I’ve been involved with the monitoring of computer networks for a long time, two decades actually, and I’m seeing an alarming trend. Every new monitoring application seems to be insisting on software agents. Basically, in order to get any value out of the application, you have to go out and install additional software on each server in your network.
Now there was a time when this was necessary. BMC Software made a lot of money with its PATROL series of agents, yet people hated them then as much as they hate agents now. Why? Well, first there was the cost, both in terms of licensing and in continuing to maintain them (upgrades, etc.). Next there was the fact that you had to add software to already overloaded systems. I can remember the first time the company I worked for back then deployed a PATROL agent on an Oracle database. When it was started up it took the database down as it slammed the system with requests. Which leads me to the final point, outside of security issues that arise with an increase in the number of applications running on a system, the moment the system experiences a problem the blame will fall on the agent.
Despite that, agents still seem to proliferate. In part I think it is political. Downloading and installing agents looks like useful work. “Hey, I’m busy monitoring the network with these here agents”. Also in part, it is laziness. I have never met a programmer who liked working on someone else’s code, so why not come up with a proprietary protocol and write agents to implement it?
But what bothers me the most is that it is so unnecessary. The information you need for monitoring, with the possible exception of Windows, is already there. Modern operating systems (again, with the exception of Windows) ship with an SNMP agent, usually based on Net-SNMP. This is a secure, powerful extensible agent that has been tried and tested for many years, and it is maintained directly on server itself. You can use SNMPv3 for secure communications, and the “extend” and “pass” directives to make it easy to customize.
But what about applications? Don’t you need an agent for that?
Not really. Modern applications tend to have an API, usually based on ReST, that can be queried by a management station for important information. Java applications support JMX, databases support ODBC, and when all that fails you can usually use good ol’ HTTP to query the application directly. And the best part is that the application itself can be written to guard against a monitoring query causing undue load on the system.
At OpenNMS we work with a lot of large customers, and they are loathe to install new software on all of their servers. Plus, many of our customers have devices that can’t support additional agents, such as routers and switches, and IoT devices such as thermostats and door locks. This is the main reason why the OpenNMS monitoring platform is, by design, agentless.
A critic might point out that OpenNMS does have an agent in the remote poller, as well as in the upcoming Minion feature set. True, but those act as “user agents”, giving OpenNMS a view into networks as if it was a user of those networks. The software is not installed on every server but instead it just needs the same access as a user would have. So, it can be installed on an existing system or on a small system purchased for that purpose, at a minimum just one for each network to be monitored.
While some new IT fields may require agents, most successful solutions try to avoid them. Even in newer fields such as IT automation, the best solutions are agentless. They are not necessary, and I strongly suggest that anyone who is asked to install an agent for monitoring question that requirement.