What is high availability?

If you run enterprise workloads in a cloud environment, system components and services need to remain operational and accessible for extended periods without any interruption during planned or unplanned outages. This level of resiliency is known as high availabilityThe ability of a service or workload to withstand failures and continue providing processing capability according to some predefined service level. For services, availability is defined in the Service Level Agreement. Availability includes both planned and unplanned events, such as maintenance, failures, and disasters. . High availability is achieved by using redundant system components and services, and by distributing these components across different environments. IBM Cloud delivers highly available cloud services by using redundant components and eliminating single points of failure.

At the multizone regionsA region that is spread across physical locations in multiple zones to increase fault tolerance. (MZR) level, HA means having workloads running in multiple availability zonesA location within a region that IBM Cloud Kubernetes Service runs in. in the MZR, which provide the redundancy for local failures.

For HA in the cloud, it's important to understand the high-level concepts that you need to address if you're building or running a highly available cloud system.

Formula for high availability

A standard formula for high availability is MTBF/(MTBF+MTTR), where MTBF is "mean time between failures" and MTTR is "mean time to repair". Since MTBF is the time when the system is up, and MTTR is the time that the system is down, this formula can be summarized as follows:

Availability = (The time the system is up)/(The time the system is up + The time the system is down).

The formula is useful because it shows you how to improve availability. Consider a scenario where you require that the server is always available for a month of 30 days. In that month, let's say the server went down once for a total of 1 hr.

To get the total time in the month, multiply 30 days x 24 hrs/day = 720 hours MTBF = Total operating time / Number of failures = 720 hrs / 1 = 720 hrs MTTR = Total downtime / Number of failures = 1 hr / 1 = 1 hr Availability = (MTBF / (MTBF + MTTR)) x 100 = (720 / 721) x 100 = 99.86%

You can increase MTBF, decrease MTTR, or both. This means that availability can be improved by increasing reliability or fixing issues when they break more efficiently. Both approaches are common in computer systems. The mainframe, which uses high reliability parts, redundant parts, and modularity to allow quicker repairs, shows that significant levels of availability are possible with this approach. For more information about the availability of specific IBM Cloud services, see Service Level Agreements (SLAs).

Why do you need high availability?

With IBM Cloud, you can protect your critical workloads by deploying them onto a resilient, highly available infrastructure. By using the backup, disaster recovery, and high availability features, you can minimize downtime if a severe failure occurs. By creating cloud infrastructures that are protected against single points of failure, and backing up your data, you keep your workloads and applications highly available.

A resilient infrastructure keeps your cloud solution running, even if one or more infrastructure components experience a problem such as:

• Power loss in a data center
• Hardware failure in one of the data centers
• Network failure due to a virtual router issue
• Planned or unplanned maintenance of a service
• Limited blast radius natural disaster
• Ransomware attack on virtual server instance