptor file or change is detected.

Cluster topology descriptors have the following XML format:

<topology>
   <gateway>
     <provider>
        <role></role>
        <name></name>
        <enabled></enabled>
        <param>
            <name></name>
            <value></value>
        </param>
      </provider>
   </gateway>
   <service>
   </service>
</topology>

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