Leveraging a cloud computing model offers several benefits, both in financial cost and human resources. One of the reason companies choose cloud computing for their business operations is its High Availability which is the one of the Cloud computing benefits. Let us have some definitions of High Availability.

What is High Availability

High availability: Refers to a set of technologies that minimize IT disruptions by providing business continuity of IT services through redundant, fault-tolerant, or failover-protected components inside the same data center.

High availability: is a quality of computing infrastructure that allows it to continue functioning, even when some of its components fail. This is important for mission-critical systems that cannot tolerate interruption in service, and any downtime can cause damage or result in financial loss.

High availability: describes a system that is available for use without significant outages and that is generally backed by a service level agreement (SLA). For example, if a service has an SLA of 99.9 percent, the service is guaranteed to be available 99.9 percent of the time. Translated to the real world, that means the service can be unavailable no more than 43.2 minutes in a 30-day period to meet the 99.9 percent SLA for that month. A financially backed SLA provides a credit for the time in which the service was unavailable.

The basic elements of high availability
The following three elements are essential to a highly available system:
• Redundancy: ensuring that any elements critical to system operations have an additional, redundant component that can take over in case of failure.
• Monitoring: collecting data from a running system and detecting when a component fails or stops responding.
• Failover: a mechanism that can switch automatically from the currently active component to a redundant component, if monitoring shows a failure of the active component.

Before we talk about the ways on how High Availability can be achieved in Azure, let’s highlight another point which is the A 5-Step Azure High Availability Checklist

1. Define Availability Requirements. Identify the cloud workloads that require high availability and their usage patterns.
2. Plan your High Availability Architecture.
3. Perform End-to-End Testing.
4. Deploy Applications Consistently.
5. Monitor Application Health.

After we have known what High Availability is, the basic element and the checklist, Lets quickly go to how we can achieve High Availability in Azure. Bellow are the ways High Availability can be achieved in Azure

1. Deploying Azure resources in more than one region: Azure region is a grouping of data centers that interact to provide redundancy and availability for the services hosted within that region. For example, West US, Central US, and North Central US are three of many regions in the United States. Each region is paired with another in the same geography to allow for replication of resources across multiple data centers to reduce the effects of natural disasters, outages, or other potential events that would affect a given data center’s ability to serve up the services hosted in that data center.
   For example, when you are deploying a Virtual Machine in Azure and want to prevent the Virtual Machine from being fail when there is outage or factors that can cause failure, region pairing is one the ways to prevent this issue to occur.

2. Deploying Azure Resources such as Virtual Machine across multiple Availability zone: Azure offers another level of availability protection through availability zones. An availability zone is a physically separate zone within a region, each with its own power, network, and cooling. You might think of an availability zone as a data center, although the separation of power, network, and cooling defines the zone, not the physical data center. An availability zone might encompass more than one data center. There are a minimum of three availability zones per region, although not all regions offer availability zones.
   For example, assume you need to deploy a set of virtual machines (VMs) to host a line of business service but need to ensure that the service remains available in the event of a failure at one of the data centers hosting the VMs. You deploy VMs to an additional availability zone so that if an incident does occur at one of the data centers, the VMs in the other availability zone will unaffected.
   You must use availability zones if you want to achieve certain SLAs. For example, deploying VMs to two or more availability zones results in an SLA of 99.99 percent

3. Availability Sets: Availability sets are another feature of Azure that help to avoid potential outages caused by hardware issues, updates, or other events.
   The are two elements that enable availability sets are update domains and fault domains.
   A fault domain is a logical grouping of hardware that shares a power source and network switch, similar to a physical rack in a data center while an update domain is a logical group of hardware that undergoes maintenance activities or reboot events at the same time.
   An availability set distributes VMs across multiple fault domains and update domains which helps guard against outages caused by a power or networking event in a fault domain and also enables the VMs to be updated or otherwise maintained within their respective update domains without causing the set as a whole to be unavailable.

4. Virtual Machine Scale Sets: A virtual machine scale set simplifies creating and managing a group of load-balanced VMs. A scale set can automatically scale out or scale in to adjust to changes in demand.
   Load balancing adjusts automatically to ensure that the access to the VMs in the set is balanced across VMs appropriately as VMs are added or removed from the set.
   Scale sets therefore enable high availability for your VMs and the services that rely on them.

Choosing Azure Cloud platform for your business guaranteed you a smooth continuous business operation and save you from system downtime.