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Caveats, Limitations, and Things to Avoid

Redundant Paths

The current implementation of federation in the M4 broker imposes constraints on redundancy in the topology. If there are parallel paths from a producer to a consumer, multiple copies of messages may be received.

A future release of Qpid will solve this problem by allowing redundant paths with cost metrics. This will allow the deployment of networks that are tolerant of connection or broker loss.

Lack of Flow Control

M4 broker federation uses unlimited flow control on the federation sessions. Flow control back-pressure will not be applied on inter-broker subscriptions.

Lack of Cluster Failover Support

The client functionality embedded in the broker for inter-broker links does not currently support cluster fail-over. This will be added in a subsequent release.

Example Scenarios

Using QPID to bridge disjoint IP networks

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Multi-tiered topology

                        +-----+
                        |  5  |
                        +-----+
                      /         \
              +-----+             +-----+
              |  2  |             |  6  |
              +-----+             +-----+
            /    |    \              |    \
    +-----+   +-----+   +-----+   +-----+   +-----+
    |  1  |   |  3  |   |  4  |   |  7  |   |  8  |
    +-----+   +-----+   +-----+   +-----+   +-----+

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