Sequencer plugin to send a L2 pausing tx when sequencer hasn't produced block recently

[julien-marchand]

Description

Extend the sequencer plugin to send an L2 tx if the last block produced is older than X seconds.

Motivation

This should allow Aave and other protocols to have a smoother approach to liquidations if the sequencer hasn't been producing any block recently and prices haven't been able to be updated.

Architecture

• No impact on the architecture. This should sit in the existing sequencer plugin.

Implementation guidelines

• When building a block, if the last block produced is more than X seconds old, add a first transaction to the block that calls the SequencerUptimeFeed contract
  • LineaSequencerUptimeFeed.updateStatus(false, lastBlockTimestamp)
  • LineaSequencerUptimeFeed.updateStatus(true, currentTimestamp)
• The added transaction shouldn't be subject to gas price checks
• Transaction signature should be done using Web3Signer
• Add e2e tests to cover this
• This feature should be optional

Metrics/monitoring

• What needs to be monitored once this epic has been shipped?

Rollout

• Create Web3Signer account and have it configured on the contract
• Deploy the contracts
• Add/configure plugin on the sequencer

Infrastructure & Node operators

• No impact expected

Documentation & communication

• Communicate to Aave and Chainlink that this feature is available.