WebSphere Application Server Dynamic Cluster - Part1

A dynamic cluster is an application server cluster which manages the work loads of cluster members automatically. Dynamic Cluster can expand or contract its cluster members based on the workload. Dynamic Clusters achieves this by using weight and performance information collected from the cluster members.

Dynamic Cluster - A Step by Step Guide
Below are the step by step guide for creating and verifying a Dynamic Cluster in WebSphere Application Server V9.

Note:- As we are using manual cluster creation method create a static cluster before configuring the Dynamic Cluster. If you need any assistance for creating a static cluster, please refer my previous blog post on this.
Configuring and Managing IBM WebSphere Application Server Cluster – Step by Step
  
Step1

Select "Dynamic Cluster" from WebSphere Application Server Console.

Step2

Click on "New", This will open Dynamic Cluster Wizard

Step3

Select "WebSphere Application Server" from the drop down list and click "Next"

Step4

Select the membership method as "Manually define clusters" and Click "Next"
Note:- Automatically defining cluster members will enable automatic provisioning, Details of it be discussed in a different blog post.
  
Step5

Select already created cluster from the drop down list and click "Next"

Step6

You will get above wizard to specify dynamic cluster properties. Most of them are self explanatory but let me try to throw some light here.

Minimum number of cluster instances

* If other dynamic clusters need resources, stop all instances of this cluster during periods of inactivity 

If this option is selected, When other Dynamic Cluster need resources, It enables the Dynamic Cluster manager to free up the resources of these cluster members by stopping all the instances.

Time to wait before stopping instances:

This specifies the wait time in minutes before stopping the instances 

Keep one instance started at all times

This enables to keep one instance up and running always.

Keep multiple instances started at all times

Here you can specify the number of instances to be up and running.

Maximum number of cluster instances

Limit the number of instances that can start

This specifies the maximum number of instances which can be started at a given point of time. ie. Any started instances above this value will be stopped automatically. 

Do not limit the number of instances that can start

This allows unlimited instances to be started. But ensure you have enough resources to accommodate the requirements.

Isolation preference

No isolation requirements 

This option specifies that the members don't have any isolation requirements.

 

Strict isolation 

This specifies the cluster member must be the only running process when started

Associate with isolation group

 Here you can specify an isolation group, members of that group can share the node.

 

Step7

Select the above two options for current scenario.

Step8

This show you the description of selected options.
Click on "Finish"

Step9

As I created a two member cluster before initiating the Dynamic Cluster configuration you can see that the Dynamic Cluster is created with two cluster members. 


Dynamic Cluster - Verification

Step1

 

If you check the above drop down list you will notice three values.
Currently the value is manual.

Manual :- This is as good as a static cluster.
Supervised:- Here you will get recommendations, you can either approve or reject the recommendations.
Automatic:- This option enables the intelligent management to take actions including provisioning requirements automatically.


Step2

Select "Automatic" from drop down list and press "Set Mode"

Step3

 

You can notice that the value got changed to "Automatic" instead of manual.
Click on the Cluster Name link, you will get below page.

Step4

Select above two options. It will ensure one instance is always up and running where as second option limit the number of instances to one.
i.e it will not allow more than one instances of that cluster to be up and running simultaneously.


Step5

Click on "Dynamic Cluster Memeber" Link to see the status of cluster member.

Step6

You can notice from above figure that only one cluster member is up and the other one is down.

Step7

Now let us try to stop the running cluster member to test our dynamic cluster configuration.
Assumption is :- Intelligent management should ensure at least one cluster member to be up and running even if we stop all the members.
Note:- The starting/stopping will take some time, so you need to wait to get the actual status.

Step7

Note that the other cluster member got started automatically.
Here you can notice that even though the second cluster member was stopped earlier, Stopping first cluster member started the second cluster member automatically. It need not be the other (second) member always, Based on various factors intelligent management decides which member to be started.

Now it is your turn .....
I am giving you a scenario to test by yourself.
Please perform below test and record the results in comment.
Start the first (stopped) cluster member and wait for intelligent manager to take action. Observe the cluster member status. Analyze the status and let me know which configuration is enabling it.