d.- Architectural Keys: The interface between different systems is architecture
An overview to help you consolidate the required needs and better serve them with existing systems implies an appropriate approach for future performance and sizing of the portal.
Can use other tools such as Apache Solr to handle searches and filters is a decision that allows our portals to perform at a level better than with the structure of Drupal search.
Delegate to other products and use the modules as containers for configuration information and is a successful approach already followed by Drupal, from the famous Jquery to other modules that allow you to use products or services in order to realize their functionality.
Acquia offers Solr Apache as a service, for example.
It is one of many ways to combine efforts and see the success of the system as a relationship.
So make a good architecture is about making a good relationship with the possibilities of each moment and be aware that the state of the art is constantly changing these relations, which is directly related to the current version of Drupal and any other improvements in other components decant that our architecture can become obsolete.
That is why an ongoing study of the state of the art systems is essential for proper architectural approach with Drupal.