1 Przykłady użycia

Overview

This section presents examples of using preprocessing steps to accomplish some practical tasks.

Filtering VMware event log records

Using a regular expression preprocessing to filter unnecessary events of the VMWare event log.

1. On a working VMWare Hypervisor host check that the event log item vmware.eventlog[<url>,<mode>] is present and working properly. Note that the event log item could already be present on the hypervisor if the Template VM VMWare template has been linked during the host creation.

2. On the VMWare Hypervisor host create a dependent item of 'Log' type and set the event log item as its master.

In the "Preprocessing" tab of the dependent item select the "Matches regular expression" validation option and fill pattern, for example:

".* logged in .*" - filters all logging events in the event log
       "\bUser\s+\K\S+" -  filter only lines with usernames from the event log

Another approach that allows using matching groups and output control is to select "Regular expression" option in the "Preprocessing" tab and fill parameters, for example:

pattern: ".*logged in.*", output: "\0" - filters all logging events in the event log
       pattern "User (.*?)(?=\ )", output: "\1" - filter only usernames from the event log

Checking retrieved value type

This example uses the Custom multiplier preprocessing step to check if the retrieved item value type is numeric.

In the Preprocessing tab of an item, select the "Custom multiplier" preprocessing step and set the following parameter:

# Multiplies the retrieved value by 1:
       number: 1

Checking for not supported value

This example uses the Check for not supported value preprocessing step to check if the item value could not be retrieved.

When a Zabbix server/proxy poller process attempts to collect an item value, it may:

• Return a valid result.
• Return a result that initially seems valid but may become unsupported later (e.g., due to a value type mismatch after preprocessing).
• Return an error of collecting the value, causing the item to become unsupported. Common causes include:
  • Unknown item key (for Zabbix agent, Simple check, or Zabbix internal items)
  • Unknown OID (SNMP agent), unknown sensor (IPMI agent), or no JMX metric (JMX agent)
  • Cannot read trap file (SNMP trap)
  • Script not found (External check)
  • No such URL (HTTP agent)
  • Login failed (SSH agent, TELNET agent)
  • Invalid formula syntax (Calculated), JavaScript syntax error (Script), or invalid SQL (Database monitor)

To detect and handle errors of collecting item values, you can use the "Check for not supported value" preprocessing step. Note that this step is always executed first and only detects errors that occur before preprocessing begins.

In the Preprocessing tab of an item, select the "Check for not supported value" preprocessing step.

Then, use the Custom on fail option to discard the value (in this case, the error), set a custom value, or return a custom error message. Please note that discarded values are not stored in the database; as a result, triggers are not evaluated and trend data is not generated.