Broker networks
We can link brokers together to form a network of brokers. A broker network must be arranged as a hierarchy. The broker at the top of the hierarchy is called the root broker. The root broker can have one or more child brokers, and is known as the parent broker to these brokers. The child brokers can also have child brokers, and so on, as illustrated in Figure 4.
Broker 1 is the root broker and brokers 2 and 3 are its children. Broker 4 is the child of broker 2 and the parent of brokers 7 and 8.
Using a hierarchy reduces the number of channels that need to be defined because each broker does not need to be connected to every other broker. Both publication and subscription traffic take a hierarchic route to their destinations.
Each broker maintains administrative information about its parent broker. When a broker first starts, it communicates with its parent. In this way, each broker knows the identities of its immediate children as well as its parent. These are known as the broker's neighbors.
Define the hierarchy from the root down and, if it is necessary to delete brokers, delete them from the bottom up. This usually means that to change the root broker you have to delete the whole network and start again (in exceptional cases we can use the clrmqbrk command.
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