5. Resilience

Oak LDAP is normally provided by around four IP addresses spread across two or more data centres (look up the DNS record ldap.oak.ox.ac.uk for current details).

In order to take advantage of the resilience offered, clients need to implement these related behaviours:
  • If a node refuses the connection, or if the initial connection fails due to a timeout or any other reason, try connecting to a different node from the pool. Don't give up until all nodes in the pool have been tried
  • If the node you're connected to closes the connection, or the connection breaks or expires for other reasons, open a new connection to a node currently in the pool (taking care to expire any cached DNS responses according to their TTLs), and reissue any incomplete queries

The exact way to achieve this differs from client to client. Clients not implementing the above behaviours will still work properly a lot of the time, but will not exhibit continuous operation when individual nodes become unavailable, for example due to maintenance operations or component failures.

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