[EPIC] [EFM Recovery - M3] Overview

[AlexHentschel]

Broad system-level overview

The following is an overview of which components control the Epoch Fallback Mode [EFM] and which components react to it (all prior to any work on EFM Recovery). Those will probable be the components where the central algorithmic changes will be made.

👉 Design Document in Notion

Components controll EFM mode

The FollowerState (mutator) / ParticipantState implements

• logic for emitting the EpochEmergencyFallbackTriggered notification.
• sets a corresponding flag in the data base

Components that ingest EpochEmergencyFallbackTriggered notification (in-memory)

• committees.Consensus
• BlockTimeController
• EpochLookup
• Metrics: ComplianceCollector and the respective interface ComplianceMetrics
• Pub-sub components for distributing notifications: events.Distributor and corresponding interface protocol.Consumer

Components that read EpochEmergencyFallbackTriggered flag from data base

• InstanceParams reads the flag from data base on each call of EpochFallbackTriggered()
• The protocol State reads the flag from data base when updating the metrics during bootstrapping or opening the state
• The FollowerState (mutator) / ParticipantState reads the flag from data base when finalizing a new block

### Tasks
- [ ] https://github.com/onflow/flow-go/issues/5762
- [ ] https://github.com/onflow/flow-go/issues/5127
- [ ] https://github.com/onflow/flow-go/issues/5723
- [ ] https://github.com/onflow/flow-go/issues/5725
- [ ] https://github.com/onflow/flow-go/issues/5728
- [ ] https://github.com/onflow/flow-go/issues/5631
- [ ] https://github.com/onflow/flow-go/issues/5727
- [ ] https://github.com/onflow/flow-go/issues/5726
- [ ] https://github.com/onflow/flow-go/issues/5724
- [ ] https://github.com/onflow/flow-go/issues/5717