A library, not a black box
The Lightning Development Kit (LDK) takes a fundamentally different approach from something like LND. LND is a complete, standalone Lightning node you run as a service and talk to over an RPC interface. LDK is a library you embed directly into your own application, and it deliberately leaves you in control of networking, persistence, and key management, providing the protocol logic, channel state machine, and routing algorithms as composable Rust components instead of a monolithic daemon. This tradeoff matters: running LND means adopting its opinions about how a node operates, while embedding LDK means writing more integration code yourself in exchange for a Lightning node that's shaped exactly like your product, whether that's a mobile wallet, a point-of-sale system, or custom infrastructure.
LDK handles the genuinely hard, protocol-correctness-critical parts for you: BOLT-compliant channel establishment, updating channel state as HTLCs (Hash Time-Locked Contracts) are added and settled, and generating the exact messages needed to keep both sides of a channel in sync. Getting any of this wrong risks fund loss or being unable to close a channel correctly, which is precisely the kind of logic you want built and audited once by a shared library rather than reimplemented per project.