Introduction

Knox 0.14.0 includes a number of new features involving/supporting dynamic configuration.

• Simple Topology Descriptors for Topology Generation and Deployment
• Cluster service endpoint URL discovery
• Ambari Cluster Monitoring
• ZooKeeper Configuration Monitoring
  
  

This article assumes the existence of an Ambari(2.6+)-managed Hadoop cluster, and a ZooKeeper (part of the cluster, or any other). The HDP sandbox is sufficient.

This article will walk through (at a high level):

• The configuration of Knox to support these new features
• The creation of a basic provider configuration and simple descriptor
• The deployment of this descriptor (including service URL discovery)
• The use of the Admin API for managing simple descriptors and provider configurations
• The monitoring of, and response to, cluster configuration changes.
• Provider configuration and descriptors hosted in ZooKeeper
• The Knox CLI additions for managing these resources in ZooKeeper

Ambari Configuration

This step can be skipped for the HDP Sandbox, where the user maria_dev has adequate permissions.

Otherwise, create a user with the Cluster User role in Ambari (e.g., discovery). The Cluster User role can view information about the cluster and its services,
including configurations, service status, and health alerts.
This user will be employed by Knox for discovering service configuration details for a cluster, without having administrator privileges.

Gateway Configuration

The gateway interacts with the Ambari API to get details about clusters. For this purpose, credentials are required, and aliases are used primarily for passwords.

The default aliases used are:

For this example, define the ambari.discovery.password alias for the Knox instance prior to any attempt to deploy a simple descriptor.

{GATEWAY_HOME}/bin/knoxcli.sh create-alias ambari.discovery.password --value discoverysecret (for maria_dev user, this value is maria_dev)

Don't worry about the username now, since it will be explicitly specified in the descriptor you deploy.

Ambari Cluster Monitoring

Knox is capable of monitoring Ambari-managed clusters, from which it has generated topologies, for configuration changes.

By default, this monitor is disabled. To enable it, the value of the following property in gateway-site.xml must be true.

<property>
    <name>gateway.cluster.config.monitor.ambari.enabled</name>
    <value>true</value>
    <description>Enable/disable Ambari cluster configuration monitoring.</description>
</property>

If this monitor is enabled, the value of the following property will determine the frequency with which it will check the Ambari configuration for changes.

<property>
    <name>gateway.cluster.config.monitor.ambari.interval</name>
    <value>30</value>
    <description>The interval (in seconds) for polling Ambari for cluster configuration changes.</description>
</property>

ZooKeeper Configuration Monitoring

Knox is capable of monitoring Apache ZooKeeper for provider configurations and descriptors. To enable this, the following properties must be defined in gateway-site.xml.
(N.B., The address component of the gateway.remote.config.registry.sandbox-zookeeper-client property value must correspond to the ZooKeeper being used.)

<property>
    <name>gateway.remote.config.registry.sandbox-zookeeper-client</name>
    <value>type=ZooKeeper;address=localhost:2181</value>
    <description>ZooKeeper configuration registry client.</description>
</property>

<property>
    <name>gateway.remote.config.monitor.client</name>
    <value>sandbox-zookeeper-client</value>
    <description>Remote configuration monitor client name.</description>
</property>

Start the Gateway

If it's not already running, start the demo LDAP server: {GATEWAY_HOME}/bin/ldap.sh start

Start the gateway with the aforementioned configuration changes: {GATEWAY_HOME}/bin/gateway.sh start

Create a Provider Configuration

Provider configurations are externalized from topology descriptors to promote sharing across topologies. Their content is exactly what you would find in any topology XML prior to this release.

Create sandbox-providers.xml with the follwing content:

<gateway>
    <provider>
        <role>authentication</role>
        <name>ShiroProvider</name>
        <enabled>true</enabled>
        <param name="sessionTimeout" value="30"/>
        <param name="main.ldapRealm" value="org.apache.hadoop.gateway.shirorealm.KnoxLdapRealm"/>
        <param name="main.ldapContextFactory" value="org.apache.hadoop.gateway.shirorealm.KnoxLdapContextFactory"/>
        <param name="main.ldapRealm.contextFactory" value="$ldapContextFactory"/>
        <param name="main.ldapRealm.userDnTemplate" value="uid={0},ou=people,dc=hadoop,dc=apache,dc=org"/>
        <param name="main.ldapRealm.contextFactory.url" value="ldap://localhost:33389"/>
        <param name="main.ldapRealm.contextFactory.authenticationMechanism" value="simple"/>
        <param name="urls./**" value="authcBasic"/>
    </provider>
</gateway>

Create a Simple Descriptor

Simple descriptors, as the name implies, are intended to simplify the declaration of which services should be included in a topology. By including a few discovery details, Knox can determine the endpoint URLs for the declared services.
The endpoint URLs can still be specified in these descriptors, for instance, if Ambari is not managing the target cluster or you need to override the endpoint for some reason.

Create discovery-sandbox.json with the following content:

In this descriptor, the discovery-user property value needs to match the Ambari user with at least Cluster User permissions. For this example, it is either maria_dev (for the HDP sandbox) or whatever user
you've defined for this purpose (see Ambari Configuration).

{
  "discovery-address":"http://localhost:8080",
  "discovery-user":"discovery",
  "provider-config-ref":"sandbox-providers",
  "cluster":"Sandbox",
  "services":[
    {"name":"NAMENODE"},
    {"name":"JOBTRACKER"},
    {"name":"WEBHDFS"},
    {"name":"WEBHCAT"},
    {"name":"OOZIE"},
    {"name":"WEBHBASE"},
    {"name":"RESOURCEMANAGER"}
  ]
}

Deploy the Configuration

These configuration files need to be deployed to the Knox instance, which will result in the generation and deployment of the discovery-sandbox.xml topology.
There are multiple means to accomplish this, including simple file copies (if you have access to the gateway host filesystem) and the Admin API.

File Copy

If you have access to the Knox host filesystem, you can simply copy the provider configuration and simple descriptor to the {GATEWAY_HOME}/conf/shared-providers and {GATEWAY_HOME}/conf/descriptors directories respectively.
For obvious reasons, it's important to deploy the provider configuration before any referencing descriptors.

cp sandbox-providers.xml {GATEWAY_HOME}/conf/shared-providers/
cp discovery-sandbox.json {GATEWAY_HOME}/conf/descriptors/

Admin API

Alternatively, the Knox Admin API can be used to deploy the configuration files

Replace these placeholders in the following URLs: {gateway-host} (e.g., localhost), {gateway-port} (e.g., 8443), {gateway-path} (e.g., gateway)

Deploy the Provider Configuration

curl -iku admin:admin-password https://{gateway-host}:{gateway-port}/{gateway-path}/admin/api/v1/providerconfig/sandbox-providers \
     -X PUT \ 
     -H Content-Type:application/xml \
     -d "@sandbox-providers.xml"

Deploy the Descriptor

curl -iku admin:admin-password https://{gateway-host}:{gateway-port}/{gateway-path}/admin/api/v1/descriptors/discovery-sandbox \
     -X PUT \
     -H Content-Type:application/json \
     -d "@discovery-sandbox.json"

Following either method of deployment, review the resulting topology file, discovery-sandbox.xml, and you'll find that it's a normal Knox topology, with all of the service URLs populated according to the cluster being proxied.

Ambari Cluster Monitoring

Knox is capable of monitoring Ambari instances, from which it has previously discovered cluster details, to identify changes that affect deployed topologies.

When the monitor discovers changes, it will trigger regeneration of the affected deployed topologies based on the changes, and redeploy the same.

Try It

To see this in action, try modifying a configuration property for a service in your cluster:

1. Navigate in Ambari to the Advanced yarn-site config, change the yarn.http.policy value to HTTPS_ONLY, and save the configuration.
2. Watch {GATEWAY_HOME}/logs/gateway.log for messages about noticing a cluster configuration change and regeneration/redeployment of the associated topology.
3. View the contents of the updated corresponding topology in {GATEWAY_HOME}/conf/topologies/, and note that the RESOURCEMANAGER URL now has an https scheme and a different port.
4. In Ambari, change the property value back to HTTP_ONLY, and note the subsequent update of the RESOURCEMANAGER URL in the re-generated topology.
   
   

ZooKeeper Configuration Monitoring

We've seen two means for deploying provider configurations and simple descriptors to a Knox instance: The host filesystem and the Admin API.

Knox is also capable of monitoring Apache ZooKeeper for the addition/modification/removal of provider configurations and simple topology descriptors, and effecting gateway changes as a result.

When a provider configuration is added or modified under the monitored /knox/config/shared-providers znode, every Knox instance that is monitoring this znode will download the new file to its local {GATEWAY_HOME}/conf/shared-providers directory. Note that updates to a provider configuration will result in updates to every generated topology that references it.

When a descriptor is added or modified under the monitored /knox/config/descriptors znode, every Knox instance that is monitoring this znode will download the new file to its local {GATEWAY_HOME}/conf/descriptors directory, and attempt to generate a toploogy based on its contents.

Removals from these znodes are treated similarly, in that they result in the removal of the corresponding local files. When a descriptor is removed, it results in the undeployment of the corresponding topology.

KnoxCLI Support for Configuration in ZooKeeper

The Knox CLI provides some commands to faciliate easier management of these configuration files in ZooKeeper:

Try It

Invoke the Knox CLI commands to upload the configuration files you've created to ZooKeeper:

      {GATEWAY_HOME}/bin/knoxcli.sh upload-provider-config sandbox-providers.xml --registry-client sandbox-zookeeper-client --entry-name alt-providers.xml

      {GATEWAY_HOME}/bin/knoxcli.sh upload-descriptor discovery-sandbox.json --registry-client sandbox-zookeeper-client --entry-name sandbox-copy.json

Knox will notice these additions, and the result will be sandbox-copy.xml in {GATEWAY_HOME}/conf/topologies.

Repeat the Ambari cluster configuration change test, and notice that both discovery-sandbox.xml and sandbox-copy.xml are regenerated and redeployed with updated RESOURCEMANAGER URLs.

Effect Policy Change Across Multiple Topologies

Add the hostmap provider to the local copy of sandbox-providers.xml you created earlier:

<gateway>
    <provider>
        <role>authentication</role>
        <name>ShiroProvider</name>
        <enabled>true</enabled>
        <param name="sessionTimeout" value="30"/>
        <param name="main.ldapRealm" value="org.apache.hadoop.gateway.shirorealm.KnoxLdapRealm"/>
        <param name="main.ldapContextFactory" value="org.apache.hadoop.gateway.shirorealm.KnoxLdapContextFactory"/>
        <param name="main.ldapRealm.contextFactory" value="$ldapContextFactory"/>
        <param name="main.ldapRealm.userDnTemplate" value="uid={0},ou=people,dc=hadoop,dc=apache,dc=org"/>
        <param name="main.ldapRealm.contextFactory.url" value="ldap://localhost:33389"/>
        <param name="main.ldapRealm.contextFactory.authenticationMechanism" value="simple"/>
        <param name="urls./**" value="authcBasic"/>
    </provider>
    <provider>
        <role>hostmap</role>
        <name>static</name>
        <enabled>true</enabled>
        <param name="localhost" value="sandbox,sandbox.hortonworks.com"/>
    </provider>
</gateway>

And replace the sandbox-providers.xml configuration in ZooKeeper with this updated version:

{GATEWAY_HOME}/bin/knoxcli.sh upload-provider-config sandbox-providers.xml --registry-client sandbox-zookeeper-client

Undeploy a Topology by Removing Its Corresponding Descriptor

Delete the descriptor from ZooKeeper, and the corresponding topology will be undeployed from the Knox instance:

{GATEWAY_HOME}/bin/knoxcli.sh delete-descriptor sandbox-copy.json --registry-client sandbox-zookeeper-client

Remove a Provider Configuration

Delete the provider configuration from ZooKeeper, and the corresponding file will be removed from the Knox istance.

{GATEWAY_HOME}/bin/knoxcli.sh delete-provider-config alt-providers.xml --registry-client sandbox-zookeeper-client

Summary

With these features, Knox has become easier to use. Administrators no longer need to track down all the service URLs for each and every toplogy they deploy. It's now possible to effect
policy changes for multiple topologies across multiple Knox instances with a single file change in one location. Knox has also gained the ability to dynamically respond to cluster changes.

The User Guide has more details about these new features.