Working with NetDevices

NetDevices is the core of Trigger’s device interaction. Anything that communicates with devices relies on the metadata stored within NetDevice objects.


NetDevices reads in your netdevices.xml file that should be a dump of relevant metadata fields from your CMDB. If you don’t have a CMDB, then you’re going to have to populate this file manually. But you’re a Python programmer, right? So you can come up with something spiffy!

Here is what the netdevices.xml file bundled with the Trigger source code looks like:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Dummy version of netdevices.xml, with just one real entry modelded from the real file -->
    <device nodeName="">
        <budgetName>Data Center</budgetName>
        <lastUpdate>2010-07-19 19:56:32.0</lastUpdate>
        <make>M40 INTERNET BACKBONE ROUTER</make>
        <onCallName>Data Center</onCallName>
        <owningTeam>Data Center</owningTeam>
        <owner>12345678 - Network Engineering</owner>
        <projectName>Test Lab</projectName>

We plan to add support for different input sources including JSON, Sqlite, or “other” in the near future, but for now this is it.

By default the location of netdevices.xml can be specified one of two ways:

  1. Specifing the path in the NETDEVICESXML_FILE environment variable, or;
  2. modifying the value of of settings.NETDEVICESXML_FILE.

Getting Started

First things first, you must instantiate NetDevices. It has three things it requires before you can properly do this:

  1. The netdevices.xml file must be readable and must properly parse (see above);
  2. An instance of Redis.
  3. The path to must be valid, and must properly parse.

How it works

The NetDevices object itself is an immutable, dictionary-like Singleton object. If you don’t know what a Singleton is, it means that the actual there can only really only be one instance in any program. The actual instance object itself an instance of the inner _actual class which is stored in the module object as NetDevices._Singleton. This is done as a performance boost because many Trigger components require a NetDevices instance, and if we had to keep creating new ones, we’d be waiting forever each time one had to parse netdevices.xml all over again.

Upon startup, each <device> element found within netdevices.xml is used to create a NetDevice object. This object pulls in ACL associations from AclsDB.

The Singleton Pattern

The NetDevices module object has a _Singleton attribute that defaults to None. Upon creating an instance, this is populated with the NetDevices._actual instance:

>>> nd = NetDevices()
>>> nd._Singleton
<trigger.netdevices._actual object at 0x2ae3dcf48710>
>>> NetDevices._Singleton
<trigger.netdevices._actual object at 0x2ae3dcf48710>

This is how new instances are prevented. Whenever you create a new reference by instantiating NetDevices again, what you are really doing is creating a reference to NetDevices._Singleton:

>>> other_nd = NetDevices()
>>> other_nd._Singleton
<trigger.netdevices._actual object at 0x2ae3dcf48710>
>>> nd._Singleton is other_nd._Singleton

The only time this would be an issue is if you needed to change the actual contents of your object (such as when debugging netdevices.xml or passing production_only=False). If you need to do this, set the value to None:

>>> NetDevices._Singleton = None

Then the next call to NetDevices() will start from scratch. Keep in mind because of this pattern it is not easy to have more than one instance (there are ways but we’re not going to list them here!). All existing instances will inherit the value of NetDevices._Singleton:

>>> third_nd = NetDevices(production_only=False)
>>> third_nd._Singleton
<trigger.netdevices._actual object at 0x2ae3dcf506d0>
>>> nd._Singleton
<trigger.netdevices._actual object at 0x2ae3dcf506d0>
>>> third_nd._Singleton is nd._Singleton

Instantiating NetDevices

Throughout the Trigger code, the convention when instantiating and referencing a NetDevices instance, is to assign it to the variable nd. All examples will use this, so keep that in mind:

>>> from trigger.netdevices import NetDevices
>>> nd = NetDevices()
>>> len(nd)

By default, this only includes any devices for which adminStatus (aka administrative status) is PRODUCTION. This means that the device is used in your production environment. If you would like you get all devices regardless of adminStatus, you must pass production_only=False to the constructor:

>>> from trigger.netdevices import NetDevices
>>> nd = NetDevices(production_only=False)
>>> len(nd)

The included sample netdevices.xml contains one device that is marked as NON-PRODUCTION.

What’s in a NetDevice?

A NetDevice object has a number of attributes you can use creatively to correlate or identify them:

>>> dev = nd.find('test1-abc')
>>> dev

Printing it displays the hostname:

>>> print dev

You can dump the values:

>>> dev.dump()

        Owning Org.:       12345678 - Network Engineering
        Owning Team:       Data Center
        OnCall Team:       Data Center

        Manufacturer:      JUNIPER
        Make:              M40 INTERNET BACKBONE ROUTER
        Model:             M40-B-AC
        Type:              ROUTER
        Location:          LAB CR10 16ZZ

        Project:           Test Lab
        Serial:            987654321
        Asset Tag:         0000012345
        Budget Code:       1234578 (Data Center)

        Admin Status:      PRODUCTION
        Lifecycle Status:  INSTALLED
        Operation Status:  MONITORED
        Last Updated:      2010-07-19 19:56:32.0

You can reference them as attributes:

>>> dev.nodeName, dev.manufacturer, dev.deviceType

There are some special methods to perform identity tests:

>>> dev.is_router(), dev.is_switch(), dev.is_firewall()
(True, False, False)

You can view the ACLs assigned to the device:

>>> dev.explicit_acls
>>> dev.implicit_acls
set(['juniper-router.policer', 'juniper-router-protect'])
>>> dev.acls
set(['juniper-router.policer', 'juniper-router-protect', 'abc123'])

Or get the next time it’s ok to make changes to this device (more on this later):

>>> dev.bounce.next_ok('green')
datetime.datetime(2011, 7, 13, 9, 0, tzinfo=<UTC>)
>>> print dev.bounce.status()

Searching for devices

Like a dictionary

Since the object is like a dictionary, you may reference devices as keys by their hostnames:

>>> nd
{'': <NetDevice:>,
 '': <NetDevice:>,
 '': <NetDevice:>,
 '': <NetDevice:>}
>>> nd['']

You may also perform any other operations to iterate devices as you would with a dictionary (.keys(), .itervalues(), etc.).

Special methods

There are a number of ways you can search for devices. In all cases, you are returned a list.

The simplest usage is just to list all devices:

>>> nd.all()
[<NetDevice:>, <NetDevice:>,
 <NetDevice:>, <NetDevice:>]

Using all() is going to be very rare, as you’re more likely to work with a subset of your devices.

Find a device by its shortname (minus the domain):

>>> nd.find('test1-abc')

List devices by type (switches, routers, or firewalls):

>>> nd.list_routers()
[<NetDevice:>, <NetDevice:>]
>>> nd.list_switches()
>>> nd.list_firewalls()

Perform a case-sensitive search on any field (it defaults to nodeName):

[<NetDevice:>, <NetDevice:>]
>>>'NON-PRODUCTION', 'adminStatus')

Or you could just roll your own list comprehension to do the same thing:

>>> [d for d in nd.all() if d.adminStatus == 'NON-PRODUCTION']

Perform a case-INsenstive search on any number of fields as keyword arguments:

>>> nd.match(oncallname='data center', adminstatus='non')
>>> nd.match(manufacturer='netscreen')

Helper function

Another nifty tool within the module is device_match(), which returns a NetDevice object:

>>> from trigger.netdevices import device_match
>>> device_match('test')
2 possible matches found for 'test':
 [ 1]
 [ 2]
 [ 0] Exit

Enter a device number: 2

If there are multiple matches, it presents a prompt and lets you choose, otherwise it chooses for you:

>>> device_match('fw')
Matched ''.