System Type: Azure

Patterns, failure modes, and anti-patterns for systems built on Microsoft Azure.

Compute

Azure App Service

When to use. Web applications, REST APIs, and backend services where you want managed infrastructure with zero Kubernetes overhead. Supports .NET, Java, Node.js, Python, Go. Built-in autoscaling, deployment slots, and custom domains with managed TLS. When to avoid. Workloads that need GPU, custom networking at the host level, or containers with sidecar patterns. When per-second billing matters (App Service charges per plan, not per request). Workloads that need sub-second cold start. Key decisions. Plan tier (Free/Basic for dev, Standard/Premium for production — Premium required for VNet integration and deployment slots), Linux vs Windows, scaling rules (CPU, memory, HTTP queue length, custom metrics), always-on setting (prevents cold starts on Standard+), deployment slot swap strategy.

Azure Functions

When to use. Event-driven, short-lived compute — HTTP triggers, queue processors, timer-based jobs, event hub consumers. Consumption plan gives true pay-per-execution. Ideal for glue logic, webhooks, and lightweight APIs. When to avoid. Long-running processes (Consumption plan has a 5/10-minute timeout). Workloads with sustained high throughput (Consumption plan cold starts add latency; Premium or Dedicated plan negates the cost advantage). Complex orchestration (use Durable Functions or Container Apps instead). Key decisions. Hosting plan (Consumption for sporadic traffic, Premium for VNet and pre-warmed instances, Dedicated for predictable load), runtime version, trigger binding selection, Durable Functions for orchestration/fan-out, function app isolation boundaries (one app per domain concern).