Network Monitor Dependency Guidelines
Dependencies allow you to create a hierarchy of checks that depend on each other. This hierarchy is independent of the Folder structure of your Network Monitor configuration. Dependencies prevent you and your network administrators from being overwhelmed with alert notifications when a central router or server goes down. Without a dependency configuration, the failure of a central server or device would cause a failure of other servers, and as a result many alert notifications would be sent out. There are at least two items involved when configuring dependencies:
- Dependee - the server or device that plays a central role. A failure of this 'dependee' device or server would cause failures of other servers and devices (so called 'dependers');
- Depender(s) - servers, devices or folders that depend on the 'dependee'.
The following example illustrates the use of dependencies:
Figure 1: Sample network.
Figure 1 shows a configuration with 3 folders in the root:
- LAN Servers - Local Area Network servers
- Routers - A Router folder that contains only one item: an Internet Gateway
- WAN Servers - Server on the public internet, including mail servers and web servers
When the Internet Gateway fails, all WAN servers will fail, and notifications will be sent out for all WAN servers. See also Figure 2 and Figure 3.
Figure 2: The Internet Gateway fails.
Figure 3: As a result, all WAN servers appear not available.
Configuring Dependencies for the Sample Configuration
From the Tools menu, choose Dependencies..., and make the 'WAN Servers' Folder dependent of the 'Internet Gateway' (figure 4)
Figure 4: 'WAN Servers' will depend on the Internet Gateway
Figure 5: As a result, the WAN servers become orange, indicating that a dependee failed.
All WAN servers are now marked by an orange icon, indicating that a dependee failed.
Only one notification will be sent out, indicating that the Internet Gateway failed.
When selecting the Root, you have an overview of your network, showing the failed Internet Gateway and the dependent WAN servers (figure 6)
Figure 6: Overview of the network when the Internet Gateway fails.
A dependee cannot be a Folder, only a Check (device or server). You can make Checks and/or Folders dependent of the dependee. It is recommended to use Folders rather than Checks as a depender, because it is dynamic: when you want to monitor a new WAN Server, you do not need to change the Dependency configuration. When you configure individual Checks as a depender, you have to.
Figure 7: NOT RECOMMENDED: using individual depender checks
It's a good practice to define a small monitor scan interval for the dependee checks, for instance once every 10 seconds. This way, you get a more accurate view of the network. If the Internet Gateway is only scanned once every 2 minutes, and your WAN servers also, it may take up to 4 minutes before the WAN server becomes 'orange' when the Internet Gateway fails. By defining a smaller scan interval for the Internet Gateway, it will be less.