There's this setup:

• Kubernetes cluster on Ubuntu with nginx ingress controller
• Flannel network fabric
• Apache 2.4.25 as upstream POD for nginx

The user loads an HTML page and the browser sends several (about 50) asynchronous requests to the server. About 5 out of these 50 requests fail with HTTP 502.

nginx reports:

connect() failed (111: Connection refused) while connecting to upstream

I assume one of the following is happening:

1. Problem with Flannel (too many connections?)
2. Some other issue with my Kubernetes setup

I'd exclude a throttling limitation in Apache since the same setup in Docker (no Kubernetes) runs just fine.

Any ideas?