A Directive and Implementation Steps:

Directive & Implementation Steps

Directive: steps

… and filling in some steps …

Directive & Two Labelled Steps

Now at this point there seems to be a plan, and at least the first couple of implementation steps.

What unfortunately can happen in moving from Directive to Steps, is that, the overall goal can become less visible.

So we rush ahead and implement the steps, and provided the steps are ticked off, we might think the job is done.

It is easy to implement a load balancer – they are available from many providers who are effectively reselling you a Zeus / Riverbed “Application Delivery Controller” or similar.

The Application Delivery Controller (ADC) will do a job, but it is only as intelligent as the configuration you ask for.

“But if I buy a Layer 7 rather than a Layer 4 then that is better right?”

It depends on what you want – revisit your goal (at the top) and try to avoid being distracted by sales pitches and technobabble.

If your goal is mostly to have High Availability (HA) for http, then you might well be able to ignore the extra features a Layer 7 sales bod might be trying to sell.

Do you really need ftp to be distributed by a load balancer? … you decide.

There is an overview of a few of the common algorithms in the short article here

I include an extract below:

  1. Round Robin
  2. Weighted Round Robin
  3. Least Connections
  4. Least Response Time

It is easy to make the wrong choice from the above, and miss your original directive.

I repeat (and expand) the original directive next

High Availability under all circumstances

That goal is very different than “High Availability under normal circumstances”

An infrastructure / network consultant can help you design for each.

My personal feeling (based in part on experience) is that option 4, “Least Response Time”, might help you achieve a goal of “High availability under normal circumstances”, however it might actually hinder you, if your goal is “High availability under all circumstances”

A reminder about the main point of this article – focus on the original goal.

Implementing an individual step (load balancer), might make you feel like you are moving towards your goal through action, but do keep revisiting your original directive to make sure.

If you do decide to use an infrastructure / network consultant, then have a quick read of commonly available industry solutions here ahead of the consultant session.

Another link which has brief descriptions of Layer 4 and Layer 7 here