Dynamic Clusters
Let’s take a look at some of the possibilities as we create a dynamic cluster.
I have created a VMWare
environment.
We have environment consists of four VM’s with the following specs.
- 2 vCPU’s
- 4 Gb memory
- 50 Gb disk
- Oracle Linux 6.6
- Java 1.7.0_75
- Weblogic 12.1.3.0.2
I created a simple domain called base_domain with only an AdminServer and four machines.
After unpacking the domain to the four servers, the nodemanagers where
started and are reachable by the AdminServer.
let go through the process of creating a dynamic cluster.
Open the Weblogic Console and
navigate to Environment -> Clusters
Lock and Edit the domain in the Change Center
note. I make it a good practice always creating a domain in production mode,
even in Development and Test.
Create a new dynamic cluster
New -> Dynamic Cluster
Provide the Clustername
Cluster name: dyna-cluster
Click Next
We will start of with a cluster containing two dynamic servers.
Number of Synamic Servers: 2
Server Name Prefix: dyna-server-
Click Next
For this demo all machines will take part.
Select ‘Use any machine configured
in this domain’
Click Next
Assign each dynamic server unique listen ports
Listen Port for First Server: 8000
SSL Listen Port for First Server: 9000
Click Next
Summary screen
Click Finish
With the creation of the Dynamic Cluster there is also a Server Template created for it.
Server templates
A single server template provides
the basis for the creation of the dynamic servers. Using this single template
provides the possibility of every member being created with exactly the same
attributes. Where some of the server-specific attributes like Servername,
listen-ports, machines, etc. can be calculated based upon tokens.
You can pre-create server templates and let Weblogic clone one when a Dynamic
Cluster is created.
When none is available a server template is create with the Dynamic Cluster.
The name and the listen ports are the only server template attributes that you
provide during Dynamic Cluster creation.
Before we activate the changes to
the domain, we are going to make a change to the server template.
As an example we are going to demonstrate the use of tokens for server-specific
configuration.
Navigate to Environment -> Clusters -> Server Templates
Click on the name: dyna-server-Template
We are going to use the ${ID} token in the Listen Address
Listen Address: 192.168.100.4${ID}
Click Save
The last digit of the listen address is used to make the listen address dynamic.
Activate changes in the Change
Center of the Weblogic Console.
After activation the cluster and two managed servers are created.
We can now start the two servers.
In the previous steps we have added a dynamic cluster with two dynamic servers, based on a single server template, to the domain.
Scaling a Dynamic Cluster
When the capacity is insufficient
and you need to scale-up, you can add dynamic servers on demand.
It requires only a few clicks.
Navigate to Environment -> Clusters
Click dyna-cluster
On the Configuration tab go to the Servers tab
Change the Maximum Number of Dynamic
Servers to: 4
Click save
Activate changes in the Change
Center of the Weblogic Console.
After activation two Dynamic Servers are added to the Dynamic Cluster.
Start the two new Dynamic Servers and you have doubled you capacity.
Scaling down works exactly the same.
Just lower the Maximum Number of DynamicServers and activate.
A few points to keep in mind when scaling up or down.
Up
- New dynamic servers are not started upon creation
- Think before you act with the use of Tokens.
For example.
In our demo, the number of Dynamic servers can’t grow beyond nine servers, since we use the ${ID} as last digit of the listen address.
Down
- Dynamic Servers above the new Maximum have to be shutdown before the change can be activated.
- Dynamic Servers are removed in order, Last -> First
(In our demo dyna-server-4 gets removed first, then dyna-server-3, etc..) - You cannot remove a Dynamic Server directly from the Environment -> Servers page
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