Server on kubernetes not responding to UDP calls.

We have encountered an issue with running a relay server that processes UDP calls on DigitalOcean Kubernetes cluster. Even with fully open inbound UDP port range allowing all UDP traffic to go trough firewall, the server still doesn’t seem to respond when pinged.

The k8’s deployment is configured to use host network.

I listed the added firewall rules below.

  [...]
  inbound_rule {
    protocol         = "udp"
    port_range       = "1-65535"
    source_addresses = ["0.0.0.0/0", "::/0"]
  }

  outbound_rule {
    protocol              = "udp"
    port_range            = "1-65535"
    destination_addresses = ["0.0.0.0/0", "::/0"]
  }

  outbound_rule {
    protocol              = "tcp"
    port_range            = "1-65535"
    destination_addresses = ["0.0.0.0/0", "::/0"]
  }

  outbound_rule {
    protocol              = "icmp"
    port_range            = "1-65535"
    destination_addresses = ["0.0.0.0/0", "::/0"]
  }
  [...]

A note: The server works without issues when deployed as a simple docker container without Kubernetes, that leads us to think that the issue could be related Kubernetes, but we haven’t found a specific explanation for that yet.