A pattern is simply a template that can be applied to solve a specific set of problems. As you can imagine, a pattern is simply a blueprint of what could be done. It is up to the implementer to apply and implement the pattern.

We can also think of architectural patterns slightly differently. When we observe something in our current architecture that we believe can be reused elsewhere, we extract that out and capture the design ideas as an archetype. The design patterns are always, or should always be, technology-independent. If a pattern can only be implemented using a specific technology, it usually is not a pattern but just a technology-specific problem.

The following is not an exhaustive list of architectural patterns, but a collection of patterns and traits of existing systems that are successfully designed following the Architectural Principles we defined in earlier chapters.

Let's start discussing these patterns in a little detail.