Support for Failover and Load Balancing
The UnboundID LDAP SDK for Java provides a mechanism that can be used to manage
connections across multiple servers. This can be used to provide basic support
for failover and load balancing, and it can be used for single connections as well
as connection pools (so a single connection pool may contain connections to
multiple servers, effectively balancing the load across those servers).
The abstract ServerSet class defines the basic API used to provide this
functionality. At present, the following implementations are available:
-
A single server set, which contains a reference to a single server. It is
primarily used for cases in which a server set may be needed, but only a single
server is to be used.
-
A fewest connections server set, in which each subsequent connection will be
established to the server with the smallest number of established connections.
If a given server isn't available, then it wil be skipped and the server with
the next fewest connections will be used instead.
-
A round robin server set, in which each subsequent connection will be established
to the next server in the specified list. If a given server isn't available,
then it will be skipped and the server set will move to the next server in the
list.
-
A failover server set, in which all attempts to create a connection will be tried
against the first server in the list, and will only try the second if the first
is unavailable, and only try the third if both the first and second are
unavailable, etc.
-
A fastest connect server set, in which the LDAP SDK will attempt to create
connections to multiple servers concurrently and will use the first one to be
established.
-
A round robin DNS server set, which can handle cases in which a single DNS name
is associated with multiple IP addresses.
-
A DNS SRV record server set, in which the set of available directory servers can
be discovered from DNS through SRV records.
Note that the failover server set can also provide failover across server sets, so
it is possible to define more complex configurations (e.g., if possible, use
round-robin load balancing across servers in the local data center, but if none of
them are available then fail over to a round-robin set of servers in a remote data
center).
The server set API is extensible, and developers are free to create their own
implementations if none of the existing options is ideal for a given deployment.
