- Systems Performance by Brendan Gregg
- BPF Performance Tools by Brendan Gregg
- Site Reliability Engineering by Betsy Beyer, Chris Jones, Jennifer Petoff and Niall Murphy
- Building Secure and Reliable Systems edited by Heather Adkins, Betsy Beyer, Paul Blankinship, Piotr Lewandowski, Ana Opera and Adam Stubblefield
- The Site Reliability Workbook edited by Betsy Beyer, Niall Richard Murphy, David K. Rensin, Kent Kawahara and Stephen Thorne
- Designing Data-Intensive Applications by Martin Kleppmann
- High Performance MySQL: Optimization, Backups and Replication by Baron Schwartz, Peter Zaitsev and Vadim Tkachenko
- BGP: Building Reliable Networks with the Border Gateway Protocol by Iljitsch van Beijnum
- TCP/IP Guide: A Comprehensive, Illustrated Internet Protocols Reference by Charles M. Kozierok
- Kubernetes: Up and Running by Kelsey Hightower, Bredan Burns and Joe Beda
- Brendan Gregg's Blog - good explanations of low-level systems performance insights and observability techniques and fundamentals
- Julia Evans' Blog and associated zines - good breakdowns of low-level systems concepts and an emphasis on protocols
- CNCF (Cloud Native Computing Foundation) Project Blog Posts - warning: this has a lot of content, but is good for getting a view into updates across the broad surface area which is the CNCF landscape
- Linux Insides - this is a super detailed resource which covers linux internals in a great deal of depth
- System Design Primer
- Kubernetes the Hard Way
- Awesome MySQL
- Awesome Postgres