Instances were being incorrectly marked DEAD because their Redis key TTL was
not being refreshed on heartbeat. HealthMonitor.checkRedisHeartbeat() checks
pttl > 0, which fails when the TTL expires even if the instance is alive and
sending regular heartbeats.
Now pexpire(key, heartbeatTtl) is called on each heartbeat to keep the key
alive. Prevents scaling messages from undercounting healthy instances.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Janis
2d76c001fe