My load balancer's HTTPS only works sometimes

It's possible you have:

• A load balancer with cross-zone load balancing switched off (for NLB & GLB it's off by default)
• Not all of your load balancer's AZs with a valid working target.

So some requests would succeed and some fail.

Hello Yuri,

An additional component to check is the healthcheck around your target groups/instances. It could be possible that no healthy instances for your HTTPS target group could be found.

You should be able to check the health status under "target groups" in the AWS console.

Below is some additional documentation from AWS around these health checks.

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-health-checks.html

I am experiencing the same with my load balancer. It sometimes gives a 504, and sometimes not.

This seems to happen only with instances outside the load balancer's VPC, that are specified by their internal IP. The health check is working fine, the instances are healthy all the time.