HttpClientFactory and Polly: Making External HTTP Calls More Resilient

External HTTP calls are naturally unstable: network jitter, DNS changes, rate limits, and occasional 5xx responses happen. Reliability cannot be solved by blindly retrying.

Call Flow

sequenceDiagram
    participant H as Handler
    participant C as Typed HttpClient
    participant P as Polly Policy
    participant API as External API
    H->>C: Call third-party service
    C->>P: Apply timeout / retry / circuit breaker
    P->>API: HTTP request
    API-->>P: 2xx / 5xx / timeout
    P-->>C: Success / fallback / fast fail
    C-->>H: Business result

Engineering Scenario

HttpClientFactory manages handler lifetime and connection reuse. Polly manages failure policies. Together they make timeout, retry, and circuit-breaking behavior explicit.

Best Practices

• Set clear timeouts first.
• Retry only transient failures.
• Keep retry counts small and observable.
• Design circuit breaking, fallback, and alerts together.