Initialize L1 Safe and Finalized head in SyncStatus at OpNode startup

[Kourin1996]

Closes https://github.com/celo-org/celo-blockchain-planning/issues/940

This PR adds code to retrieve and initialize L1 Safe and Finalized head in SyncStatus when OpNode starts, preventing Sequencer from failing to fetch the next L1 finalized block if --sequencer.use-finalized is enabled.

[piersy]

That should be 6.4 minutes I think. An epoch is 32*12 seconds, which is the default for the L1EpochPollIntervalFlag

[palango]

Do we have understanding what blocks the node from fixing itself, i.e. getting an up-to-date L1 finalized reference when the node ran out of the seq drift window?

[Kourin1996]

Do we have understanding what blocks the node from fixing itself, i.e. getting an up-to-date L1 finalized reference when the node ran out of the seq drift window?

@palango As far as I see the code, there's no way to recover the sequencing except for admin API.

FYR, someone raised a similar issue.
ethereum-optimism/developers#701

[seolaoh]

I'm wondering if it's better to consolidate the L1 block fetching logic in one place. Specifically, modifying this code block so that we call fetchAndSignal function immediately before waiting for the first ticker signal.

		fetchAndSignal := func() {
			reqCtx, reqCancel := context.WithTimeout(eventsCtx, timeout)
			ref, err := src.L1BlockRefByLabel(reqCtx, label)
			reqCancel()
			if err != nil {
				log.Warn("failed to poll L1 block", "label", label, "err", err)
			} else {
				fn(eventsCtx, ref)
			}
		}
		fetchAndSignal()

		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for {
			select {
			case <-ticker.C:
				fetchAndSignal()
			case <-eventsCtx.Done():
				return nil
			}
		}

[Kourin1996]

I'm wondering if it's better to consolidate the L1 block fetching logic in one place. Specifically, modifying this code block so that we call fetchAndSignal function immediately before waiting for the first ticker signal.

@seolaoh Generally speaking, I think it will be better in terms of cleanliness, too. However, the value is set only after l2Driver is initialized (inside initL2), which happens after polling is set up (inside initL1). I could add some delays in the polling function, but I think the original approach ensures that the finalized head is fetched and set properly.

func (n *OpNode) OnNewL1Finalized(ctx context.Context, sig eth.L1BlockRef) {
	if n.l2Driver == nil {
		return
	}
	// Pass on the event to the L2 Engine
	ctx, cancel := context.WithTimeout(ctx, time.Second*10)
	defer cancel()
	if err := n.l2Driver.OnL1Finalized(ctx, sig); err != nil {
		n.log.Warn("failed to notify engine driver of L1 finalized block change", "err", err)
	}
}

[seolaoh]

I'm wondering if it's better to consolidate the L1 block fetching logic in one place. Specifically, modifying this code block so that we call fetchAndSignal function immediately before waiting for the first ticker signal.

@seolaoh Generally speaking, I think it will be better in terms of cleanliness, too. However, the value is set only after l2Driver is initialized (inside initL2), which happens after polling is set up (inside initL1). I could add some delays in the polling function, but I think the original approach ensures that the finalized head is fetched and set properly.

func (n *OpNode) OnNewL1Finalized(ctx context.Context, sig eth.L1BlockRef) {
	if n.l2Driver == nil {
		return
	}
	// Pass on the event to the L2 Engine
	ctx, cancel := context.WithTimeout(ctx, time.Second*10)
	defer cancel()
	if err := n.l2Driver.OnL1Finalized(ctx, sig); err != nil {
		n.log.Warn("failed to notify engine driver of L1 finalized block change", "err", err)
	}
}

Oh I didn't know that, then the original approach seems solid to set the finalized head.

[piersy]

Hi @Kourin1996. At present this looks like the best we can do without significant further investigation. But I would say that this does not close the linked issue, since the underlying problem (that the node stalls permanently when maxSequencerDrift is exceeded) remains. So lets merge this but keep the referenced ticket open.