ALB and target Group : Health check failure

Dear Team,

I am working on one ALB application , that DNS i mapped with my Godaddy credentials, my server also up and running , no issues anywhere but still my Target group status showing Unhealthy after few minutes of instance launched and getting drained and launching new instance, like this its repeating. If i check my ASG , i gave desired, minimum and maximum capacity as '1' , but still before terminating the old instance its creating new instance once the other comes 2/2 checks passed, old instance getting drained by themself. so its not affecting my server running status anywhere but still, without any load why this health check failure happening, if i open the target group attributes , there i can find 'DNS Failover + Fail Open' , what is that unable to find any solution for this Please assist