Standard : Service Availability (Uptime)

Description

Service Availability (Uptime) measures the percentage of time a system or service is operational and accessible to users as expected. It is a core indicator of system reliability and customer experience, commonly tracked using service-level indicators (SLIs) and expressed as a percentage (e.g. “four nines” = 99.99%).

Availability is often defined in your SLOs and directly tied to user trust, regulatory compliance, and business continuity.

How to Use

What to Measure

  • The ratio of time a service is available vs. the total time it is expected to be available.
  • Can be scoped by system, region, product area, or business-critical functionality.

Formula

Availability (%) = [(Total Time - Downtime) / Total Time] x 100

Instrumentation Tips

  • Use uptime monitoring tools (e.g. Pingdom, Datadog, Prometheus) and SLIs to track availability in real time.
  • Define meaningful failure states (e.g. slow response, partial outage) to reflect user-perceived availability.
  • Align measurements with your error budget and SLA expectations.

Why It Matters

  • Customer trust: Downtime directly impacts user experience and brand reputation.
  • Business continuity: High availability is essential for revenue-critical services.
  • Operational focus: Guides investment in resilience, failover, and redundancy.
  • Engineering alignment: Links technical health to user and business outcomes.

Best Practices

  • Define and publish SLOs that reflect real user needs.
  • Use synthetic checks and real-user monitoring to measure perceived uptime.
  • Set clear alerting thresholds and track alert precision.
  • Conduct incident reviews for any downtime outside of acceptable error budgets.
  • Continuously validate availability monitoring with failover testing.

Common Pitfalls

  • Only measuring endpoint ping checks—ignore user experience or partial outages.
  • Inflating availability stats by excluding maintenance or hidden downtime.
  • Tracking uptime manually or inconsistently across systems.
  • Lacking ownership or visibility into third-party service availability.

Signals of Success

  • Availability meets or exceeds SLOs over time.
  • Downtime causes are well-understood and resolved quickly.
  • Availability trends are part of engineering dashboards and OKRs.
  • Users experience stable, consistent access to your services.
  • [[Error Budget Consumption]]
  • [[Incident Frequency]]
  • [[Mean Time to Detect (MTTD)]]
  • [[Mean Time to Recovery (MTTR)]]
  • [[Service Level Objective (SLO) Compliance]]