API Gateway

A resilience pattern that prevents an application from repeatedly calling a failing service. When failures exceed a threshold, the circuit 'opens' and fails fast, allowing the backend service time to recover before allowing traffic again. This is critical for preventing cascading failures in distributed systems where an API Gateway routes requests.

• Key Mechanism: Monitors for failures (e.g., timeouts, HTTP 5xx errors).
• States: Closed (normal operation), Open (failing fast), Half-Open (testing recovery).
• Use Case: Protects backend microservices from being overwhelmed by retry storms originating from client calls, including those mediated by an AI agent.

A unique client-generated identifier (often a UUID) sent with a state-changing request (like POST or PUT) to ensure the operation is performed exactly once. The API Gateway or backend service uses this key to deduplicate requests, returning the same result for subsequent calls with the same key. This is essential for reliable orchestration where network timeouts or agent retries could cause duplicate calls.

• How it works: The server stores the key and the response of the first successful request.
• Prevents: Double charges, duplicate orders, or inconsistent state.
• Agent Integration: AI agents making tool calls should generate and attach idempotency keys to all non-idempotent API requests to guarantee safe retries.

An API Gateway that enforces a zero-trust security model, where no request is trusted by default, regardless of its origin. It performs continuous authentication, authorization, and inspection of all API traffic. For AI agents, this means every tool call is rigorously validated.

• Core Principles: Least privilege access, explicit verification, and assume breach.
• Enforces: Strict identity verification (mTLS, JWT validation), fine-grained policy checks, and request/response body inspection.
• Critical for Agents: Acts as a policy enforcement point (PEP) for autonomous systems, ensuring they only access authorized endpoints with appropriate parameters.

A diagnostic technique that tracks a request's journey as it propagates through a distributed system, including hops through an API Gateway and various microservices. It provides a unified view of latency, errors, and dependencies, which is vital for debugging orchestrated AI agent workflows.

• Key Concepts: Trace (the entire request journey), Span (a single operation within a trace), and Context Propagation (passing trace IDs across service boundaries).
• Tools: OpenTelemetry, Jaeger, Zipkin.
• Observability Value: Allows engineers to see the full chain of tool calls an agent makes, identify bottlenecks at the gateway or backend, and understand failure propagation.

The programmatic verification of API call inputs (requests) and outputs (responses) against formally defined schemas (e.g., OpenAPI, JSON Schema). An API Gateway often performs initial validation, rejecting malformed requests before they reach business logic. This is a foundational safety mechanism for structured output guarantees from AI agents.

• Prevents: Injection attacks, malformed data, and contract violations.
• Validation Layers: Syntax (JSON well-formedness), schema (data types, required fields), and semantic (business logic) validation.
• Agent Safety: Ensures the parameters generated by an LLM for a tool call are structurally correct, reducing runtime errors and unpredictable behavior.

A retry algorithm where the waiting time between consecutive retry attempts increases exponentially. It is used to handle transient failures (e.g., network glitches, temporary throttling) in calls to external APIs. An orchestration layer or API client implementing this pattern prevents overwhelming a recovering service.

• Formula: Delay = base_delay * (2 ^ attempt_number). Often combined with jitter (random variation) to avoid thundering herds.
• Use Case: When an API Gateway returns a 429 Too Many Requests or 503 Service Unavailable status code.
• Agent Implementation: AI agent frameworks should embed this logic for autonomous retries of failed tool calls, respecting Retry-After headers when present.