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Shared projects issues of December 7 & 8, 2021

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On December 7th, you might have noticed issues in your shared Todoist projects. We know that many rely on shared projects to stay on top of work and life. We apologize for this disruption and we'd like to share what we're doing to make sure it doesn't happen again in the future.

Our cloud provider, Amazon Web Services, experienced an outage on December 7, partially affecting our services. However, because of the outage, we couldn't pinpoint the issues in the Todoist system for hours — or roll out fixes to address them. Once we were able to provide fixes, our systems had millions of tasks to process, which took hours to fully recover.

This happened because of the way shared projects work. Right now, every person sharing a Todoist project has a replica of the project. When there is a change, it needs to be pushed out to all other replicas. This is a fragile model, with many moving parts and points of failure. We used this method as a compromise when we first built shared projects back in 2015 — but now that they're one of Todoist's most popular features, this compromise is no longer efficient.

The good news is that we're halfway through a significant upgrade for shared projects — where everyone in the project shares a single source of truth. It will mitigate issues like the one you just experienced. It's taken time, but this change will roll out to all Todoist shared projects in the first half of 2022.

Thank you for being a Todoister!