Availability

Overview Your company uses a cloud service with an SLA that clearly states 99.95% monthly availability. One night, the service goes down for 30 minutes. You file a compensation claim with the cloud provider. The calculation goes roughly: downtime as a fraction of total monthly minutes, multiplied by your monthly fee. Assuming you pay 1000 yuan/month, that’s 30 minutes divided by 43,200 minutes times 1000, giving you about 0.7 yuan....

Overview 99.5% availability sounds pretty good — until you do the math. A year has 8,760 hours. 99.5% means you’re allowed 43.8 hours of downtime. Per month, that’s roughly 3.65 hours of service interruption. If this is a core transaction system, those 3.65 hours could mean tens of thousands in lost orders. During a major promotion, the loss multiplies by orders of magnitude. 99.9%? Annual downtime drops to 8.77 hours, less than 44 minutes per month....

Overview Traditional monitoring is “passive” — it waits for users to access the system, triggering system behavior, then collects metrics and logs. This approach has a fundamental flaw: when monitoring detects a problem, users have already been impacted. If your homepage takes 10 seconds to load, your monitoring alert may not trigger for 5 minutes — by which time thousands of users have experienced poor performance. Synthetic Monitoring is a “proactive” monitoring approach — it simulates real user behavior, regularly accessing critical paths to discover and fix issues before users perceive them....