What is a good SLO target?

It depends on what users notice and what the business needs, not on how many nines you can fit on a slide. Most user-facing SaaS lands between 99.9% and 99.95%; internal or batch systems often sit lower on purpose to leave room to ship. Pick the lowest target your users are happy with, because every extra nine costs disproportionately more to hold.

What is the difference between an SLO and an SLA?

An SLO is an internal target you manage to. An SLA is an external contract with penalties if you miss it. The SLA is almost always set looser than the SLO, so the internal target trips first and gives you room to react before a customer is owed credits.

Service Level Objective (SLO)

A Service Level Objective is the target reliability you commit a service to, written as a number like 99.9% of requests succeeding over a 30-day window.

also: SLO · service level objective · availability target

99.9% over 30 days≈ 43m downtime / monththe budget a single 'three nines' target permits

An SLO is a line you draw in advance: the fraction of requests (or minutes) that must succeed for the service to count as healthy. It is measured against a Service Level Indicator (SLI), the actual metric you track, such as the share of HTTP requests that return without a 5xx, or the share served under 300ms.

The number matters more than it looks. The gap between 99.9% and 99.99% is the difference between about 43 minutes and about 4 minutes of allowed downtime a month. Each extra nine costs roughly ten times the engineering work of the one before it, so picking a target your users actually need (rather than the most nines you can write down) is a budgeting decision, not an aspiration.

A good SLO is the contract the rest of your reliability work hangs off. It tells you when to keep shipping features and when to stop and fix the system, and it gives on-call a clear definition of whether something is an incident that does not depend on who is awake.

free_toolSLO & Error Budget CalculatorTurn an availability target into the downtime, failed requests, and burn rate it allows.

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Questions & answers

What is a good SLO target?: It depends on what users notice and what the business needs, not on how many nines you can fit on a slide. Most user-facing SaaS lands between 99.9% and 99.95%; internal or batch systems often sit lower on purpose to leave room to ship. Pick the lowest target your users are happy with, because every extra nine costs disproportionately more to hold.
What is the difference between an SLO and an SLA?: An SLO is an internal target you manage to. An SLA is an external contract with penalties if you miss it. The SLA is almost always set looser than the SLO, so the internal target trips first and gives you room to react before a customer is owed credits.

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