The animal on the cover of The Site Reliability Workbook is a green thornytail iguana (Uracentron azureum), an arboreal lizard that lives in the Amazon and other South American rainforests.
The skin of this lizard is a very vivid green, interspersed with black stripes. As its name suggests, it also has rows of spikes on its tail, but the purpose of these is unclear. The green thornytail lizard is rather small, at about 3.5 inches long, and is difficult to spot in the wild because it tends to live high in the forest canopy (where it can more easily bask in sunlight). Ants make up the bulk of the lizard's diet, which it catches by using a "sit and wait" method until insects wander by its location on a tree.
Many of the animals on O'Reilly covers are endangered; all of them are important to the world. To learn more about how you can help, go to animals.oreilly.com.
The cover image is from a loose plate, source unknown. The cover fonts are URW Typewriter and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag's Ubuntu Mono.