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- Why Clustering: http://publib.boulder.ibm.com/html/as400/v4r4/ic2924/info/RZAIGRZAIGA02.HTM
- Why Would Anyone Need a Computer Cluster?: http://obscuredclarity.blogspot.com/2008/10/why-would-anyone-need-computer-cluster.html
WSO2 provides Hazelcast Community Edition as its default clustering engine. For clustering on a secure channel (i.e., secure Hazelcast), you have to use Hazelcast Enterprise and this is a commercial version of Hazelcast. To integrate with Hazelcast Enterprise, there are provisions to provide license key under clustering configurations. Advanced users can fine-tune Hazelcast by creating a <PRODUCT_HOME>/repository/conf/hazelcast.properties file and adding the relevant Hazelcast properties as described in the Hazelcast Advanced Configuration Properties documentation. If you use Hazelcast Enterprise Edition or Hazelcast Management Center, see the Hazelcast documentation for details on configuring those products and also Advanced Configurations and Information for further details.
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| Multicast | WKA | AWS | Kubernetes |
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| All nodes should be in the same subnet | Nodes can be in different networks | Amazon EC2 nodes | Kubernetes pods |
| All nodes should be in the same multicast domain | No multicasting requirement | No multicasting requirement | No multicasting requirement |
| Multicasting should not be blocked | No multicasting requirement | No multicasting requirement | No multicasting requirement |
| No fixed IP addresses or hosts required | At least one well-known IP address or host required | No fixed IP addresses or hosts required | No fixed IP addresses or hosts required |
| Failure of any member does not affect membership discovery | New members can join with some WKA nodes down, but not if all WKA nodes are down | Failure of any member does not affect membership discovery | Failure of any member does not affect membership discovery |
| Does not work on IaaSs such as Amazon EC2 | IaaS-friendly | Works on Amazon EC2 | Works with Kubernetes and OpenShift EnvironmetnsEnvironments |
| No WKA requirement | Requires keepalive, elastic IPs, or some other mechanism for re-mapping IP addresses of WK members in cases of failure | No WKA requirement | No WKA requirement |
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The Well-Known Addresses (WKA) feature is a mechanism that allows cluster members to discover and join a cluster using unicast instead of multicast. WKA is enabled by specifying a small subset of cluster members (referred to as WKA members) that are able to start a cluster. The WKA member starts the cluster and the other members join the cluster through this WKA member. If the WKA member is down, the cluster breaks, and the members will not be able to communicate with each other. The system should have at least two well-known address (WKA) members in order to work correctly and to recover if a single WKA member fails. |
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If you are setting up multiple WSO2 products in a cluster, it is recommended to set up each product on a separate server. For example, WSO2 ESB is used for message mediation, so a considerable amount of processing happens in the ESB. The DSS does data service hosting and has a different architecture layer from the ESB. If you deploy both the ESB and DSS in the same instance/runtime, it can negatively impact the performance of both, and it also makes scaling difficult. However, you can set up hybrid servers (installing selected DSS features on top of the ESB and vice versa) using WSO2 products without the above performance concerns. |
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Deciding how to set up your cluster
When setting up your cluster, you must consider differed approaches that you need to take. You must decide how you want to setup and share your databases, whether to front your cluster with a load balancer, and whether to use sticky sessions. You also need to make a decision on whether to separate worker and manager concerns in the cluster. The following topics provide more details on these and can help you make a more informed decision.
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