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-*-org-*-
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements. See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership. The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
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# under the License.
* Active/passive cluster implementation
The active-active cluster can be used in an active-passive mode. In
this mode we would like the cluster to be as efficient as a strictly
active-passive implementation.
An active/passive implementation requires a subset of the active/active approach:
- drop Queue ownership and locking
- replicate subset of Cluster interface, don't need to know all message disposition.
Can re-use:
- cluster membership
- new member updates
- store integration
Simpler implementation of broker::Cluster:
- act like distributed MessageStore. Don't need acquisition details.
- can do immediate local enqueue and still guarantee order.
- can use smaller message IDs: just sequence number. Can be implicit.
Extra requirements:
- Exactly one broker hast to take over if primary fails.
- Passive members refuse client connections and redirect to active member.
- On failover, clients keep trying till they find the active member.
** Active/active vs. active passive
Active/active benefits:
- Total # connections: practical 60k limit per node.
- Handle client losing connectivity to one cluster node - can fail over to any.
- Some load sharing: reading from client + multicast only done on direct node.
- Clients can switch to any broker on failover
- Failure affects a subset of the clients, not all the clients.
Active/active drawbacks:
- Co-ordinating message allocation impacts performance.
Active/passive benefits:
- Don't need message allocation strategy, can feed consumers at top speed.
Active/passive drawbacks:
- All clients on one node so a failure affects every client in the system.
- After a failure there is a "reconnect storm" as every client reconnects to the new active node.
- After a failure there may be a period where no broker is active.
- Can't help clients with no connectivity to the active member.
- Clients must find the single active to fail-over.
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