System design interview question
"Design webhook delivery. When something happens in our platform, we POST a payload to a URL the customer configured. Customers' endpoints are slow, flaky, and sometimes just gone. Millions of events a day across tens of thousands of customers. It must be reliable and it must not let one bad customer degrade everyone else."
outbound HTTP to untrusted, unreliable third parties — the mirror image of an inbound API. The distinguishing content is: per-customer isolation so one dead endpoint cannot consume the fleet, retry semantics that do not amplify an outage, signing so the receiver can verify authenticity, and the security problem that you are making requests to URLs an untrusted party chose.
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