Chapter 7 Load Balancing, Failover, and Component Availability

High availability

High availability provides access to your business components and services even if a server is unavailable.

You can use clusters to achieve high availability if:

Each cluster has at least two member servers.
Partitioning is used, and each partition has at least two member servers.
Each cluster has at least two name servers (which either can be members of the cluster or can be external to the cluster).

To guarantee end-to-end high availability, clients should use URLs of the form "iiop://host1:9000;iiop://host2:9000;..." when doing any of the activities listed below.

In the first three cases, the client's URL list should be the cluster's server list, or a subset of that list.

Setting the location property for the PowerBuilder connection object.
Setting the URL for the creation of a SessionManager::Manager object (for C++ and Java CORBA clients).
Setting the InitialContext Provider URL property for Java clients using JNDI.
Setting the NameServiceURL during ORB initialization. In this case, the client's URL list should be the cluster's name server list, or a subset of the list.

This ensures that no part of a client's initialization is limited to a single point of failure.

You can support non-EAServer clients (that do not support the EAServer-proprietary multiple URL form) by creating an EAServer service component that, upon server start-up, writes a file containing the stringified IOR for a multiserver URL. This IOR file can then be read by any client using an HTTP connection.