Yesterday, Ethereum had another bug in one of the consensus clients, called Nimbus, which made them lose sync to the head of the chain. Consensus breaking bugs occur quite often. The last big one was a Prysm bug 2 months ago. Nimbus recent incident meant, that everyone using Nimbus could not attest anymore and the node runners lost some income. But for the network it wasn't really a big issue. Thanks to client diversity, the network did not really struggle in any meaningful way. What is more interesting though is that such an incident can give us insights in how many people use a certain client. Before the incident, attestation participation was at around 99.8% after the incident, the attestation participation dropped to 94.5% within 4 epochs (~25 minutes). Or in other words, it looks like that around 5% of all validators are exclusively using nimbus as the consensus client. This fits very well with the numbers on clientdiversity.org, which has nimbus usage at 4.58%. It is great to see that these estimations on clientdiversity.org are pretty accurate as they are used in discussions about client diversity.

The source of the Nimbus bug are still unknown, but I am sure we will hear about it in the coming days. Fixing the issue is also quite simple, just restart your client. The aftermath of the incident was pretty harmless. Within 3 hours participation was back over 99% and after 9 hours after the incident, participation was still slowly increasing as more and more node operators restarted their clients.

Credits to u/haurog for the write up