Arbitrum One Outage Report

Beginning at 10:14 AM Eastern today (September 14, 2021) and continuing for approximately 45 minutes, the Arbitrum Sequencer was offline. Funds were never at risk, but the submission of new transactions stopped during the downtime. Arbitrum One is still in its beta phase, and we will do our best to minimize downtime. But, as we noted in our launch announcement, we do want to caution users that further outages are possible in these early days.

All transactions that had been accepted by the Sequencer were included and not re-ordered. Transactions accepted by the Sequencer between 10:13 and 10:14 AM ET were re-assigned a timestamp when the Sequencer returned online at 10:59AM, but the ordering of these transactions was fully preserved. We stress that the Sequencer never has the ability to steal funds or forge transactions, because every transaction it handles is digitally signed by a user and the signatures are checked by the Arbitrum chain, and at no point were user funds at risk. Furthermore, the Arbitrum bridge continued to operate during this period, and no deposits or withdrawals were lost or at risk at any point.

The root cause of the downtime was a bug causing the Sequencer to get stuck when it received a very large burst of transactions in a short period of time. The issue has been identified and a fix has been deployed.

We also want to clarify the difference between a Sequencer outage (which occurred) and a network outage (which did not occur). Because the Sequencer is the only party who can submit transactions without a delay, a Sequencer outage will cause users to experience downtime. But the Arbitrum network is resilient to sustained Sequencer outages, and even a permanent Sequencer failure (if that were possible) would not prevent the chain from continuing to operate, after a delay. Arbitrum users have the ability to bypass the Sequencer and submit their transactions directly to Ethereum for delayed inclusion in the Arbitrum chain, and this ability was fully preserved during today’s event.

We want to thank you all for bearing with us, and appreciate your understanding. It’s still early days for us and we’ll continue working to provide the best Layer 2 experience for all Ethereum users.