Although all of us like reading online, I still prefer having a printed book versions in my home office library. You can find a list of the books which I own and recommend here. Feel free to reach out to me and suggest some technical books which I should read.
Systems Performance: Enterprise and the Cloud by Brendan Gregg
Jenkins 2: Up and Running by Brent Laster
The Practice of System and Network Administration: Volume 1: DevOps and other Best Practices for Enterprise IT by A. Limoncelli, Christina J. Hogan, Strata R. Chalup