In my previous post, I reviewed the 5 Infrastructure Characteristics that will be included as a part of a good design. The framework is layed out in the great work IT Architect: Foundations in the Art of Infrastructure Design. In this post, I’m going to continue that theme by outlining the 4 Considerations that will also be a part of that design.


While the Characteristics could also be called “qualities” and can be understood as a list of ways by which the design can be measured or described, Considerations could be viewed as the box that defines the boundaries of the design. Considerations set things like the limits and scope of the design, as well as explain what the architect or design team will need to be true of the environment in order to complete the design.


Design Considerations

I like to think of the four considerations as the four walls that create the box that the design lives in. When I accurately define the four different walls, the design to go inside of it is much easier to construct. There are less “unknowns” and I leave myself less exposed to faults or holes in the design.


Requirements – Although they’re all very important, I would venture to say that Requirements is the most important consideration. “Requirements”is  a list - either identified directly by the customer/business or teased out by the architect – of things that must be true about the delivered infrastructure. Some examples listed in the book are a particular Service Level Agreement metric that must be met (like uptime or performance) or governance or regulatory compliance requirements. Other examples I’ve seen could be usability/manageability requirements dictating how the system(s) will be interfaced with or a requirement that a certain level of redundancy must be maintained. For example, the configuration must allow for N+1, even during maintenance.


Constraints – Constraints are the considerations that determine how much liberty the architect has during the design process. Some projects have very little in the way of constraints, while others are extremely narrow in scope once all of the constraints have been accounted for. Examples of constraints from the book include budgetary constraints or the political/strategic choice to use a certain vendor regardless of other technically possible options. More examples that I’ve seen in the field include environmental considerations like “the environment is frequently dusty and the hardware must be able to tolerate poor environmentals” and human resource constraints like “it must be able to be managed by a staff of two.”


Risks – Risks are the architect’s tool for vetting a design ahead of time and showing the customer/business the potential technical shortcomings of the design imposed by the constraints. It also allows the architect to show the impact of certain possibilities outside the control of either the architect or the business. A technical risk could be that N+1 redundancy actually cannot be maintained during maintenance due to budgetary constraints. In this case, the risk is that a node fails during maintenance and puts the system into a degraded (and vulnerable) state. A risk that is less technical might be something like that the business is located within a few hundred yards of a river and flooding could cause a complete loss of the primary data center. When risks are purposely not mitigated in the design, listing them shows that the architect thought through the scenario, but due to cost, complexity, or some other business justification, the choice has been made to accept the risk.


Assumptions – For lack of a better term, an assumption is a C.Y.A. statement. Listing assumptions in a design shows the customer/business that the architect has identified a certain component of the big picture that will come into play but is not specifically addressed in the design (or is not technical in nature). A fantastic example listed in the book is an assumption that DNS infrastructure is available and functioning. I’m not sure if you’ve tried to do a VMware deployment recently, but pretty much everything beyond ESXi will fail miserably if DNS isn’t properly functioning. Although a design may not include specifications for building a functioning DNS infrastructure, it will certainly be necessary for many deployments. Calling it out here ensures that it is taken care of in advance (or in the worst case, the architect doesn’t look like a goofball when it isn’t available during the install!).


If you work these four Considerations (and the 5 Characteristics I detailed in my previous post) into any design documentation you’re putting together, you’re sure to have a much more impressive design. Also, if you’re interested in working toward design-focused certifications, many of these topics will come into play. Specifically, if VMware certification is of interest to you, VCIX/VCDX work will absolutely involve learning these factors well. Good luck on your future designs!