40 customers, 4 cells, one of them hot and one customer locked to the EU. How do you decide where a new tenant goes?

Modulo hashing reshuffles everyone the day you add a cell. Consistent hashing fixes that and then loses to the two constraints that actually decide placement in an enterprise deployment: jurisdiction and who must not share a blast radius with whom.

Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

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UP NEXT ON YOUR JOURNEY

Next in this trackThe customer signs a hardware order on Friday and asks how many GPUs. You have no access to their environment. What number do you give?Next in this trackTheir order system goes down for four hours a week and cannot be changed. Design the queue that sits between it and your pipeline.Next in this trackForty deployments, and the platform median looks fine while three customers are having their worst week. Design the metrics pipeline.

FEDITOR'S NOTE

The senior signal is knowing consistent hashing well enough to say where it stops being the right tool. A candidate who reaches for it and stops has answered a distributed-systems question; a candidate who reaches for it and then notices that a regulated tenant cannot be placed by a hash function has answered a deployment question. The reserve probe is the rebalance: moving a tenant between cells means moving their data, and a design that treats placement as stateless has not thought about what a cell contains. Watch for candidates who propose per-tenant weights without saying where the weight comes from, and for anyone who never asks whether two tenants are competitors.

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