1.What is high availability?
High availability (HA) – as the name suggests – is a term that describes the system’s components ability to continue functioning in a specified time frame. It can be measured relative to fully operational or 100% – in the industry, for example, a popular standard of availability for a product is “five 9s” (99.999%) availability.
To achieve the status of HA, all experts are unanimous that a product must be well-designed and its segments – well tested before it’s deployed in the field. A significant part of HA systems is, one way or another, developed with the notion of backup and failover processing and data storage and access. This means that all the individual components, which build up such a system must always be present. As a result, all elements are duplicated to evade single points of failure.
If one of the elements fails, the failover process is activated, and it transfers the processing to the backup component. This method returns everything to normal in just a matter of microseconds. And the higher the percentage of availability to a system, the more open the failover is to the user.
2.What is high availability infrastructure?
Increasing the components of a system does not automatically turn it into a high-availability system. On the contrary, the greater the system’s complexity, the greater its risk of failure.
Data sharing, applications, and e-commerce websites are just some of the places where you will find almost unanimous utilization of HA clusters.
As mentioned earlier, HA solutions create redundancy within a cluster to eliminate any single point of failure.
This includes multiple network connections and data storage, and they can be redundantly linked through geographically diverse storage area networks.
Modern architectures also use load balancing – it distributes workloads across multiple instances such as a network or a cluster.This helps optimize resource usage, maximize performance, minimize response times, and avoid overburdening any device.
3.Main Benefits of HA
Availability & Five 9’s Uptime
The industry benchmark for measuring uptime is the five nines.
This metric can be applied to
- the entire system
- the system processes
- the software running within an infrastructure.
The more “9’s” an HA system has, the higher its uptime. The aim of a HA system is to provide as little downtime as possible and the framework to continue to provide the desired services.
Uptime is one of the most significant properties of a high-availability device. Uptime is essential, mainly when a system’s function is to offer a critical service – for example, air traffic control. In such scenarios, even a millisecond of delay could be the difference between life and death.
A high availability system is needed in business to ensure that a critical service is available at all times.
If the system encounters a problem – for example, a traffic spike or a rise in resource demand, it should be able to scale to meet those needs on the go. By integrating features like these into the system, the system would adapt rapidly to any changes in the architecture’s processes’ structural functionality.
If an error appears, the system can adjust and compensate while staying up and operating.
This form of structure necessitates forethought and contingency planning. One of the essential characteristics of a high availability system is anticipating problems and preparing for them in advance.
4.What is “Split Brain” and how to solve it
When nodes in a cluster of servers deviate from each other and face conflicts in dealing with incoming I/O operations, we have a split brain situation. This could result in the servers inconsistently recording similar data, or they may contend for resources. Such a scenario could turn off the cluster while the nodes anticipate proper guidance to resolve the conflict. You may experience downtime on your servers or even data corruption as a result of such an error.
To solve and prevent a split brain situation there are some techniques in hand.
Fencing and Quorum.
Fencing: The fencing mechanism removes failed nodes, resources, etc., and it doesn’t have a fixed max amount of nodes – which means that it can be used in both small & large clusters. Some fencing mechanisms like STONITH are there for you to shoot the other node in the head (basically power off or reboot) if required.
Quorum: In order to avoid split brain or diverging data of replicas system admins has to configure fencing. It turns out that in real world deployments node fencing is not popular because often mistakes happen in planning or deploying it. Also, Fencing is easy to set up in 2 nodes, but it’s becoming harder to configure when you have to set up 3 or more nodes. This is where Quorum comes into the picture, with the quorum set up and a cluster gets started, all nodes communicate with each other and aim to achieve quorum. As soon as a majority of the cluster is formed, there is a quorate cluster and resources can start.
5.Possible HA Implementations
One of the methods for achieving HA is by using multiple application servers. If you experience a sudden surge in traffic, your server may shut down, and requests from it can’t be made – which inevitably leads to more downtime.
To avoid such scenarios, applications are deployed by using redundant components – across several servers – and if one fails, the rest can take the extra load. This allows for a high fault tolerance.
Another method for achieving HA is by scaling databases, application stacks etc. HA is perhaps the most widely-used method to save and protect the data of your users. As an organization leader knows, losing such vital information can often be a very costly experience. Application stacks are also a subject to HA, therefore many modern applications needs to be Highly Available for the best user experience.
Finally, HA can be achieved by also spreading the servers across multiple geographical locations. Political events, natural disasters, failures of the electric grid can all lead to a shut down of your servers – even if they are several but clustered in one geographic location. To ensure the safety of the data and complete protection, modern solutions spread their servers worldwide. This further increases their reliability and allows for flexible disaster recovery plans.
Why choose LINBIT High Availability?
The creators of DRBD – LINBIT have over 20 years of experience in storage, high availability systems, and disaster recovery. This is why LINBIT is proud to provide HA services to other notable companies and organizations.
Many of them choose LINBIT HA because of the lack of vendor lock-ins – the clients pay only in respect to what they use and are accessible at any moment to switch to other platforms.
LINBIT HA can handle almost anything – from databases to file servers, storage targets, and application stacks.
And all those services – while maintaining low TCO.
If you’re interested and want to learn more about LINBIT HA, come to the webpage and download a demo or request a quote today.