Sticky affinity on the ingress is fine for session-in-memory apps, but the failure mode that bites us is pod churn: a rolling update or node drain invalidates the affinity cookie and dumps users onto cold JVMs. With nginx ingress I keep affinity cookie-based (not pure ip_hash) so NAT fleets do not pin an entire office to one replica, set a short cookie max-age aligned with the WildFly session timeout, and make sure the upstream still accepts a new session without a hard error when the sticky target disappears.

For safer ops I treat stickiness as a temporary bridge, not architecture: enable session replication or an external store for anything that cannot rebuild state, and watch 502/504 spikes plus upstream response time during deploys — those usually mean affinity pointed at a terminating pod. Also verify that health checks remove the pod from the endpoints list before SIGTERM finishes; otherwise sticky clients keep hammering a half-dead WildFly until the cookie expires. If you can move auth tokens or carts out of heap, drop affinity later and go back to plain round-robin.