[jboss-jira] [JBoss JIRA] (AS7-3976) EJB client sometimes does not loadbalance

[jaikiran pai (JIRA)]

    [ https://issues.jboss.org/browse/AS7-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12672537#comment-12672537 ] 

jaikiran pai commented on AS7-3976:
-----------------------------------

Yes, this needs to fixed/improved. Currently the implementation doesn't allow any way to make the initial node selection (from among the available ones) deterministic, if all the nodes can handle the same deployment. I've seen other users asking for this enhancement too. So as a first step I'm going to introduce a way where an node selection implementation can be used if multiple receivers can handle the same deployment. Here's what I've added:

{code}
package org.jboss.ejb.client;

/**
 * A selector which selects and returns a node, from among the passed eligible nodes, that can handle a specific
 * deployment within a EJB client context. Typical usage of {@link DeploymentNodeSelector} involves load balancing
 * calls to multiple nodes which can all handle the same deployment. This allows the application to have a deterministic
 * node selection policy while dealing with multiple nodes with same deployment.
 *
 * @author Jaikiran Pai
 */
public interface DeploymentNodeSelector {

    /**
     * Selects and returns a node from among the <code>eligibleNodes</code> to handle the invocation on a deployment
     * represented by the passed <code>appName</code>, <code>moduleName</code> and <code>distinctName</code> combination.
     * Implementations of this method must <b>not</b> return null or any other node name which isn't in the
     * <code>eligibleNodes</code>
     *
     * @param eligibleNodes The eligible nodes which can handle the deployment. Will not be empty.
     * @param appName       The app name of the deployment
     * @param moduleName    The module name of the deployment
     * @param distinctName  The distinct name of the deployment
     * @return
     */
    String selectNode(final String[] eligibleNodes, final String appName, final String moduleName, final String distinctName);
}
{code}

This will be similar to the existing org.jboss.ejb.client.ClusterNodeSelector which helps in node selection within a cluster (independent of the deployment).

For 1.0.x versions, we'll be using a RandomDeploymentNodeSelector which will randomly return one of the many eligible nodes for the deployment. This will help is (randomly) distributing the invocations to different nodes and will prevent the current issue where the chances of it going to the same node are high.

For 1.1.x we'll add support for configuring a different implementation for this selector (I am not planning to add the configuration for 1.0.x since it will involve adding a new API on the client configuration interface).
                
> EJB client sometimes does not loadbalance
> -----------------------------------------
>
>                 Key: AS7-3976
>                 URL: https://issues.jboss.org/browse/AS7-3976
>             Project: Application Server 7
>          Issue Type: Bug
>          Components: Clustering, EJB
>    Affects Versions: 1.0.3.Final
>            Reporter: Radoslav Husar
>            Assignee: jaikiran pai
>            Priority: Critical
>
> I noticed that with a 2 node cluster, sometimes all sessions are created only on one node.
> Looks like cluster view is not updating properly on the client.
> See https://hudson.qa.jboss.com/hudson/view/EAP6/view/EAP6-Performance-Clustering/job/eap-6x-stress-ejb-repl-sync-ejbremote/29/console-perf20/ for logs.

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