feat: implement Nimbus beacon service

[iofq]

Implements Nimbus Beacon service (validator service to follow).

Two things I think could be contentious:

• Using ExecPreStart for the checkpoint sync. Nimbus has this implemented somewhat awkwardly IMO, in that it's a separate command. ExecPreStart has a timeout of 15 mins; in all my testing the checkpoint finished downloading in 2 or 3 mins, but had it not completed before the timeout, the systemd service will fail to start. We can as well adjust that 15 minute timeout to be longer or infinite.

• Opening REST and Metrics ports by default. This seems to be done by default in Lighthouse at least, which i used for reference for a lot of this, however I would argue that the majority of users would not want these exposed and as such maybe it should be a more explicit enable, either within the module or done outside of it. Not sure what the best UX is here.

[brianmcgee]

@iofq thanks for the PR!

I'll have a look start of next week, but a cursory glance looks good.

Using ExecPreStart for the checkpoint sync. Nimbus has this implemented somewhat awkwardly IMO, in that it's a separate command. ExecPreStart has a timeout of 15 mins; in all my testing the checkpoint finished downloading in 2 or 3 mins, but had it not completed before the timeout, the systemd service will fail to start. We can as well adjust that 15 minute timeout to be longer or infinite.

I think leaving the 15 min timeout for now is a good start.

Opening REST and Metrics ports by default. This seems to be done by default in Lighthouse at least, which i used for reference for a lot of this, however I would argue that the majority of users would not want these exposed and as such maybe it should be a more explicit enable, either within the module or done outside of it. Not sure what the best UX is here.

I think the pattern has been to try and mimic what the underlying process does, but I agree that by default exposing the REST interface and metrics could be dangerous. Maybe this approach needs changed throughout all the services.

[iofq]

rebased and signed commit

[brianmcgee]

lgtm