We can look more deeply at the industry standard of five nines of availability against fewer nines. We can use the term Service Level Agreement (SLA) to understand the contract between the end user and the Kubernetes operator that guarantees the availability of the underlying hardware and Kubernetes software to your application owners.

A SLA is a guaranteed level of availability. It's important to note that the availability gets very expensive as it increases.

Here are a few SLA levels:

• With an SLA of 99.9% availability, you can have a downtime of:
  • Daily: 1 minute, 26.4 seconds
  • Weekly: 10 minutes, 4.8 seconds
  • Monthly: 43 minutes,  49.7 seconds
  • Yearly: 8 hours 45 minutes, 57.0 seconds
• With an SLA of 99.99% availability, you can have a downtime of:
  • Daily: 8.6 seconds
  • Weekly: 1 minutes, 0.5 seconds
  • Monthly: 4 minutes, 23.0 seconds
  • Yearly: 52 minutes, 35.7 seconds
• With an SLA of 99.999% availability, you can have downtime of:
  • Daily: 0.9 seconds
  • Weekly: 6.0 seconds
  • Monthly: 26.3 seconds
  • Yearly: 5 minutes, 15.6 seconds

As you can see, with five nines of availability, you don't have a lot of room to breathe with your Kubernetes cluster. It's also important to note that the availability of your cluster is a function of the application's availability.

What does that mean? Well, the application itself will also have problems and code errors that are outside of the domain and control of the Kubernetes cluster. So, the uptime and availability of a given application is going to be equal to (and rarely if ever equal, given human error) or less than your cluster's general availability.

So, let's figure out the pieces of HA in Kubernetes.