* Rework Validator Client fallback mechanism
* Add CI workflow for fallback simulator
* Tie-break with sync distance for non-synced nodes
* Fix simulator
* Cleanup unused code
* More improvements
* Add IsOptimistic enum for readability
* Use configurable sync distance tiers
* Fix tests
* Combine status and health and improve logging
* Fix nodes not being marked as available
* Fix simulator
* Fix tests again
* Increase fallback simulator tolerance
* Add http api endpoint
* Fix todos and tests
* Update simulator
* Merge branch 'unstable' into vc-fallback
* Add suggestions
* Add id to ui endpoint
* Remove unnecessary clones
* Formatting
* Merge branch 'unstable' into vc-fallback
* Merge branch 'unstable' into vc-fallback
* Fix flag tests
* Merge branch 'unstable' into vc-fallback
* Merge branch 'unstable' into vc-fallback
* Fix conflicts
* Merge branch 'unstable' into vc-fallback
* Remove unnecessary pubs
* Simplify `compute_distance_tier` and reduce notifier awaits
* Use the more descriptive `user_index` instead of `id`
* Combine sync distance tolerance flags into one
* Merge branch 'unstable' into vc-fallback
* Merge branch 'unstable' into vc-fallback
* wip
* Use new simulator from unstable
* Fix cli text
* Remove leftover files
* Remove old commented code
* Merge branch 'unstable' into vc-fallback
* Update cli text
* Silence candidate errors when pre-genesis
* Merge branch 'unstable' into vc-fallback
* Merge branch 'unstable' into vc-fallback
* Retry on failure
* Merge branch 'unstable' into vc-fallback
* Merge branch 'unstable' into vc-fallback
* Remove disable_run_on_all
* Remove unused error variant
* Fix out of date comment
* Merge branch 'unstable' into vc-fallback
* Remove unnecessary as_u64
* Remove more out of date comments
* Use tokio RwLock and remove parking_lot
* Merge branch 'unstable' into vc-fallback
* Formatting
* Ensure nodes are still added to total when not available
* Allow VC to detect when BN comes online
* Fix ui endpoint
* Don't have block_service as an Option
* Merge branch 'unstable' into vc-fallback
* Clean up lifetimes and futures
* Revert "Don't have block_service as an Option"
This reverts commit b5445a09e9.
* Merge branch 'unstable' into vc-fallback
* Merge branch 'unstable' into vc-fallback
* Improve rwlock sanitation using clones
* Merge branch 'unstable' into vc-fallback
* Drop read lock immediately by cloning the vec.
## Issue Addressed
Closes https://github.com/sigp/lighthouse/issues/4291, part of #3613.
## Proposed Changes
- Implement the `el_offline` field on `/eth/v1/node/syncing`. We set `el_offline=true` if:
- The EL's internal status is `Offline` or `AuthFailed`, _or_
- The most recent call to `newPayload` resulted in an error (more on this in a moment).
- Use the `el_offline` field in the VC to mark nodes with offline ELs as _unsynced_. These nodes will still be used, but only after synced nodes.
- Overhaul the usage of `RequireSynced` so that `::No` is used almost everywhere. The `--allow-unsynced` flag was broken and had the opposite effect to intended, so it has been deprecated.
- Add tests for the EL being offline on the upcheck call, and being offline due to the newPayload check.
## Why track `newPayload` errors?
Tracking the EL's online/offline status is too coarse-grained to be useful in practice, because:
- If the EL is timing out to some calls, it's unlikely to timeout on the `upcheck` call, which is _just_ `eth_syncing`. Every failed call is followed by an upcheck [here](693886b941/beacon_node/execution_layer/src/engines.rs (L372-L380)), which would have the effect of masking the failure and keeping the status _online_.
- The `newPayload` call is the most likely to time out. It's the call in which ELs tend to do most of their work (often 1-2 seconds), with `forkchoiceUpdated` usually returning much faster (<50ms).
- If `newPayload` is failing consistently (e.g. timing out) then this is a good indication that either the node's EL is in trouble, or the network as a whole is. In the first case validator clients _should_ prefer other BNs if they have one available. In the second case, all of their BNs will likely report `el_offline` and they'll just have to proceed with trying to use them.
## Additional Changes
- Add utility method `ForkName::latest` which is quite convenient for test writing, but probably other things too.
- Delete some stale comments from when we used to support multiple execution nodes.
## Issue Addressed
NA
## Proposed Changes
- Removes a duplicated log in the fallback code for the VC.
- Updates the text in the remaining de-duped log.
## Additional Info
Example
```
Dec 23 05:19:54.003 WARN Beacon node is syncing endpoint: http://xxxx:5052/, head_slot: 88224, sync_distance: 161774
Dec 23 05:19:54.003 WARN Beacon node is not synced endpoint: http://xxxxx:5052/
```
## Issue Addressed
- Resolves#1883
## Proposed Changes
This follows on from @blacktemplar's work in #2018.
- Allows the VC to connect to multiple BN for redundancy.
- Update the simulator so some nodes always need to rely on their fallback.
- Adds some extra deprecation warnings for `--eth1-endpoint`
- Pass `SignatureBytes` as a reference instead of by value.
## Additional Info
NA
Co-authored-by: blacktemplar <blacktemplar@a1.net>
