Layer 3 · Go deeper · 7 min
Go deeper
Size it, build it, then make the calls an interviewer will push you on.
Back of the envelope
Size it up
Tap through each step of the arithmetic.
Every router pulls the full tenant map every 5 seconds. How much traffic?
How much does a 1% canary cut a bad config’s exposure?
Build-up · 6 steps
Follow one config change to every cell
A new tenant’s routing entry must reach every cell before its first request. Every control plane, from istiod to a SaaS tenant catalog, runs this loop.
Step 1 of 6
Write and validate
The new tenant’s entry arrives by console, API or pull request. Invariants, like every tenant mapping to a real stamp, are checked before it’s stored, so a broken map is never published.
4 interview moments
You’re the candidate
The interviewer pushes on the hard parts. Pick an approach and see how it holds up.
Deep dive 1 of 4
Interviewer
“Your router needs each tenant’s stamp on every request, 50,000 times a second. Where does it get it?”
The control plane owns the tenant-to-stamp map. It targets, say, 99.9% and is sized for about 5 writes a second.
Your move. Pick an approach:
Deep dive 2 of 4
Interviewer
“A minor change to a regex rule is ready. Your config system can reach every node in seconds. How do you ship it?”
Your move. Pick an approach:
Deep dive 3 of 4
Interviewer
“The control plane is down for hours. Nodes can’t refresh the tenant map, flags or revoked API keys. What do they do?”
Your move. Pick an approach:
Deep dive 4 of 4
Interviewer
“You run a service across three zones. If one fails, how do you make sure the other two can carry the load?”
Your move. Pick an approach: