Volume Considerations

In many situations, a single Message Broker is sufficient to handle the message processing of one or more MPX-enabled server configurations, depending on the average update volume of your environment.

In environments with a low to moderate number of updates (up to a few thousand updates per hour), the Message Broker can be installed on the same computer as the StarTeam Server. In this case, the Message Broker can handle the message broadcasting for MPX-enabled server configurations on the same computer, as well as for configurations operating on other computers located on the same local area network.

In moderate to high volume update environments (several thousands of updates per hour or more), you should consider operating the Message Broker on a separate computer from the StarTeam Server. This will offload CPU and network demand from the computer hosting the StarTeam Server configuration, providing an opportunity for additional distributed processing.

In some cases, you should consider installing multiple Message Brokers, each on their own computer, and connecting them together into a cloud of Message Brokers. The common scenarios in which multiple Message Brokers are advantageous are listed below.

Large number of simultaneous users	In the ActiveMQ MPX architecture, each subscriber using a unicast connection profile creates a TCP/IP connection to a Message Broker. The MPX Event Transmitter and MPX File Transmitter create additional TCP/IP connections. A single Message Broker can support between 500 and 1,000 simultaneous connections, depending upon message load. The Message Broker has a default limit of 2,000 simultaneous connections and will refuse new connection requests beyond that number. You can increase the maximum connection limit above 2,000, however, in high-volume environments, the Message Broker may not be able to adequately service all connections. In this case, you should consider installing multiple Message Brokers.
Fault-Tolerant / Load Balancing Operation	Multiple Message Brokers can be installed on separate computers and operate in parallel as “peers”. The transmitters can subsequently be configured to randomly choose one Message Broker but, if it is not available, to use a second Message Broker (or a third, and so forth).
Wide Area Networks (WANs)	If the network topology on which your application community operates contains multiple subnets or if the subnets are geographically distributed, you may want to install a Message Broker to serve each “local” user community and connect the Message Brokers into a cloud. This reduces message traffic over the greater network, because messages are transferred between Message Brokers only once, and then replicated locally to directly-attached subscribers.
External Users	If you have users who need to access a StarTeam Server configuration over the public Internet, you may wish to operate a Message Broker that is inside the “DMZ” or completely outside of your corporate firewall. Such a Message Broker would then be connected to other internal Message Brokers, providing external users with ActiveMQ MPX functionality.