97 Things Every Software Architect Should Know

Chapter 41. Engineer in the White Spaces

Michael Nygard wrote Release It! Design and Deploy Production-Ready Software (Pragmatic Bookshelf), which won a Jolt Productivity award in 2008. His other writings can be found at http://www.michaelnygard.com/blog.

—Michael Nygard

A SYSTEM CONSISTS OF INTERDEPENDENT PROGRAMS. We call the arrangement of these programs and their relationships architecture. When we diagram these systems, we often represent individual programs or servers as simplistic little rectangles, connected by arrows.

One little arrow might mean, "Synchronous request/reply using SOAP-XML over HTTP." That's quite a lot of information for one glyph to carry. There's not usually enough room to write all that, so we label the arrow with either "XML over HTTP" from an internal perspective, or "SKU Lookup" for the external perspective.

That arrow bridging programs looks like a direct contact, but it isn't. The white space between the boxes is filled with hardware and software components. This substrate may contain:

Network interface cards Network switches Firewalls IDS and IPS Message queues or brokers XML transformation engines FTP servers

"Landing zone" tables Metro-area SoNET rings MPLS gateways Trunk lines Oceans Cable-finding fishing trawlers

There will always be four or five computers between program A and B, running their software for packet switching, traffic analysis, routing, threat ...