Server groups

Server groupings enable the user to state that several backend servers are mirrors of each other, and proxy server processing can continue even if one or more backend servers in the group are down, assuming that at least one backend server is online. Connections are restarted periodically if the connections are closed for some reason, such as the remote server is stopped or restarted.

If the proxy server is unable to contact a backend server, or if authentication fails, then proxy server startup fails. The proxy server starts in configuration only mode by default, unless server groupings are defined in the configuration file.

The proxy configuration file supports a special set of entries that enable a directory administrator to define server groups in the configuration file. Each group contains a list of backend servers. As long as at least one backend server in each group can be contacted, the proxy server starts successfully and service client requests, though performance might be degraded. Each backend server in the entry is defined to have an OR relationship, and all the entries have an AND relationship.

The directory administrator must define the server groups by using idsldapadd and idsldapmodify to add and modify the required entries. The directory administrator must ensure that each of the backend servers is placed in a server group and that the backend servers in each server group contain the same partition of the directory database. For example, suppose that server1 and server2 are peers of each other, with server3 and server4 being separate peers, that is, server1 and server2 hold a disjoint data set from server3 and server4.In this case, a user would add server1 and server2 in a server group entry under the cn=configuration suffix, and server3 and server4 in a separate server group entry. If either server1 or server2 is up, then the proxy server can proceed to check if either server3 or server4 is online. If neither server3 or server4 is up, then the proxy server starts in configuration only mode.

In addition to the server grouping, the administrator must add the serverID of each backend server in the server group entry. If the server is down, no root DSE information can be gained, and the serverID is needed for determining the supplier/consumer relationships throughout the topology.

Any backend servers not in a server group that are offline at proxy server startup cause the proxy server to start in configuration only mode.

dn: cn=serverGroup, cn=ProxyDB, cn=Proxy Backends, cn=IBM Directory, cn=Schemas, 
	cn=Configuration
cn: serverGroup
ibm-slapdProxyBackendServerDN: cn=Server1,cn=ProxyDB,cn=Proxy Backends,
	cn=IBM Directory,	cn=Schemas,cn=Configuration
ibm-slapdProxyBackendServerDN: cn=Server2,cn=ProxyDB,cn=Proxy Backends,
	cn=IBM Directory,	cn=Schemas,cn=Configuration
objectclass: top
objectclass: ibm-slapdConfigEntry
objectclass: ibm-slapdProxyBackendServerGroup