High Availability Overview
Common Terminology
A table of common terminology used when describing our HA product is as follows:
Primary Server | The primary server is a fully configured and operational Management or Monitoring Server which actively collects live data. Primary Servers can be any Windows OS server in your environment that has been identified as critical component. Once a Primary Server has been identified a Secondary Server can be deployed. A Primary Server will be paired with a Secondary Server so that any changes made to the Primary Server will be automatically replicated by HA to the Secondary Server. |
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Secondary Server | The Secondary Server is one that is paired with a Primary Server. It only runs a minimal set of Prognosis executables and will be replicated with changes from the Primary Server. The Secondary Server hardware and software specifications should match those of the Primary Server. |
Active Mode | In Active mode, the Prognosis Server (Primary or Secondary) will be fully configured and operational which actively collects live data. Any configuration changes to the active server will be automatically replicated by HA to the passive server. Note that it is not possible to have a HA Pair in an active/active mode. |
Passive Mode | In Passive mode, the Prognosis Server runs only a minimal set of Prognosis executables and will be replicated with changes from the active server. The passive server will also stop any running Analysts, Thresholds or Databases that are currently running unless they are enabled specifically. Note that it is not possible to have a HA Pair in a passive/passive mode. |
Basic Topology
The current HA solution is designed to support the configuration of a HA Pair, whereby one server provides redundancy for the other server.
The setup and configuration for the HA Pair is performed via the Management Server and is most conveniently managed using the High Availability page in the Web Application - Administration tool.
In more complex topologies, where there are more than two levels of hierarchy within the topology, it is important when configuring HA, that it is always performed using the Global Management Server.
In this case, the Global Management Server should have the following characteristics:
- No other Managing Server manages the Global Management Server (or if there are, ensure that HA is not administered through that server)
- The Global Management Server manages all servers at the next level in the hierarchy that are to be configured in HA Pairs.
- NOTE: There is no restriction on numbers of Global Management Servers, so these can also be configured to be in a HA Pair.
A minimum set of servers required for implementing HA is a single Management Server and two Monitoring Servers. The Management Server should be configured to manage the two Monitoring Servers, as shown in the diagram below:
Synchronization refers to Prognosis Configurations only, no Database Collections are included in this synchronization.
Preparing the Environment for HA
Setup the Management Server
The Management Server simply needs to be configured to manage both the Primary and Secondary Servers either directly or with another intermediary Management Server.
For further details see how to Setup a Management Server.
Setup the Primary Server
When selecting a Monitoring Server to be used as the Primary Server:
- If the Monitoring Server was configured (using the Web Application - Administration tool) from a different Management Server than the Management Server selected above, issues may be seen when attempting to link the HA Pair, this is because configurations may not be correctly shared with the new Management Server for the Primary Server. This may cause the Secondary Server to be configured incorrectly, resulting in errors.
- Recommended: Perform a fresh install of Prognosis Server on the Primary Server, and re-configure using the HA Management Server.
Additionally, ensure that the network ports 5432 and 1970 are open. These are the default ports for PostgreSQL and the HA synchronization communications respectively. If different port numbers are desired, these can be configured.
Setup the Secondary Server
When selecting a (Secondary) Monitoring Server to link with an existing (Primary) Monitoring Server, it is recommended that a server with a fresh installation of Prognosis is used. This guarantees that no residual configurations will conflict with configurations that will be synchronized from the Primary Monitoring Server after pairing.
The same port requirements apply to the Secondary server as the Primary Server.
Configure the HA Pair
Once the minimal set of Servers above have been identified, use the Management Server to configure the HA Pair (Primary and Secondary Servers), for further instructions refer to Configuration for High Availability.