Built for engineers who operate at cloud scale, this book demystifies Software for Open Networking in the Cloud (SONiC)—the disaggregated network OS powering high-performance, merchant-silicon switches. Using the contemporary SONiC release as its baseline, it speaks to network architects, platform and silicon/SDK engineers, SREs, and hands-on operators who demand predictable performance, vendor neutrality, and operational clarity. From first principles to production playbooks, it shows how modular services compose into a deterministic system and how to navigate the hardware compatibility list alongside real-world platform variance. Grounded in current community drops, it balances architecture with pragmatic guidance. Trace plane separation and table-driven orchestration end to end, then see how intent becomes hardware through the Switch Abstraction Interface (SAI) Configure routing with FRR , design EVPN VXLAN fabrics, and engineer ECMP, MLAG, and BFD for fast convergence. Master QoS and buffering (PFC/ECN), integrate platforms via ONIE and multi-ASIC designs, and understand builds, security hardening, and the Debian 12 base OS. Learn containerized service composition and safe restarts with Docker; decode SONiC’s Redis-backed databases and gNMI telemetry; validate with VS/PTF/sonic-mgmt; and upgrade with warm/fast reboot and rollback. Familiarity with IP networking and Linux is assumed.