Summary of the Amazon DynamoDB Service Disruption in US-East-1 Region

So the DNS records if-stale-then-needs-update it was basically a variation of the "2 Hard Things In Computer Science - cache invalidation". Excerpt from the giant paragraph:

>[...] Right before this event started, one DNS Enactor experienced unusually high delays needing to retry its update on several of the DNS endpoints. As it was slowly working through the endpoints, several other things were also happening. First, the DNS Planner continued to run and produced many newer generations of plans. Second, one of the other DNS Enactors then began applying one of the newer plans and rapidly progressed through all of the endpoints. The timing of these events triggered the latent race condition. When the second Enactor (applying the newest plan) completed its endpoint updates, it then invoked the plan clean-up process, which identifies plans that are significantly older than the one it just applied and deletes them. At the same time that this clean-up process was invoked, the first Enactor (which had been unusually delayed) applied its much older plan to the regional DDB endpoint, overwriting the newer plan. The check that was made at the start of the plan application process, which ensures that the plan is newer than the previously applied plan, was stale by this time due to the unusually high delays in Enactor processing. [...]

It outlines some of the mechanics but some might think it still isn't a "Root Cause Analysis" because there's no satisfying explanation of _why_ there were "unusually high delays in Enactor processing". Hardware problem?!? Human error misconfiguration causing unintended delays in Enactor behavior?!? Either the previous sequence of events leading up to that is considered unimportant, or Amazon is still investigating what made Enactor behave in an unpredictable way.

This is public messaging to explain the problem at large. This isnt really a post incident analysis.

Before the active incident is “resolved” theres an evaluation of probable/plausible reoccurrence. Usually we/they would have potential mitigations and recovery runbooks prepared as well to quickly react to any reoccurance. Any likely open risks are actively worked to mitigate before the immediate issue is considered resolved. That includes around-the-clock dev team work if its the best known path to mitigation.

Next any plausible paths to “risk of reoccurance” would be top dev team priority (business hours) until those action items are completed and in deployment. That might include other teams with similar DIY DNS management, other teams who had less impactful queue depth problems, or other similar “near miss” findings. Service team tech & business owners (PE, Sr PE, GM, VP) would be tracking progress daily until resolved.

Then in the next few weeks at org & AWS level “ops meetings” there are going to be the in depth discussions of the incident, response, underlying problems, etc. the goal there being organizational learning and broader dissemination of lessons learned, action items, best practice etc.