[feat]: Upgrade RTL to 0.15.5 and add Boltz Service

[kilrau]

Prerequisites

• I have searched for existing issues that already suggest this feature.

Describe the Feature Request

We worked with the RTL team to release https://github.com/Ride-The-Lightning/RTL/releases/tag/v0.15.5, which has a couple of important fixes for the native Boltz swap integration (works for CLN and LND). Upgrading RTL to 0.15.5 only makes sense if Boltz swap service is available, so suggesting to add it.

Describe the Use Case

Boltz is a service that allows Lightning node operators to conveniently rebalance their channels.

Describe Preferred Solution

No response

Describe Alternatives

No response

Anything else?

No response

[Dominion5254]

This is a desirable feature that has come up a handful of times in the past. This will almost certainly be added to the the RTL package for StartOS 040.

[Dominion5254]

@kilrau If I understand correctly, the boltz integration would require a client such as this?

If so, this client would likely have to be packaged as a separate service on StartOS rather than including it in the RTL package

[kilrau]

@kilrau If I understand correctly, the boltz integration would require a client such as this?

If so, this client would likely have to be packaged as a separate service on StartOS rather than including it in the RTL package

Correct, it does. Not sure as to why it has to be packaged separately. It doesn't bring its own UI (that's what RTL is).

[Dominion5254]

boltz-client doesn't necessarily have to be packaged separately but modularity and flexibility would be the primary reasons to keep the boltz-client and RTL separate. Please correct me if I am mistaken, but to my understanding boltz-client can interact directly with LND/CLN via CLI; RTL is not strictly required.

This separation of concerns also helps keep the package size smaller for users who might want RTL but not boltz-client and vice versa (granted, boltz-client isn't particularly large, so this is perhaps less of an concern).

The StartOS dependency management system would allow packaging boltz-client as a stand alone service that requires LND and/or CLN with an optional dependency on RTL.

But if I am mistaken and the used case of boltz-client without RTL is limited, it might make more sense to include both together in a single package.

[kilrau]

You are right. Standalone Boltz Client can only be used via CLI. If there is a way to expose the CLI then it absolutely makes sense.