# System Design
All System Design notes →Q1: 500M Samples/Sec, Zero Drop on Rolling Deploy
Full principal-level solution: design a telemetry ingestion pipeline for 500M metric samples/sec from 100K services globally with a zero-drop guarantee during rolling deployment of the ingestion tier.
Q10: Self-Service Tenant Onboarding With Zero Platform-Team Involvement
Full principal-level solution: design a self-service tenant onboarding API for a telemetry pipeline that protects shared infrastructure from a misbehaving new tenant on day one.
Q11: Redesigning the Ingestion Frontier for a Compromised-Agent Threat Model
Full principal-level solution: redesign the telemetry ingestion frontier assuming a compromised agent sends malformed and adversarial payloads — oversized batches, spoofed tenant IDs, garbage label values.
Q12: Exactly-Once for One Billing Tenant While Others Stay At-Least-Once
Full principal-level solution: support exactly-once ingestion for a single billing-critical tenant in a shared pipeline that is at-least-once everywhere else, and account for what it costs.
Q2: Cardinality Storm — Detect and Mitigate Without Affecting Other Tenants
Full principal-level solution: a tenant sends 50M unique label combinations/minute causing TSDB compaction storms — design detection and mitigation that isolates the blast radius to that tenant.
Q3: Trace Sampling Loses Spans During Incident Peaks — Redesign
Full principal-level solution: the trace pipeline drops spans exactly when incidents spike trace volume — diagnose the failure mode and redesign the tail-sampling pipeline to survive it.
Q4: A Metric's Journey From Pod to Dashboard — Every Failure Point
Full principal-level solution: trace a single metric data point from a Kubernetes pod to a queryable dashboard, identifying every failure point along the way and how each is detected.
Q5: Adding Continuous Profiling to an Existing MELT Pipeline
Full principal-level solution: extend an existing metrics + logs + traces pipeline with continuous profiling as a fourth signal, without a full redesign.
Q6: Compactor Queue Backing Up During a Multi-Tenant Flush
Full principal-level solution: diagnose a compactor backlog causing query latency spikes during a large multi-tenant flush, and mitigate it without pausing ingestion.
Q7: A Region's Gateway Goes Dark — Blast Radius Walkthrough and Redesign
Full principal-level solution: walk through the consequences of a 10-minute regional ingestion gateway outage, then redesign the topology to shrink the blast radius.
Q8: Counters Resetting to Zero After an OTel SDK Upgrade
Full principal-level solution: diagnose and fix a tenant's dashboards showing counters reset to zero every few minutes after an OTel SDK upgrade, without requiring instrumentation changes.
Q9: Cut Ingestion Infrastructure Cost 40% Without Violating SLOs
Full principal-level solution: a FinOps-driven cost-reduction pass on a telemetry ingestion pipeline — where to look first, what levers exist at each layer, and what you trade away.