The first Drupal 8 book on the market was Drupal 8 Configuration Management, by Anja Schirwinski and Stefan Borchert from undpaul in Hannover Germany. Anja is Co-Founder and CEO of undpaul. I ran into her and undpaul's other Co-Founder/CEO, Johannes Haseitl in early May at the re:publica 2015 in Berlin, where I gave a presentation on open source and the economy.
Read the full post and see the conversation video at the Acquia Developer Center: https://dev.acquia.com/podcast/201-drupal-8-configuration-management-we-wrote-book