Sysadmin 101: Alerting

This is the first in a series of articles on system administrator fundamentals. These days, DevOps has made even the job title "system administrator" seem a bit archaic, much like the "systems analyst" title it replaced. These DevOps positions are rather different from typical sysadmin jobs in the past in that they have a much larger emphasis on software development far beyond basic shell scripting. As a result, they often are filled with people with software development backgrounds without much prior sysadmin experience. In the past, sysadmins would enter the role at a junior level and be mentored by a senior sysadmin on the team, but in many cases currently, companies go quite a while with cloud outsourcing before their first DevOps hire. As a result, DevOps engineers might be thrust into the role at a junior level with no mentor around apart from search engines and Stack Overflow posts. In this series of articles, I'm going to expound on some of the lessons I've learned through the years that might be obvious to longtime sysadmins but may be news to someone just coming into this position.

In this first article, I cover on-call alerting. Like with any job title, the responsibilities given to sysadmins, DevOps and Site Reliability Engineers may differ, and in some cases, they may not involve any kind of 24x7 on-call duties, if you're lucky. For everyone else, though, there are many ways to organize on-call alerting, and there also are many ways to shoot yourself in the foot.

The main enemies of on-call alerting are false positives, with the main risks being ignoring alerts or burnout for members of your team. This article talks about some best practices you can apply to your alerting policies that hopefully will reduce burnout and make sure alerts aren't ignored.

Alert Thresholds

A common pitfall sysadmins run into when setting up monitoring systems is to alert on too many things. These days, it's simple to monitor just about any aspect of a server's health, so it's tempting to overload your monitoring system with all kinds of system checks. One of the main ongoing maintenance tasks for any monitoring system is setting appropriate alert thresholds to reduce false positives. This means the more checks you have in place, the higher the maintenance burden. As a result, I have a few different rules I apply to my monitoring checks when determining thresholds for notifications.

Critical alerts must be something I want to be woken up about at 3am.

A common cause of sysadmin burnout is being woken up with alerts for systems that don't matter. If you don't have a 24x7 international development team, you probably don't care if the build server has a problem at 3am, or even if you do, you probably are going to wait until the morning to fix it. By restricting critical alerts to just those systems that must be online 24x7, you help reduce false positives and make sure that real problems are addressed quickly.

Critical alerts must be actionable.

Some organizations send alerts when just about anything happens on a system. If I'm being woken up at 3am, I want to have a specific action plan associated with that alert so I can fix it. Again, too many false positives will burn out a sysadmin that's on call, and nothing is more frustrating than getting woken up with an alert that you can't do anything about. Every critical alert should have an obvious action plan the sysadmin can follow to fix it.

Warning alerts tell me about problems that will be critical if I don't fix them.

There are many problems on a system that I may want to know about and may want to investigate, but they aren't worth getting out of bed at 3am. Warning alerts don't trigger a pager, but they still send me a quieter notification. For instance, if load, used disk space or RAM grows to a certain point where the system is still healthy but if left unchecked may not be, I get a warning alert so I can investigate when I get a chance. On the other hand, if I got only a warning alert, but the system was no longer responding, that's an indication I may need to change my alert thresholds.

Repeat warning alerts periodically.

I think of warning alerts like this thing nagging at you to look at it and fix it during the work day. If you send warning alerts too frequently, they just spam your inbox and are ignored, so I've found that spacing them out to alert every hour or so is enough to remind me of the problem but not so frequent that I ignore it completely.

Everything else is monitored, but doesn't send an alert.

There are many things in my monitoring system that help provide overall context when I'm investigating a problem, but by themselves, they aren't actionable and aren't anything I want to get alerts about. In other cases, I want to collect metrics from my systems to build trending graphs later. I disable alerts altogether on those kinds of checks. They still show up in my monitoring system and provide a good audit trail when I'm investigating a problem, but they don't page me with useless notifications.

Kyle's rule.

One final note about alert thresholds: I've developed a practice in my years as a sysadmin that I've found is important enough as a way to reduce burnout that I take it with me to every team I'm on. My rule is this:

If sysadmins were kept up during the night because of false alarms, they can clear their projects for the next day and spend time tuning alert thresholds so it doesn't happen again.

There is nothing worse than being kept up all night because of false positive alerts and knowing that the next night will be the same and that there's nothing you can do about it. If that kind of thing continues, it inevitably will lead either to burnout or to sysadmins silencing their pagers. Setting aside time for sysadmins to fix false alarms helps, because they get a chance to improve their night's sleep the next night. As a team lead or manager, sometimes this has meant that I've taken on a sysadmin's tickets for them during the day so they can fix alerts.


Kyle Rankin is Chief Security Officer at Purism, a company focused on computers that respect your privacy, security, and freedom. He is the author of many books including Linux Hardening in Hostile Networks, DevOps Troubleshooting and The Official Ubuntu