SLI, SLO and SLA

An SLI is a measurement, such as the share of requests under 300 ms; an SLO is the target for it, such as 99.9 % per month; an SLA is the contractual promise, with penalties. The gap between 100 % and the SLO is the error budget.

Where it shows up in real systems

  • Metrics

    The four golden signals tell you something is wrong before users do. Without metrics, failures are only noticed when customers complain, which multiplies recovery time.

    In production: Prometheus, Datadog, Amazon CloudWatch, Grafana Mimir

  • Alerting and on-call

    Alerts need metrics to watch. Together they cut the time to detect and repair a failure from close to an hour to a few minutes.

    In production: PagerDuty, Opsgenie, Grafana OnCall, Prometheus Alertmanager

See it break, then fix it

Build an architecture, send it a day of traffic and outages, and learn why it holds or fails. Free to start.

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