tl;dr - Many people love 2-node clusters because they seem conceptually simpler and 33% cheaper, but while it’s possible to construct good ones, most will have subtle failure modes

The first step towards creating any HA system is to look for and try to eliminate single points of failure, often abbreviated as SPoF.

blockdiag and its family generate diagram images from simple text files:

Features:

Supports many types of diagrams
        block diagram (w/ blockdiag)
        sequence diagram (w/ seqdiag)
        activity diagram (w/ actdiag)
        logical network diagram (w/ nwdiag)

Generates beautiful diagram images from simple text format (similar to graphviz’s DOT format)

Layouts diagram elements automatically

Embeds to many documentations; Sphinx, Trac, Redmine and some wikis

Enjoy documentation with blockdiag !