Lightning Wallet is mostly autonomous, but does not usually work alone. A special server called Olympus helps it with general maintenance tasks.
Note: the wallet does not depend on or ever shares any personally identifying information with Olympus and is designed to work perfectly fine even when the Olympus server goes offline for an indeterminate periods of time.
Here is what Olympus server does:
It collects and provides an aggregate fiat price for Bitcoin (by periodially polling a number of well-known exchanges), as well as the current Bitcoin transaction fee rates which are taken directly from a local full Bitcoin node. Note: wallet caches this data locally so in case of Olympus going offline fiat prices will likely stay relevant for hours and Bitcoin fees never completely lose their relevance at all.
Maintains a list of public Lightning nodes which the wallet uses to open payment channels. Note: Olympus only provides node information - all payment channel management (including opening and closing of channels) is done entirely by the Lightning Wallet in a completely autonomous manner.
Provides partial payment routes by traversing a graph of available payment channels. This relieves the wallet of some of the burden of maintaining such a graph locally, which may quickly become computationally infeasible for a mobile phone app, however this also introduces privacy implications which need clarifications:
Wallet always asks for a partial route which starts at your peer’s node. This provides a plausible deniability since your peer may have many different wallets connected to it so there is no way for Olympus to tell for sure which exact wallet asks for a route.
Wallet knows when a payment is being sent directly to your peer and does not ask Olympus for a payment route in this special case.
Recipient may insert an assisted route right into it’s payment request and wallet is smart enough to detect and use it. Here is an example: suppose a complete route is
A (you) → B (peer) → C → D → E (payee), in case when payee adds an assisted
D → E route into it’s payment request an Olympus will be asked to provide only
B (peer) → C → D part so it would know neither who is a sender nor who is a receiver here.
Schedules delayed refund Bitcoin transactions, which spend funds from a payment channel to your Bitcoin wallet in a case of a forced channel closing. Note: your wallet is capable of spending these transactions all by itself but it’s possible that you lose your phone before a refund time lock is cleared so Olympus acts as a safety belt here. This service also requires one storage token.