Finding unique element types in XML with PowerShell

I recently needed to deal with a large (165MB) XML file, so the first question I had is: How many unique element types are actually in the file? I found a bunch of truly painful-sounding answers online, mainly involving the distinct-values() XPATH 2.0 function. If you've ever dealt with XPATH, you know that just setting up the toolchain environment to use it is pretty labor intensive. However, I then started looking for PowerShell cmdlets that work with XML and I found Select-Xml:

https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/select-xml?view=powershell-7

It looks nice enough, but it turns out that it has a few features that are really nice. Specifically, once you read in an XML document, your variable will have a Node member, and that member contains one member for each type of element in your document! So it automatically shows you the list of distinct elements. You can then maneuver through the members to find the number of each type of element ($myvar.Node.myelementType.count) or to view one of the instances ($myvar.Node.myelementType[0]), etc.

In my case, I found that my 165MB file (produced by the ITNM DLA) only contained about 17 unique element types, and that there were only about 2500 network devices, which I could then easily loop through to get the information I needed. Chained with ConvertTo-Csv, I was able to massage the data exactly as needed.

The moral of the story is: PowerShell is amazing right out of the box. I didn't have to add any new packages or anything, and it gave me precisely what I needed.

JRExecAction() function behavior in Netcool Impact

Just a short post today to set the record straight on the use of the JRExecAction() function in Netcool Impact policies.

The product documentation states that the JRExecAction() function returns nothing, but sets the variables ExecError and ExecOutput corresponding to stderr and stdout from the script/command that you run. However, the function itself returns the data written to stdout in addition to setting ExecOutput and/or ExecError. So if you try the following, you'll see that the same output is logged twice:


results = JRExecAction("/bin/ls", "/", false, 1000);
log(0,"Frank results = " + results);
log(0,"ExecOutput results = " + ExecOutput); 


Incidentally, the first use above is really the more common use in practice. You will find very few implementations where the ExecOutput variable is referenced.

How to reconfigure your ServiceNow MID server when your developer instance changes URLs

If your developer ServiceNow instance is hibernated, it may be assigned a new URL. This will break your MID server(s).

To fix this:

cd /servicenow/<midservername>/agent

vi config.xml

search for the old URL

update it

if the password has changed, put the new password in the file unencrypted. On startup, it will get encoded and encrypted.

./stop.sh

./start.sh

Go to your instance to check the status of your MID servers.

Customizing the ServiceNow Netcool Connector

UPDATE 5/1/2020

You can update this script through the ServiceNow GUI. The navigator item to select is "Script Files" under "MID Server". And the name of the script is NetcoolConnector. Edit in the GUI and it gets updated on all of your MID servers.

Background

The ServiceNow Netcool Connector (introduced at some point before the New York release) allows you to pull events from a Netcool ObjectServer into ServiceNow. The connector is a process that runs on a MID Server. Within the ServiceNow interface, there are only a few configuration options (userid/password, JDBC URL, how often to run, etc.). However, there are no filters to configure. That's because the connector is a straightforward Groovy script that you can edit as needed on the MID Server.

Details

The Netcool Connector script is found on the MID Server in the file .../agent/scripts/Groovy/NetcoolConnector.groovy. Some of the interesting parts of the script are the actual query that's run:

query = "select top 3000 Identifier,Node,NodeAlias,AlertKey, Manager,Agent,AlertGroup,Severity,Type,Summary,Acknowledged,LastOccurrence,StateChange,SuppressEscl from alerts.status where StateChange > " + lastTimeSignature + " and Manager not like '^.*Watch\$' order by StateChange asc";

That is exactly the query that's run, and you can edit it to include custom fields, for example. To complete the customization, you also need to update the createEvent() function to actually include those custom fields in the event that's created in ServiceNow. In there you can also do any hard-coded transforms that are required or anything else.