Four nines or 99.99% availability

Luca Spiller
Head of Engineering
January 10, 2024

What is four nines?

Availability or uptime is often measured as a percentage which refers to the amount of time that a service is operational in a given period. Four nines availability refers to an uptime of 99.99%, which means downtime of less than 52 minutes and 9 seconds per year. 100% uptime would mean the service is availabile 24/7 without interuption.

What is an SLA?

Service providers typically have service-level agreements (SLAs) which define the level of service they will provide, and often they have a clause referrring to the availability, the number of nines, they must reach. If their downtime exceeds this amount, the SLA will often require the provider to pay some kind of compensation to the customer - often as a credit towards future service.

100% Availability Goal

The objective of a high-availability system is to attain 100% availability, but practical challenges may hinder achieving this goal. When a provider presents a Service Level Agreement (SLA), it signifies their assurance in the platform and the anticipated uptime it can deliver. Ensuring high availability is crucial, given that even a brief period of downtime can result in significant financial losses. Consider the ramifications of a stock market experiencing a mere 5-minute interruption.

How to prevent downtime?

To mitigate downtime, it's crucial to implement monitoring systems. WatchSumo is a great tool at monitoring your website's performance. It proactively identifies issues, such as a spike in response time, signaling potential problems that may lead to downtime. WatchSumo vigilantly observes your website for such indicators and promptly notifies you before any downtime occurs.

Calculating Downtime

99.99% in a day = 8.6s seconds of downtime

99.99% in a week = 1 minute of downtime of downtime

99.99% in a month = 4 minutes and 21 seconds of downtime

99.99% in a quarter = 13 minutes and 2 seconds of downtime

99.99% in a year = 52 minutes and 9 seconds of downtime

Other percentiles

Four nines of uptime is just one amount, other common 'nines' are as follows: