# Observability
All Observability notes →7 — Multi-Tenancy
Two separate guarantees hiding under one name — data isolation and performance fairness — and the tenant identification, quota enforcement, and selective backpressure that make both hold under shared infrastructure.
8 — Self-Observability
The bootstrapping problem — a platform can't fully trust itself to tell you it's failing — and the two mechanisms that get around it: an independent out-of-band health path, and a synthetic canary that catches silent stalls no internal metric surfaces.
5 — Security & Compliance
Why PII ends up in telemetry by accident rather than by design, the pipeline-layer scrubbing that catches what application discipline misses, tenant-scoped access control, and why the query audit log is itself security-relevant telemetry.
# System Design
All System Design notes →3.6 Multi-Tenancy
Multi-tenancy isolation layers and quota enforcement points across the telemetry ingestion pipeline, from network inbound to the storage write path.
Tenant Identification and Routing at the Ingestion Frontier
How the gateway decides whose data this is — cert/API-key-derived tenant identity, propagation as a Kafka header and X-Scope-OrgID, and the shared-topic-with-filter vs per-tenant-topic vs shuffle-sharded-pool routing trade-off.