Adds a "Slot start" log to the LC that behaves similar to BN to inform
the user that the light client is doing something, and to indicate the
latest view of the network (finalized / optimistic).
The `eth1_monitor` check to require engine API from bellatrix onward
has issues in setups where the EL and CL are started simultaneously
because the EL may not be ready to answer requests by the time that the
check is performed. This can be observed, e.g., on Raspberry Pi 4 when
using Besu as the EL client. Now that the merge transition happened, the
check is also not that useful anymore, as users have other ways to know
that their setup is not working correctly (e.g., repeated exchange logs)
The optimistic candidate block check that only imports a new block into
the EL client if its parent block also had execution enabled is not
needed anymore, as mainnet has merged and the attack period is over.
Port changes to `nextExchangeTransitionConfiguration` from BN to LC:
- 60 seconds delay before initial exchange
- 45 seconds interval between followup exchanges
- Only exchange post Bellatrix
When the BN-embedded LC makes sync progress, pass the corresponding
execution block hash to the EL via `engine_forkchoiceUpdatedV1`.
This allows the EL to sync to wall slot while the chain DAG is behind.
Renamed `--light-client` to `--sync-light-client` for clarity, and
`--light-client-trusted-block-root` to `--trusted-block-root` for
consistency with `nimbus_light_client`.
Note that this does not work well in practice at this time:
- Geth sticks to the optimistic sync:
"Ignoring payload while snap syncing" (when passing the LC head)
"Forkchoice requested unknown head" (when updating to LC head)
- Nethermind syncs to LC head but does not report ancestors as VALID,
so the main forward sync is still stuck in optimistic mode:
"Pre-pivot block, ignored and returned Syncing"
To aid EL client teams in fixing those issues, having this available
as a hidden option is still useful.
The optimistic sync spec was updated since the LC based optsync module
was introduced. It is no longer necessary to wait for the justified
checkpoint to have execution enabled; instead, any block is okay to be
optimistically imported to the EL client, as long as its parent block
has execution enabled. Complex syncing logic has been removed, and the
LC optsync module will now follow gossip directly, reducing the latency
when using this module. Note that because this is now based on gossip
instead of using sync manager / request manager, that individual blocks
may be missed. However, EL clients should recover from this by fetching
missing blocks themselves.
* Use final `v1` version for light client protocols
* Unhide LC data collection options
* Default enable LC data serving
* rm unneeded import
* Connect to EL on startup
* Add docs for LC based EL sync
The light client sync protocol employs heuristics to ensure it does not
become stuck during non-finality or low sync committee participation.
These can enable use cases that prefer availability of recent data
over security. For our syncing use case, though, security is preferred.
An option is added to light client processor to configure this tradeoff.
Adds the `--web3-url` launch argument to `nimbus_light_client` to enable
driving the EL with the optimistic head obtained from LC sync protocol.
This will keep issuing `newPayload` / `forkChoiceUpdated` requests for
new blocks, marking them as optimistic. `ZERO_HASH` is reported as the
finalized block for now.
Introduces a new library for syncing using libp2p based light client
sync protocol, and adds a new `nimbus_light_client` executable that uses
this library for syncing. The new executable emits log messages when
new beacon block headers are received, and is integrated into testing.
Etan Kissling
zah
Eugene Kabanov