Why Your Load Balancer Still Sends Traffic to Dead Backends
16 points
3 hours ago
| 2 comments
| singh-sanjay.com
| HN
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AuthAuth
1 hour ago
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It seems like passive is the best option here but can someone explain why one real request must fail? So the load balancer is monitoring for failed requests. If it receives one can it not forward the initial request again?
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cormacrelf
47 minutes ago
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For GET /, sure, and some mature load balancers can do this. For POST /upload_video, no. You'd have to store all in-flight requests, either in-memory or on disk, in case you need to replay the entire thing with a different backend. Not a very good tradeoff.
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jayd16
49 minutes ago
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Not every request is idempotent and its not known when or why a request has failed. GETs are ok (in theory) but you can't retry a POST without risk of side effects.
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singhsanjay12
3 hours ago
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I wrote this after seeing cases where instances were technically “up” but clearly not serving traffic correctly.

The article explores how client-side and server-side load balancing differ in failure detection speed, consistency, and operational complexity.

I’d love input from people who’ve operated service meshes, Envoy/HAProxy setups, or large distributed fleets — particularly around edge cases and scaling tradeoffs.

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