*Disclaimer: None of that is meant as a slight in opposition to any consumer particularly. There’s a excessive chance that every consumer and presumably even the specification has its personal oversights and bugs. Eth2 is a sophisticated protocol, and the individuals implementing it are solely human. The purpose of this text is to spotlight how and why the dangers are mitigated.*
With the launch of the Medalla testnet, individuals had been inspired to experiment with completely different shoppers. And proper from genesis, we noticed why: Nimbus and Lodestar nodes had been unable to deal with the workload of a full testnet and bought caught. [0][1] In consequence, Medalla did not finalise for the primary half hour of its existence.
On the 14th of August, Prysm nodes misplaced monitor of time when one of many time servers they had been utilizing as a reference all of a sudden jumped at some point into the longer term. These nodes then began making blocks and attestations as if they had been additionally sooner or later. When the clocks on these nodes had been corrected (both by updating the consumer, or as a result of the timeserver returned to the right time), people who had disabled the default slashing safety discovered their stakes slashed.
Precisely what occurred is a little more refined, I extremely advocate studying Raul Jordan’s write-up of the incident.
Clock Failure – The enworsening
The second when Prysm nodes began time touring, they made up ~62% of the community. This meant that the edge for finalising blocks (>2/3 on one chain) couldn’t be met. Worse nonetheless, these nodes could not discover the chain that they had been anticipating (there was a 4 hour “hole” within the historical past they usually all jumped forward to barely completely different instances) and they also flooded the community with brief forks as they guessed on the “lacking” knowledge.
Prysm presently makes up 82% of Medalla nodes 
! [ethernodes.org]
At this level, the community was flooded with 1000’s of various guesses at what the top of the chain was and all of the shoppers began to buckle underneath the elevated workload of determining which chain was the correct one. This led to nodes falling behind, needing to sync, operating out of reminiscence, and different types of chaos, all of which worsened the issue.
Finally this was a great factor, because it allowed us to not solely repair the foundation drawback referring to clocks, however to emphasize check the shoppers underneath situation of mass node failure and community load. That stated, this failure needn’t have been so excessive, and the perpetrator on this case was Prysm’s dominance.
Shilling Decentralisation – Half I, it is good for eth2
As I’ve discussed previously, 1/3 is the magic quantity relating to secure, asynchronous BFT algorithms. If greater than 1/3 of validators are offline, epochs can not be finalised. So whereas the chain nonetheless grows, it’s not doable to level to a block and assure that it’ll stay part of the canonical chain.
Shilling Decentralisation – Half II, it is good for you
To the utmost doable extent, validators are incentived to do what is sweet for the community and never merely trusted to do one thing as a result of it’s the proper factor to do.
If greater than 1/3 of nodes are offline, then penalties for the offline nodes begin ramping up. That is known as the inactivity penalty.
Because of this, as a validator, you wish to attempt to make sure that if one thing goes to take your node offline, it’s unlikely to take many different nodes offline on the identical time.
The identical goes for being slashed. Whereas, there’s at all times an opportunity that your validators are slashed attributable to a spec or software program mistake/bug, the penalties for single slashings are “solely” 1 ETH.
Nonetheless, if many validators are slashed similtaneously you, then penalties go as much as as excessive as 32 ETH. The purpose at which this occurs is once more the magic 1/3 threshold. [An explanation of why this is the case can be found here].
These incentives are known as liveness anti-correlation and security anti-correlation respectively, and are very intentional features of eth2’s design. Anti-correlation mechanisms incentivise validators to make choices which can be in the most effective curiosity of the community, by tying particular person penalties to how a lot every validator is impacting the community.
Shilling Decentralisation – Half III, the numbers
Eth2 is being applied by many unbiased groups, every creating unbiased shoppers in response to the specification written primarily by the eth2 analysis staff. This ensures that there are a number of beacon node & validator consumer implementations, every making completely different choices concerning the expertise, languages, optimisations, trade-offs and so forth required to construct an eth2 consumer. This fashion, a bug in any layer of the system will solely affect these operating a particular consumer, and never the entire community.
If, within the instance of the Prysm Medalla time-bug, solely 20% of eth2 nodes had been operating Prysm and 85% of individuals had been on-line, then the inactivity penalty would not have kicked in for Prysm nodes and the issue might have been fastened with solely minor penalties and a few sleepless nights for the devs.
In distinction, as a result of so many individuals had been operating the identical consumer (a lot of whom had disabled slashing safety), someplace between 3500 and 5000 validators had been slashed in a brief time period.* The excessive diploma of correlation signifies that slashings had been ~16 ETH for these validators as a result of they had been utilizing a preferred consumer.
* On the time of writing, slashings are nonetheless pouring in, so there isn’t any last quantity but.
Attempt one thing new
Now’s the time to experiment with completely different shoppers. Discover a consumer {that a} minority of validators are utilizing, (you possibly can take a look at the distribution here). Lighthouse, Teku, Nimbus, and Prysm are all moderately secure in the mean time whereas Lodestar is catching up quick.
Most significantly, TRY A NEW CLIENT! We now have a chance to create a extra wholesome distribution on Medalla in preparation for a decentralised mainnet.
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