LXD is a modern, secure system container and virtual machine manager developed by Canonical. It provides a REST API over a Unix socket and HTTPS, a command-line client (lxc), and an in-guest agent (lxd-agent). The architecture is a monolithic daemon with pluggable storage drivers (ZFS, Btrfs, LVM, Ceph, dir, and enterprise SAN), network drivers (bridge, OVN, macvlan, SR-IOV, physical), and device passthrough (GPU, USB, NIC, TPM, proxy). It supports clustering via dqlite/Raft for high availability, fine-grained authorization via OpenFGA, OIDC authentication, and ACME certificate provisioning. The codebase is written in Go with CGo for low-level Linux operations (namespaces, seccomp, AppArmor, cgroups) and includes extensive unit and integration tests. Key features include live migration, incremental backups, cloud-init integration, and a built-in metrics endpoint for Prometheus.