High Availability in Cloud

There are normally coupled with SLAs – Service Level Agreements. Each cloud service provider and their services having different SLAs depends upon its high availability, redundancy, fault tolerance etc. A service-level agreement (SLA) is a commitment given by a service provider.

High Availability – System will continue to operate despite the complete failure of any of its internal or external component of the architecture. This is determined by the percentage of of uptime as show as 9s in below table

Fault Tolerance – System will continue to operate without any degradation of its performance despite of failure of any components.

Redundant – Have multiple resources dedicate to perform the same task

Availability %Downtime per yearDowntime per quarterDowntime per monthDowntime per weekDowntime per day
90% (“one nine”)36.53 days9.13 days73.05 hours16.80 hours2.40 hours
95% (“one and a half nines”)18.26 days4.56 days36.53 hours8.40 hours1.20 hours
97%10.96 days2.74 days21.92 hours5.04 hours43.20 minutes
98%7.31 days43.86 hours14.61 hours3.36 hours28.80 minutes
99% (“two nines”)3.65 days21.9 hours7.31 hours1.68 hours14.40 minutes
99.5% (“two and a half nines”)1.83 days10.98 hours3.65 hours50.40 minutes7.20 minutes
99.8%17.53 hours4.38 hours87.66 minutes20.16 minutes2.88 minutes
99.9% (“three nines”)8.77 hours2.19 hours43.83 minutes10.08 minutes1.44 minutes
99.95% (“three and a half nines”)4.38 hours65.7 minutes21.92 minutes5.04 minutes43.20 seconds
99.99% (“four nines”)52.60 minutes13.15 minutes4.38 minutes1.01 minutes8.64 seconds
99.995% (“four and a half nines”)26.30 minutes6.57 minutes2.19 minutes30.24 seconds4.32 seconds
99.999% (“five nines”)5.26 minutes1.31 minutes26.30 seconds6.05 seconds864.00 milliseconds
99.9999% (“six nines”)31.56 seconds7.89 seconds2.63 seconds604.80 milliseconds86.40 milliseconds
99.99999% (“seven nines”)3.16 seconds0.79 seconds262.98 milliseconds60.48 milliseconds8.64 milliseconds
99.999999% (“eight nines”)315.58 milliseconds78.89 milliseconds26.30 milliseconds6.05 milliseconds864.00 milliseconds
99.9999999% (“nine nines”)31.56 milliseconds7.89 milliseconds2.63 milliseconds604.80 microseconds86.40 microseconds
From Wikipedia

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