"Too often, a single, high-level SLO acts like a watermelon: green on the outside, but hiding red-hot problems within. That global compliance score can easily mask critical issues, creating a dangerous illusion of reliability. Averages hide outliers, and a 99.95% uptime might feel great until you realize it's hiding a 98% uptime for your most valuable enterprise customers or for an entire geographic region."
"To move beyond this illusion, we need to ask more sophisticated questions. It's not just "Are we meeting our SLO?" but "Are we reliable for all our users, in all circumstances?" This requires a two-pronged strategy: first, we must isolate the signal from the noise, and second, we must deconstruct our monolithic view of reliability into meaningful segments."
"One of the biggest sources of noise in SLO calculations is planned maintenance. Every SRE knows the feeling: you have a necessary database upgrade or a scheduled deployment, and you just have to accept that your error budget will take a hit. This is fundamentally flawed. An error budget should represent the acceptable level of unplanned failure. It's the currency you spend on innovation and risk."
"Wasting it on expected, planned downtime leads to three problems: It creates alert fatigue: Alarms go off for expected downtime, teaching teams to ignore them. It distorts your view of reliability: You can't easily distinguish between reliability impact from a real incident versus a planned change. It penalizes teams unfairly: A team's error budget is consumed even when they've done everything right."
A single overall uptime SLO can appear healthy while hiding severe problems affecting specific users, customer tiers, or regions. Averages can conceal outliers, such as lower uptime for enterprise customers or a particular geography. Reliability measurement should move beyond “meeting the SLO” to “being reliable for all users in all circumstances.” This requires isolating signal from noise and breaking a monolithic reliability view into meaningful segments. Planned maintenance is a major source of noise because it consumes error budget despite being expected. Error budget should reflect acceptable unplanned failure, not scheduled downtime. Treating planned downtime as a separate category reduces alert fatigue, improves incident versus change attribution, and avoids unfairly penalizing teams.
Read at New Relic
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