Rollups = Bridges + Blockchains

[bruno_f]

@JonCharbonneau

Was admittedly slightly afraid when I saw the title .

The title is a tad click-baity, I agree.

@JonCharbonneau

Could you elaborate here? I don’t think I would agree with this if I’m understanding your argument correctly. As described in the post, a “sovereign” rollup (i.e., no bridge) can still inherit the technical security of its base layer, so it’s not only for the benefit of the bridge. Also as described in this great thread by @sreeramkannan.

Sovereign rollups do indeed inherit the security of the base chain. In that paragraph I’m excluding them, and my point is that I don’t consider sovereign rollups to be rollups at all. Looking at all different constructions that are talked about, it seems like there are two independent properties: 1) having a trust-minimized bridge, 2) piggybacking/depending/co-opting the base chain’s consensus.
We can imagine a 2-by-2 table with these properties:

• Has a bridge + co-opts consensus: This would be Based Rollups, for example, and other constructions like it.
• Has a bridge + independent consensus: Basically every rollup that exists today, having a centralized server is basically a separate chain. Also in this category, rollups that plan to decentralize by implementing their own PoS chain. The example I gave of Ethereum and Near connecting through a trust minimized bridge would also fit in here.
• No bridge + co-opts consensus: Sovereign “rollups” fit in here.
• No bridge + independent consensus: These are simply two separate blockchains/L1s. Nothing special here.

For me, it seems weird to consider everything that isn’t separate L1s as rollups. Going back to the example I gave of connecting Ethereum and Near through trust-minimized bridges, if we consider that construction a rollup (and I think we should), then it’s somewhat jarring to also consider sovereign rollups as rollups.

@JonCharbonneau

I don’t believe this is true? You either need to embed a base layer full node within the rollup full node or have the ability to run a trust-minimized light client (eg, with DAS). If you were to launch a sovereign rollup on Ethereum today, you would then need to embed an Ethereum full node in the rollup full node. However, that’s due to current base layer implementation, not fundamental to sovereign rollups (and can change in the future for Ethereum).

That’s interesting actually, I haven’t thought of that. Although, if every rollup full node just has a light-client to the base chain, then they would need to be continually asking base chain full nodes for relevant transactions. Not very practical but probably works. But fair enough, it is another type of bridge then, light client bridge, and sovereign “rollups” could indeed work with it. With DAS and validity proofs it could be a very interesting light client bridge.

@JonCharbonneau

This is a very interesting area! Actually reminds me quite a bit of what Anatoly had tweeted about recently as described here. Also an idea for a “trust-minimized” bridge between two chains without being a “rollup” necessarily, where the bridge could again fork away. Still need to think more about this/potential issues.

What Anatoly describes is basically an “escape hatch” mechanism. It’s not that different from what most rollups are implementing currently. But I would say that if you have a trust-minimized bridge between two chains then it is a rollup.

@JonCharbonneau

Just curious what you disagree on, always fun to chat on

I’m not sure I want to derail this topic that much! It’s probably already going to be a long discussion as it is. But you can DM me if you like and I’ll be happy to share my opinions on shared sequencers too.

@JonCharbonneau

This is a great post and really enjoyed reading it, thanks again for the thoughtful response!

Thanks! I like reading your posts too, so it’s nice to be able to contribute back.