7.1. Glossary of Terms

Alphabetized definitions with pointers to the section where each concept is developed. Use this for final-week recall drills: cover the definition, recite it, check.

• ACR Task — Registry-integrated build automation supporting quick tasks, commit triggers, base image update triggers, and multi-step YAML pipelines (3.1.2).
• Advanced filter (Event Grid) — Subscription filter evaluating event data payload fields, beyond subject/type matching (4.1.2).
• ANN (Approximate Nearest Neighbor) — Index strategy trading a little recall for large speed gains in vector search; implemented by diskANN, HNSW, IVFFlat (1.1.2).
• App Configuration — Centralized store for non-secret key-values, labels, and feature flags; holds Key Vault references for secrets (5.1.2).
• App settings — Platform-supplied configuration injected as environment variables at container/function runtime (3.1.3, 4.2.2).
• At-least-once delivery — Guarantee that items arrive one or more times; requires idempotent handlers. Applies to change feed, Service Bus, Event Grid (2.1.4, 4.1).
• Autoscale throughput (Cosmos DB) — Provisioning mode scaling between 10–100% of a configured RU/s maximum (2.1.2).
• Azure Container Apps (ACA) — Kubernetes-based container platform with the Kubernetes API hidden; provides revisions, KEDA scaling, Dapr (3.2.1).
• Azure Kubernetes Service (AKS) — Managed Kubernetes with full API access; workloads deployed via manifest files (3.2.3).
• Azure Managed Redis — Managed in-memory data store (Redis Enterprise-based) for caching and vector search (2.3).
• Base image update trigger — ACR Task trigger that rebuilds an image when its FROM image changes upstream (3.1.2).
• Binding (Functions) — Declarative input/output connection to a service, replacing SDK plumbing; plural per function (4.2.1).
• Binding expression — Template token (e.g., {msg.docId}) resolving binding parameters from trigger payload values (4.2.1).
• Bounded staleness — Cosmos DB consistency bounding read lag by K versions or T time; 2x read RU (2.1.2).
• Cache-aside — Caching pattern: check cache, on miss read the durable store and populate the cache with TTL (2.3.1).
• Change feed — Ordered per-partition stream of Cosmos DB inserts and updates (never deletes) (2.1.4).
• Change feed processor — Consumption pattern: monitored container, lease container, host name, delegate; scales by adding instances (2.1.4).
• Cold start — Latency of initializing a function instance when scaling from zero; eliminated by Premium pre-warmed instances (4.2.2).
• Composite index — Cosmos DB index over multiple properties enabling multi-property ORDER BY (2.1.2).
• Consumption plan — Functions hosting with per-execution billing, scale to zero, cold starts, and execution time limits (4.2.2).
• Cosmos DB for NoSQL — Globally distributed document database billing operations in Request Units (2.1).
• CrashLoopBackOff — Kubernetes state: container starts and exits repeatedly; diagnose with kubectl logs --previous (3.2.4).
• Dead-letter queue (DLQ) — Built-in sub-queue holding expired, over-delivered, or explicitly rejected messages until an application reads them (4.1.1).
• DefaultAzureCredential — Credential chain resolving to managed identity in Azure; the identity-over-secrets default (2.1.1, 5.1.1).
• diskANN — Cosmos DB graph-based ANN vector index for large collections (2.1.3).
• Duplicate detection (Service Bus) — Drops messages repeating a message ID within a time window (4.1.1).
• Event — Lightweight fact about something that happened; receivers decide interest; carried by Event Grid (4.1).
• Event Grid — Push-based event routing fabric with filtered subscriptions, 24h retry, and opt-in storage dead-lettering (4.1.2).
• Eventual consistency — Weakest Cosmos DB level: replicas converge with no ordering guarantee (2.1.2).
• Feature flag — Structured on/off switch with rollout filters, stored in App Configuration (5.1.2).
• Flex Consumption plan — Functions hosting adding always-ready instances, faster scale, and VNet support while keeping scale-to-zero (4.2.2).
• Geo-replication (ACR) — Premium SKU feature replicating a registry across regions for local pulls (3.1.1).
• HNSW — Graph-based ANN index (pgvector, Redis): high recall and query speed, slower memory-heavy builds; tune ef_search (2.2.3).
• Idempotency — Property that processing an item twice yields the same outcome; mandatory under at-least-once delivery (2.1.4, 4.1).
• ImagePullBackOff — Kubernetes state: image fetch failing — bad tag or registry auth (3.2.4).
• Indexing policy — Cosmos DB per-container specification of included/excluded index paths (2.1.2).
• IVFFlat — Cluster-based ANN index (pgvector): fast light builds, needs data present before building; tune probes (2.2.3).
• KEDA — Kubernetes Event-driven Autoscaling: scales workloads on event-source metrics (queue length), including to zero (3.2.2).
• Key Vault — Managed store for secrets, keys, and certificates with RBAC, versioning, audit, and soft delete (5.1.1).
• Key Vault reference — Pointer in app settings or App Configuration resolving to a vault secret at runtime via managed identity (3.1.3, 5.1.2).
• KQL (Kusto Query Language) — Read-only, pipe-based language for Log Analytics: table first, then where, summarize, render (5.2.2).
• Lease container — Cosmos DB container storing change feed processor checkpoints and partition ownership (2.1.4).
• Managed identity — Azure-managed service identity with no storable credential; grants resource access via RBAC (5.1.1).
• Message — Command payload whose sender expects processing; carried by Service Bus (4.1).
• Multiple revision mode — ACA mode keeping several revisions live with percentage traffic splitting (canary/blue-green) (3.2.1).
• OpenTelemetry (OTel) — Vendor-neutral standard for traces, metrics, logs; Azure Monitor distro exports to Application Insights (5.2.1).
• Peek-lock — Service Bus receive mode locking a message during processing; consumer must complete, abandon, or dead-letter (4.1.1).
• pgvector — PostgreSQL extension adding the vector(n) type, distance operators, and HNSW/IVFFlat indexes (2.2).
• PgBouncer — Connection pooler built into PostgreSQL Flexible Server (port 6432), multiplexing clients onto few server connections (2.2.5).
• Point read — Cosmos DB fetch by id + partition key: ~1 RU/KB, cheapest read (2.1.1).
• Premium plan (Functions) — Hosting with pre-warmed instances (no cold start), VNet, unbounded duration (4.2.2).
• RAG (Retrieval-Augmented Generation) — Pattern: embed query, retrieve nearest stored chunks, prompt the model with them (1.1.2, 2.2.4).
• Request Unit (RU) — Cosmos DB's normalized currency of operation cost (2.1.2).
• Revision (ACA) — Immutable snapshot of a Container App's template; created by revision-scope changes (3.2.1).
• Semantic cache — Redis pattern serving cached responses for prompts whose embeddings are similar within a threshold (2.3.2).
• Sentinel key — Designated App Configuration key watched by clients; bumping it signals a full config reload (5.1.2).
• Service Bus — Pull-based enterprise message broker: queues, topics/subscriptions, peek-lock, sessions, DLQ (4.1.1).
• Session consistency — Cosmos DB default: read-your-own-writes per session token at 1x RU (2.1.2).
• Sessions (Service Bus) — Ordered, single-consumer processing for messages sharing a session ID (4.1.1).
• Soft delete — Recoverable deletion (Key Vault objects); also the flag-plus-TTL pattern making deletes visible to the change feed (2.1.4, 5.1.1).
• Strong consistency — Cosmos DB level guaranteeing globally latest reads at 2x RU and quorum latency (2.1.2).
• Topic (Service Bus) — Entity where each subscription receives its own copy of every message (pub/sub) (4.1.1).
• Traceparent — W3C header carrying trace context across HTTP hops; stashed in message properties across queues (5.2.1).
• Trigger (Functions) — The single event source that starts a function's execution — exactly one per function (4.2.1).
• VectorDistance — Cosmos DB SQL function computing vector similarity in queries, used in ORDER BY (2.1.3).
• Vector embedding policy — Cosmos DB container policy declaring vector path, dimensions, dataType, and distance function; fixed at creation (2.1.3).
• WEBSITES_PORT — App Service setting declaring a custom container's listening port (3.1.3).
• Zip deploy — Functions deployment of a build artifact, run-from-package for atomic deploys (4.2.2).