High Availability – HA

HA High availability instaelearn.com
HA High availability instaelearn.com


For any business-critical operations, be it the concern of a single point of failure or load sharing, the concept of high availability has been around for quite some time. This is also referred to as HA, redundancy, etc. even though the idea remains the same.

The uptime of networking or network components is getting more and more crucial as the technology is growing out vertically as well as horizontally. For the workforce to stay productive almost all businesses are being dependent on the network and computing device to be running and available to perform designated tasks. Talking about real-world scenarios, the sweetest network can have trouble in paradise anytime. There could be ‘n’ number of reasons for any piece of hardware to malfunction or stop functioning. Now, this could be due to issues with the device logically or maybe something physical in nature. Some of the examples could be due to a power outage, NIC card failure, device failure, memory or CPU high utilization, routing engine failure PID crash, etc. Now one approach could be to keep a device ready and get immediately replaced by, as soon as the issue occurs, which we suppose would not be a preferred situation to be in. This would also require the availability of an engineer as well in times of crisis. Who would want to receive calls at 2 AM, to rush to office as some users are not able to work due to gateway device down? Another reason for having HA is to add the device in redundancy for load sharing which is otherwise also known as active-active deployment.

To completely understand the function of HA, you need to have a fundamental understanding of downtime and availability. Any network or system administrator would prefer to keep the downtime to 0% and availability to 100%. Once you get a hang of these terms it would be pretty easy understanding the need for HA. We have a cook step by step process on how to calculate them.

We hope that you already understand the concept of availability and downtime, let’s get down to our topic for today and why is it so important in these challenging times.

Why do we need HA?

Even a short period of downtime can cause consequential losses for your business and damage to its brand reputation. Direct financial losses can prove significant to a business, but the loss of trust among customers can create long-term barriers to the success and growth of the business. For customers its simple, they need someone on whom they can rely on and ensure that the product and services they pay for is worth enough.

The purpose of HA architecture is to ensure that your server, network, or application can endure different demand loads and different types of failures with the least possible downtime. By using best practices designed to ensure high availability, you help your organization achieve maximum productivity and reliability. The primary goal of HA is eliminating single failure points in your systems and infrastructure that would lead to interruption of your operations or services. Redundancy — along with methods for spotting failures and taking corrective actions — helps keep your systems up and running at peak efficiency.

Types of HA Concepts

Now that we have understood what high availability is, let’s see how we can achieve it. When we talk about computing it’s a wide range and type of devices and software. Every single component is dependent and survives in a single ecosystem. We will briefly discuss, some of the types of HA concepts that we have in our arsenal.

  • Network Load Balancing
  • Fail Over Solutions
  • Geographical redundancy
  • Clustering

Network Load Balancing

Load balancing is an effective way of increasing the availability of critical services. When device failure is detected, they are seamlessly replaced, and the traffic is automatically redistributed to devices that are still running. Not only does load balancing lead to high availability it also facilitates incremental scalability i.e., for example, using the power of 2 CPU’s on 2 differently nodes working together as a unit. It also facilitates higher levels of fault tolerance within the service applications. From an end-user perspective, there will be a minimum to no glitch or issue observed if something broke, until the HA peer is functioning. This is being used more and more in the current world. We can see this widely being used in mission-critical server/application/networks.


Fail Over Solutions

Failover can be termed as the ability to seamlessly and automatically switch to a reliable backup system. A redundant or standby server or network should be ready to replace any previously active device upon its abnormal termination or failure. Failover can also be used in scenarios where you would like to apply a critical patch and keep a backup ready in case of an unknown issue due to Bugs and Vulnerability. Failover is also essential to disaster recovery, all standby core computing devices must themselves be immune to failure.

HA High availability instaelearn.com


Geographical redundancy

Nowadays we can see more and more global companies or SMB’s having multiple locations following a trend of having their network infrastructure spread out. No business is immune to natural disasters or accidents like earthquakes, floods, fire, etc. Business is expected to be running as usual and provides services is being the new normal. We can use an approach to spread out the location geologically in different cities, countries, or even continents. Be it health services or banks t is crucial to run independent stacks in each of the locations so that in case there is a failure in one location, the other can continue running. 



Even with the highest quality of engineering or equipment, all application services are bound to fail at some point. High availability is all about delivering application services regardless of failures. Clustering can provide instant failover services in the event of a fault. Any device that is ‘cluster-aware’ is capable of calling resources from multiple nodes; it falls back to a secondary node if the main node goes offline. A High Availability cluster includes multiple nodes that share the same configurations. This means that any node can be disconnected or shutdown from the network and the rest of the cluster will continue to operate normally if at least a single node is fully functional. Each node can be upgraded individually and re-joined while the cluster operates.

The image above Fig 1 shows a classic network cluster – known as stacking. The switches are connected via stacking cable in a daisy chain fashion. Post stacking all the 4 switches will be managed by a single IP. They will also behave like a single unit. If a node in the stack fails only the ports connecting to nodes fail. All other switches in the stack will continue to work as normal.

Likewise in Fig 2 shows a classic example of a server cluster. A production and an DR setup. All data in replicated amongst both the clustered nodes and in event of failure the redundant node in the cluster pick up the ongoing task.


How to Configure HA?

Now that we have a fundamental understanding of High-Availability, we will discuss how different OEM’s provide them and how can we deploy them in our environment. There are different terms that different OEM’s use but all of them boil down to making the systems available and ensure maximum uptime. We will be discussing high availability for the following:



Palo Alto


Click on the products that you want to check how to configure HA on for detailed steps.

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