A combination of architectural planning, infrastructure configuration, and operating procedures is needed to achieve high availability in Azure.
In order to provide high availability, Azure offers a range of products and services. To take proper advantage of these offers, your application architecture must be carefully designed and implemented.

Following the steps stated hereunder can be highly beneficial in achieving high availability

(a) Distribute your application across multiple Azure regions or availability zones. By doing this, you can be sure that even if a region or zone experiences outage, your application will still be accessible in other areas. Azure availability zones are physically and logically separated datacenters with their own independent power source, network, and cooling. Being connected with an extremely low-latency network, make availability zones to become a building block to delivering high availability applications

(b) Use Virtual Machine Scale Sets(VMSS) to deploy and manage a set of identical VMs. This provides high availability and resiliency.

(c) With the use of Azure Load Balancers you can distribute incoming traffic across multiple instances of your application. These ensure that if one instance becomes unavailable, traffic is automatically routed to healthy instances.

(d) Implementing auto scaling helps to dynamically adjust the number of instances based on demand. Such services include Azure Virtual Machine Scale Sets, Azure Kubernetes Service (AKS), and Azure App Service

(e) Replicating your database across multiple regions ensures data availability and disaster recovery. Azure SQL Database or Azure Cosmos DB offers built-in replication and failover capabilities

(f) Distributing user traffic across multiple endpoints in different regions by using Azure Traffic Manager.

(g) By setting up Azure Monitor you will be able to continuously monitor your application and infrastructure. Configure alerts to notify you in case of low performance, downtime, or any other issues that could impact availability.

(h) Plan for disaster recovery to handle unexpected failures or outages. Utilize Azure Site Recovery to replicate your virtual machines and data to a secondary region, ensuring business continuity in case of a major outage.

(i) Use serverless computing services like Azure Functions and Logic Apps for critical business processes. These services automatically scale and provide high availability without the need to manage underlying infrastructure.

(j)Utilize Azure Monitor and Azure Application Insights to monitor the health and performance of your applications and services. Set up alerts to notify you of any issues or potential downtime.

To ensure a proper use and effective combination the Azure tools highlighted above towards achieving high availability, consider the following guidelines in designing and building your Architecture

(1)Specify the availability criteria: Identify the cloud workloads that require high availability and their usage patterns. Define your availability metrics. These can include:

• Percentage of Uptime
• Average time for Recovery
• Average time lapse between failures
• Recovery Time Objective
• Recovery Point Objective Use a combination of these variables to decide your projected Service Level Agreement (SLA) for each application workload. Microsoft defines its own SLA for each Azure service which you can leverage on. Verify what the services' SLA guarantees so that you can set up redundant components with failover if you need a greater SLA than Azure guarantees.

(2)Create a High Availability Architecture plan: Start by ascertaining the potential failure types, their implications, and recovery options. Define the amount of redundancy needed for each component based on taking the preceding step. Use load balancing to distribute requests among redundant components to prevent single points of failure. Costs of implementation should be considered, resiliency, data replication and documentation of steps taken

(3)Carry out End-to-End Testing: The followings can be tested to know different failure scenarios that can be envisaged

• fault level
• failures under load
• health probes
• monitoring systems

(4)Deploy Applications on a regular basis by observing the following guidelines

• An automated, regular deployment process can reduce the likelihood of errors and failures, and make recovery easy
• Try to achieve rolling updates that do not require downtime of essential components
• Deployments should be automated to allow you to spin up a complete environment representing your best configuration.

(5)Monitor Application Health: These can be achieved by performing the actions stated below

• To quickly detect failure, use probes and check functions
• Monitor degrading health metrics
• Check subscription limits
• Regular logging and auditing

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