DNS Caching Duration in SocketsHttpHandler: 5‑Minute Limit

Problem Statement

The HttpClient in .NET uses SocketsHttpHandler to resolve hostnames. Internally the handler caches DNS lookups for a default period of five minutes per host. This interval is hard‑coded in the runtime and is not exposed through any public API or configuration setting. Consequently, if a host’s IP address changes within that window, subsequent requests may continue to use a stale IP, leading to failed connections or delayed failover.

Constraints & Uncertainty

• The 5‑minute cache is per HttpClient instance; creating a new instance clears the cache.
• No documented configuration exists to adjust the cache duration or to set a per‑host TTL.
• Workarounds such as setting PooledConnectionLifetime to TimeSpan.Zero or creating a new client per request increase DNS overhead.

Open Questions

• Does the .NET team plan to expose a public API to configure the DNS cache duration in future releases?
• Is there a supported mechanism to override the cache on a per‑host basis without impacting overall throughput?
• How does this hard‑coded behavior affect applications that rely on rapid failover to new IP addresses?