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Chapter 2: Installation and Setup
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When different changes are made to one existing item, two outcomes are possible. For example,
assume an item is added and configured on the hub server and is then replicated to the spoke
server. Later, an administrator changes something about the item on the spoke server. Another
administrator then changes something about the item on the hub server. When the replication
task runs, two things may happen.
In a few instances where no conflict occurs, both changes will be incorporated and replicated.
For example, if the hub server’s administrator adds username JaneDoe to the existing userdefined user group Accounting and the spoke server’s administrator adds username JohnDoe to
the Accounting user group, both names will be added and replicated.
In most other instances where the changes are mutually exclusive or some other conflict occurs,
the most recent change will be the only change accepted and replicated. For example, if the
hub server’s administrator associates a unit with the Miami site, and the spoke server’s
administrator associates the same unit with the Chicago site, the change that was made closest
to the time of replication (that is, the most recent change) will be accepted and replicated.
This emphasizes the importance of ensuring the hub and spoke servers’ clocks are synchronized.
The exception to the last-change rule is when one of the actions deletes an item - in that case,
the deletion is accepted and replicated, regardless of timing. For example, if a unit was deleted
on the hub server, and then the contact information for the same unit was changed on the spoke
server a minute later, the unit will be deleted when the replication task is run.
On a spoke server, you may enable a replication task property that forces the spoke server to
retrieve a snapshot of the hub database rather than synchronizing changes back and forth. The
snapshot is a copy of the hub at the time of the operation. This feature is not normally used; it
is intended to help recover a system when replication has failed.
Initial load
NOTE: The HMX Manager appliance is configured as hub by default.
When an HMX Manager appliance is registered as spoke server into another HMX Manager
appliance, all the data in the spoke is deleted and overwritten with the data from the hub. This
process is called initial load. Once the initial load is completed, both HMX Manager
appliances have the same information.
Incremental updates
The incremental updates are done by the pull and push tasks which are executed every period
of time (by default 1 minute) by each spoke. The push task takes care of sending all the
changes to the hub, while the pull task retrieves changes from the hub.