Reduce Calcio MTU on Fedora CoreOS Azure

* Change the Calico VXLAN interface for MTU from 1450 to 1410
* VXLAN on Azure should support MTU 1450. However, there is
history where performance measures have shown that 1410 is
needed to have expected performance. Flatcar Linux has the
same MTU 1410 override and note
* FCOS 31.20200323.3.2 was known to perform fine with 1450, but
now in 31.20200517.3.0 the right value seems to be 1410

CHANGES.md

@@ -26,6 +26,7 @@ Notable changes between versions.
 #### Azure
 
 * Use `strict` Fedora CoreOS Config (FCC) snippet parsing ([#755](https://github.com/poseidon/typhoon/pull/755))
+* Reduce Calico vxlan interface MTU to maintain performance ([#767](https://github.com/poseidon/typhoon/pull/766))
 
 #### AWS
 

azure/fedora-coreos/kubernetes/bootstrap.tf

@@ -10,8 +10,9 @@ module "bootstrap" {
   networking = var.networking
 
   # only effective with Calico networking
+  # we should be able to use 1450 MTU, but in practice, 1410 was needed
   network_encapsulation = "vxlan"
-  network_mtu           = "1450"
+  network_mtu           = "1410"
 
   pod_cidr              = var.pod_cidr
   service_cidr          = var.service_cidr