Difference between Cluster module and load balancer

Load balancing distributes the workload amongst multiple servers to improve the performances meanwhile server clustering, combines multiple servers to work as a single entity.

Cluster module or Clustering: A cluster is a group of resources that attempts to achieve a common objective, and have awareness of one another within the group. Each container, server, or virtual server within a cluster is called a node. Clustering generally involves setting up the resources (servers usually) to exchange specifications on a particular channel and keep exchanging their states, that is when the resource’s state is replicated at other places as well. For example, many servers can be connected together to appear as a single server and share one single IP address.  

The cluster module usually supports two methodologies of distributing incoming connections. The round-robin approach, where the primary process listens on an incoming port, accepts new connections, and later distributes them across the workers in a round-robin manner, with some built-in techniques to avoid overloading a worker process. Another way is where the primary process creates the listen sockets and later sends them to interested workers. The workers later accept incoming connections directly.

The most basic clusters use a pair of redundant servers. More advanced clusters contain many other different machines, each connected and exchanging information about states and other resources. While it is technically possible for clusters to contain different types of nodes but performance reduces if the nodes are not identical.  Some of the clusters available are High Availability Server Clusters, Load Balancing Clusters, High-Performance Clusters, and Storage Clusters.

Load Balancer: A load balancer is a technology that takes in all HTTP requests and forwards these HTTP requests to one of a collection of servers. Load balancing seeks to avoid overstressing any one single device by splitting up the jobs or traffic flow. We can use a load balancer to proceed requests to either one server or other, but one server does not use the resources of the other servers. Also, one resource doesn’t share its state with other resources. Each load balancer basically does tasks like continuously checking which servers are up.  Load balancers can be simple or sophisticated. Simple load balancers generally consist of DNS Round Robin and an OSI Layer 3/Layer 4 (L3/L4) load balancers that work at the TCP and IP layers. More sophisticated load balancers generally distribute work based upon application data (OSI Layer 7)

When a new request is received, send it to one of the servers according to the load balancing policy. While a request is received for a user who already has a session ahead, send the user to the very same server (to prevent the user from going to different servers and not being able to really do any work). There are plenty of powerful load balancing tools out there, like Nginx or HAProxy.

Similarities between Cluster Module and Load Balancer: Both technologies have several characteristics in common:

• To any external device, both technology usually appears to be a single machine that manages all of the requests.
• Both of them often incorporate reverse-proxy technologies that allow a single IP address to redirect traffic to different IP or MAC addresses.
• Both technologies are developed for managing a data center’s physical servers but have later been extended to applications, creating virtual servers, cloud servers, and container technology.

Difference between Cluster module and load balancer:

Load Balancers	Cluster Module
Load Balancers distribute the processing load among the group of servers.	A cluster is a group of servers that run as if it were a single entity.
Load balancing can be more simple to deploy with different types of servers	It usually requires identical servers within the cluster
Load balancers require additional networking expertise for managing the different types of connected servers	Server clusters are more self-contained and managed by a controller automatically
Load balancers can operate independently of the destination servers and thus consumes fewer resources.	Cluster modules require node managers and node agents to communicate within the cluster which occupies bandwidth and processing on the servers
Relatively less resilient Load Balancing for applications eg.-While doing transactions If one server fails, the customer has to re-enter data again from the start as the user state will be lost.	Server clusters are more resilient for applications eg.-If any server got failed during the transaction, another server within the cluster will work and the customer will complete the transaction.