What is a server cluster

[Deadly Night Shade]

1. What is a server cluster
2. How are they made

[Oshino Shinobu]

Put simply, a server cluster is just a number of servers that communicate with each other to work together, often used for distributed computing but appearing to an end user as a single system. Clusters can be used to improve performance and/or availability of a service or application compared to that of a single server. The reasons and benefits of using a cluster will change with different situations and use cases. It can often be a case of it simply being more cost effective to have multiple servers working together than a single server of comparable performance.

 

There's multiple ways to create a server cluster. A lot are connected over local networks using readily available networking standards defined by the likes of IEEE, while others may use proprietary connections that are only available within a certain set of systems. 

 

Open Source Cluster Application Resources (OSCAR) is a Linux based software for cluster computing. As the name suggests and as is typical for Linux systems, it is an open source project that anyone can use. 

 

A good start to understanding server clusters is likely Microsoft Cluster Server (MSCS). Microsoft has a page explaining what it is and how it works. 

 

https://technet.microsoft.com/en-us/library/cc738051(v=ws.10).aspx

[Mikensan]

A generalization of a cluster is just that, a group/cluster of computers working towards a common goal. How they are connected to one another changes the "type" of cluster.

 

A couple quick examples you've likely heard of would be a Bot Net or Folding at Home. Both are accomplished by installing software that links computers together, and are issued commands remotely to work together.

 

It takes special configuration and software to actually utilize a cluster, you can't for example take 3 gaming computers, "cluster them" and then play Far cry at 1,000fps. 

[Andster29]

So far everyone has talked about the performance advantage of computer clusters. One of the other advantage of computer clusters is redundancy. The hypervisor software ESXI, allows cluster to work in a redundant environment. 

 

In our production, we have a total of three separate host that all of our servers run on. Each host is running ESXI and run together as a cluster. If one of the host goes down, the other two will pick up exactly where the one that went down left off. I believe currently, all servers will run on a single host and then switch host if the current one faults. 

 

 

[Adyn]

There are two types of server clusters distributed and attached.

 

Distributed clusters take a workload activity (task) and spread it between multiple hosts they generally have control node(s) that allocate the activity and collect and serve up the results. These are typically compute intensive and spread the workload in order to achieve their results. If an individual node does not respond with the work package, then this is served to another node in order to carry out that task.

 

Attached clusters share storage between the nodes (and when I say attached it does not necessarily need to be attached to the devices it can be over a network but then storage area networks (SAN) are networked so the analogy is just for understanding). Attached clusters share access to a common storage medium so guest machines running on the cluster (or guest processes depending on the type) have their activity visible to multiple hosts.

 

As Andster29 pointed out this gives a measure of redundancy as if a physical host fails the other hosts can pick up the workload with only the information running in the physical memory and CPU cache being lost.

 

As for how are they made it really depends on what you are wanting to make to either distribute workload or improve availability in order to answer that and that would be an entirely different question.

[samiscool51]

On 10/24/2016 at 8:36 AM, Deadly Night Shade said:

1. What is a server cluster
2. How are they made

i will be useing windows server as an example

1. a collection of servers in a group and/or domain, many advantages can range from: making 2 copy's of data on two separate servers to keeping important services online even if the main server that was hosting it goes down

2. if the servers are in a domain it's done automatically for you and all you have to do is configure it for your needs, it is possible to do it between two servers on separate domains but i can't remember how it's done and how it works