Trigger dependencies

We now have one service being watched. There are some more being monitored, so now we can try to create a trigger for an HTTP server. Let's assume that our host runs software that is a bit weird. The web service is a web email front-end, and it goes down whenever the SMTP server is unavailable. This means that the web service depends on the SMTP service.

Go to Configuration | Hosts, click on Triggers next to Another host, and then click on Create trigger. Fill in the following values:

• Name: Web service is down.
• Expression: Click on Add, and then again on Select next to the Item field. Make sure that Linux servers is selected in the Group drop-down and Another host in the Host drop-down, and then click on Web server status in the Name column. Both the function and its parameter are fine, so click on Insert:

This inserts the{Another Host:net.tcp.service[http,,80].last()}=0expression.

• Severity:  The value of this field should be Average.
• Description: Trigger expressions can get...