Why one cloud outage takes down half the Internet
Race condition: why three copies of one program did not prevent the AWS outage
AWS ran three copies of the program behind one of its most important DNS records, to be safe. How did copies kept for safety end up emptying that record?
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Behind the name of DynamoDB stand two programs of AWS. The first, the Planner, keeps an eye on the machines of DynamoDB and writes a fresh plan every so often: the list of addresses the name should give.
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The second, the Enactor, copies the newest plan into the DNS record, over the one before. To be safe, AWS ran three copies of it, one in each of three zones: if one stops, the two others go on.
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