In Bootstrapping shopware: The dispatch loop I show what happens, if a request hits Shopware and how Shopware figures out, which controller should be in charge to answer the request. I think it gives a fairly good overview of some basic Shopware internals.
In The Shopware SEO engine I discuss the internals of Shopware's SEO engine. It will help you not only to understand the details of Shopware implementation and how to extend it; it also gives an impression about how generally flexible SEO engines might be implemented.
In cross cutting concerns I generally discuss various types of "concerns" and especially "cross cutting concerns". This type of concern is usually hard to handle in OOP applications and might lead to duplicated or highly coupled code. I discuss different ways to address cross cutting concerns. As a follow up I also discussed aspect oriented programming as a way to address cross cutting concerns in a separate blog post.
In Understanding the Shopware hook system I discuss the Shopware hook system as one part of the plugin system of Shopware. Hooks are quite powerful and allow aspect oriented programming in PHP, even though PHP do not natively support AOP. In the blog post, also details of the implementation and pros and cons are discussed.
In Understanding the Shopware HTTP cache I give a more detailed overview of Shopware's caching system. It is not only about the general concept of HTTP caches, ESI and cache invalidation, but also about possibilities to influence the default behaviour from a plugin.