Apart from the main Nagios core engine, one can add several APIs and add-ons to make the Nagios engine more stronger without compromising it's performance.
Each config parameter can be easily tuned as per individual's need. Many proven frontends are available to get performance related output from the Nagios engine.
Also, Nagios can work without any database back end. It generates a single file for each day and maintains it in a separate directory until a Linux System Admin removes it manually. In Nagios terms, it is called archiving. When someone wants an availability report for a particular server for the last year, Nagios simply fetches all of the relevant files and outputs the data within the shortest period of time. There is no need to query any database to get historical data, which puts extra burden on CPU and memory.
Improvements to My Organization:
Using Nagios, I'm managing more than 1000 services, which involves the following operating nodes:
Red Hat Enterprise Linux
Windows enterprise-grade OS
FortiGate and WatchGuard firewalls
APC UPS systems
The majority of the above nodes support SNMP v1/2, thru which one needs to tune up the monitoring plug-in as needed.
Room for Improvement:
Considering my utilization of Nagios on a daily basis, it would be really great if Nagios can concentrate on the following areas of improvement:
Custom availability report and export as PDF
Nagios SLA. I'm currently working on Nagios Digger, which has many code-level problems. In my present configuration, I've observed PHP level coding issues. I'm able to fetch all Nagios data into the Nagios Digger database (mariadb in rhel7) successfully, but found difficulties fetching and replicating it into the PHP front end. I've already contacted its author and coordination is in progress to make it available for the community.
SMS tool integration with Nagios
Use of Solution:
I have been using Nagios for more than five years.
In Nagios Core, I haven't had any minor problems in terms of stability. If any did arise, I never knew about it....!!!
I require less customer service because I am using an open source product. But, sincere thanks to the Nagios community for providing excellent and prompt support as and when required.
Initial setup was very straightforward. Just check the official Nagios website (www.nagios.org) for installation instructions.
If a person has basic or in-depth level knowledge of all required network/server equipment, than he/she can easily implement Nagios.
Also, it is advisable to have proper knowledge of SNMP v1/2/3 with Nagios agents for Windows and Unix-like OS.
Other Solutions Considered:
I started learning and configuring out data centre monitoring system by using Zabbix and openNMS. But, finally I selected Nagios due to its very large user community and maximum tunable parameters.
Disclosure: I am a real user, and this review is based on my own experience and opinions.