Uptime
ELI5 — The Vibe Check
Uptime is how long your service has been up and working without going down. It's usually expressed as a percentage like 99.9%. 'Three nines' (99.9%) sounds great but allows 8.7 hours of downtime per year. 'Five nines' (99.999%) is world-class and only allows 5 minutes down per year.
Real Talk
Uptime is the measure of time a system has been operational and available to users, typically expressed as a percentage. It's tracked against SLA commitments. The calculation is: (total time - downtime) / total time × 100%. High availability systems aim for 99.9% to 99.999% uptime.
When You'll Hear This
"What's our uptime for this month?" / "The SLA guarantees 99.9% uptime — we're below that this quarter."
Related Terms
Downtime
Downtime is when your app is broken and users can't access it. It costs money, damages reputation, and makes everyone's phone buzz with alerts.
Health Check
A Health Check is an automatic 'are you alive?' ping your infrastructure sends to your app regularly.
Monitoring
Monitoring is keeping a constant eye on your app while it runs — tracking whether it's up, how fast it responds, how many errors it throws, and how much me...
SLA (Service Level Agreement)
An SLA is a contract between you and your users about how reliable your service will be. 'We promise the app will be up 99.9% of the time.
SLI (Service Level Indicator)
An SLI is the actual measurement you track to know if you're hitting your SLO. If the SLO says 'be fast,' the SLI is the actual timer measuring speed.
SLO (Service Level Objective)
An SLO is the internal target you set for how well your service should run. It's like a personal fitness goal vs a race you signed up for.