Redundancy in System Design

Redundancy is defined as a concept where certain entities are duplicated with aim to scale up the system and reduce over all down-time. 

For example, as seen in the image below, we are duplicating the server. So if one server goes down, then we have a redundant server in our system to balance the load.

Now from the above image, you must be wondering how these connections are handled meaning how to get all load over to another and not let to connect to server/s that are already down. Here we introduce a new term known as the load balancer. 

Load Balancer

A load balancer works as a “traffic cop” sitting in front of your server and routing client requests across all servers. It simply distributes the set of requested operations (database write requests, cache queries) effectively across multiple servers and ensures that no single server bears too many requests that lead to degrading the overall performance of the application. A load balancer can be a physical device or a virtualized instance running on specialized hardware or a software process. 
Consider a scenario where an application is running on a single server and the client connects to that server directly without load balancing. It will look something like the one below.

How to handle the unavailability of a Load Balancer?

If the load balancer becomes unavailable, then the corresponding server will become unavailable and the system will go into downtime. In order to handle such cases, we do opt for two techniques:

1. Way 1: Using backup load balancer technique: It contains primary and secondary load balancers involving concepts of ‘floating ID’ and ‘Health check’.  
2. Way 2: Using DNS Server: For now newbies to understand associate this works quite similar to the redundancy principle.

Note: Geeks do remember that DNS does not keep track of  whether load balancer is working so do we introduce Monitor  to keep track in case of DNS. 

Tip: In system designing failures are inevitable, we could not eliminate them completely can only  work in minimizing them. 

While considering the availability factor while designing systems is directly proportional to geographic location. For instance: For a corresponding service if a system goes down in a particular location (be India) the whole service is available at some other location to make the service operational. In the real world, we are having the complete hardware available across various locations so as not to hamper service at any cost.    

System Design is the core concept behind the design of any distributed systems. System Design is defined as a process of creating an architecture for different components, interfaces, and modules of the system and providing corresponding data helpful in implementing such elements in systems.

In this article, we’ll cover the standard terms and key concepts of system design and performance, such as:

• Latency, 
• Throughput, 
• Availability,
• Redundancy,
• Time
• CAP Theorem
• Lamport’s Logical Clock Theorem.

Let us see them one by one.