How to achieve High Availability in Microsoft Azure
Published: 2023-05-20 14:53:17

Most enterprises run mission- critical applications and services hence require very reliable systems and platforms to host such applications and solutions with minimum tolerance to downtime. Hosting on-premise is an option; however, cloud models offer so many comparative benefits of which high reliability (availability) is a critical one. Azure as one of the three leading cloud providers offers various tools and features that enables it offer high availability of its services and resources to organizations. This article conceptualizes high availability in Azure.

**What is high availability**
High availability ensures maximum potential uptime by the elimination of all points of failure to enable continious operation of applications even if one of the IT components it depends on fails. This is very critical for systems that cannot tolerate interruption in service and any downtime can result in gross financial losses, for instance network traffic is dependent on stable links but for high availability additional links are required for redundancy. If the main link fails traffic failover to the redundant path. In cloud technology, IT disruptions are mimimized via redundancy,failover and fault tolerance mechanisms. 
For a systems to be highly available there must be an assurance of a certain percentage of uptime backed by a Service Level Agreement (SLA) ,for instance a system with 99.99% uptime will still be down 0.01% of the time ; hence no system is perfect.Note that reliability will still depend on the number of components, their configuration settings, and the resources allocated to each component. 

Creating a highly available system requires three main characteristics:
**Redundancy** which ensures that systems critical operational elements have additional redundant components that can take over in case of failure
**Monitoring** collection of revenant data from a running system to detect when a likely failure will occur so that proactive actions will be taken
**Failover** switching from active component to a redundant one whenever monitoring indicates failure of the active running component. 

**Steps required to achieve high availability**
**Deploying Azure resources in paired regions:** Azure region is a set of datacenters, deployed within a latency-defined perimeter and connected through a dedicated regional low-latency network   Each region is paired with another in the same geography example Canada Central paired with Canada East 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 make it's services available, hence deploying resources in the two regions that are paired provides high availability should one region fail. 

**Deploying Azure Resources across multiple Availability zone:** Azure offers yet another degree of availability protection via availability zones. Azure availability zones are physically and logically separated datacenters with their own  power source, network, and cooling.but connected with an extremely low-latency network,hence they become a building block to delivering high availability applications. There are a minimum of three availability zones per region, although not all regions are availability zone enabled. Deploying Azure resource in multiple availability zones ensures the resource will be available in the event of failure on one of the zones. 

**Availability Sets**

Availability sets as a feature of Azure assist to prevent potential outages caused by hardware and updates issues,
The 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, while an update domain is a logical group of hardwares that undergo maintenance activities or rebooting at the same time.
An availability set distributes virtual machines across multiple fault domains and update domains which assist to prevent outages caused by a power or networking failure in a fault domain and also enables the virtual machines to be updated or maintained within their respective update domains without causing the set as a whole to be unavailable.

**A virtual machine scale set**
Azure Virtual Machine Scale Sets enables you create and manage a group of load balanced virtual machines. A scale set can automatically scale out or scale in to adapt to changes in demand.
Load balancer regulates automatically to ensure that the access to the virtual machines in the set is balanced across virtual machines appropriately as virtual machines are added or removed from the set.hence
scale sets enable high availability for virtual machines,resources and the services that depend on them
.
 **Monitor and Automate:**
 For proactive identification and resolution of issues that may impact availability monitoring and automation are critical. Azure provides several monitoring and alerting services such as Azure Monitor, Azure Log Analytics, and Azure Application Insights that facilites collection and analyzing of telemetry data from applications and resources. By setting up automated alerts and notifications based on predefined thresholds or anomalies,detection and response to issues in real-time is made possible. Besides, Routine tasks, such as scaling, backups, and patching are automated using Azure Automation and Azure Logic Apps hence ensuring that your resources are always optimized for high availability. 
Utilizing these measures applications hosted in Azure will definitely be highly available.