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Subject:	RE: Beginner understanding templates
Author:	Jane Curry
Posted:	2017-09-28 09:51

Hi Marco,
I wish I could point you to a good explanation on templates!  Let me have a go at it.....

A template has a name and a location:

• name        can be almost anything. Examples provided with the product are Device and FileSystem
• location    is the device class in which a monitoring template is contained (and nothing whatsoever to do with the Zenoss Location groupings that can be used in the GUI). This is determined when the template is created by associating it with the highest point in the
  Zenoss device class hierarchy tree where this template may be bound (I'll come back to "binding" in a moment).

There may be many different instances of a template with the same name - look at the Device template; there's one for /Server/Linux, /Server/SSH,  /Server/Windows and so on.  They all contain different data sources (definitions of things to collect (data points) and how to collect them), so the Linux one uses snmp, the SSH one uses ssh and the Windows one uses WMI.  Each of the different instances of the Device template also contains graph definitions, using the datapoints defined.  Ultimately in the GUI, the graphs may look very similar - CPU Utilization, Memory etc - but that data may have been collected by very different methods.

These templates are all just definitions - they don't actually DO anything until they are "bound".  Zenoss provides some template bindings as default out-of-the-box; you can add, change, remove as you wish.  Templates can be bound to a device class or to a specific device and the template instance "lowest" in the class hierarchy is what will actually run on a box, so a device-level binding for a device fred in /Server/Linux/myBoxes, would override any Device template defined for class /Server/Linux/myBoxes, which in turn would override any Device template defined for class /Server/Linux, which in turn would override any Device template for class /Server, etc.

A large part of Zenoss's scalability is to apply templates at the highest possible level so that if changes are needed, they then are automatically applied to lots of devices.  Only change an instance of a template if it really needs to do something different at that level of the hierarchy.  And to answer one of your specific questions, yes - a Device template at device class /Server/Linux would apply to any device in /Server/Linux, /Server/Linux/myBoxes and on down the hierarchy, unless overridden.

In addition, both a device and a device class have a "Configuration Property" (also known as a zProperty), called zDeviceTemplates.  This is a list of the template names bound at that level - just the name; it is up to Zenoss to determine which instance of that template name is appropriate to use.

A frequent confusion with templates is the difference between device-level templates (like Device) and component templates.  If you look at ADVANCED -> Monitoring Templates and look at all the templates, some have a small icon (white snowflake on grey background) - this means it is a component template.  Unfortunately this isn't / hasn't always been totally consistent but it is generally a good guide.  An example of a component template is FileSystem; again, there are several different instances for the different parts of the device class hierarchy.   A component template is automatically bound to any relevant component - where a component is something in a device's main page under the left-hand Components menu - things like File Systems, Interfaces, Processors.  These components are discovered by modeling ( zenmodeler typically runs every 12 hours).  You should not manually bind a component template.

So, bottom line, if you put a device under /Server/Linux and you ensure that the Configuration Properties for SNMP are setup correctly, then the Device (/Server/Linux) device-level template should run on it, collecting CPU, memory, IO data every 5 minutes.  zenmodeler should be able to discover at least Interface and File System components; once discovered, the FileSystem (/Server/Linux) component template will automatically be bound to each FileSystem instance.

Cheers,
Jane

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Jane Curry
Skills 1st United Kingdom
jane.curry@skills-1st.co.uk
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