Kernel network tunables need better defaults and to be configurable

[James Troup]

Through bitter experience in OpenStack we've discovered the need to tweak some of Linux's network tunable parameters. I strongly suspect those same parameters need tuned on CDK too.

The OpenStack charms default to the following changes:

      { net.ipv4.neigh.default.gc_thresh1 : 128,
        net.ipv4.neigh.default.gc_thresh2 : 28672,
        net.ipv4.neigh.default.gc_thresh3 : 32768,
        net.ipv6.neigh.default.gc_thresh1 : 128,
        net.ipv6.neigh.default.gc_thresh2 : 28672,
        net.ipv6.neigh.default.gc_thresh3 : 32768,
        net.nf_conntrack_max : 1000000,
        net.netfilter.nf_conntrack_buckets : 204800,
        net.netfilter.nf_conntrack_max : 1000000 }

Others have run into the need to change gc_thresh when running Kubernetes at scale, e.g.:

  https://<email address hidden>/tinders-move-to-kubernetes-cda2a6372f44

And any CDK charm which enables iptables on a host should consider having support for both changing the conntrack settings and have defaults like those above.

[Tim Van Steenburgh (tvansteenburgh)]

Implementation in nova-compute: https://github.com/openstack/charm-nova-compute/blob/master/hooks/nova_compute_hooks.py#L184-L195

[Mike Wilson (knobby)]

https://github.com/charmed-kubernetes/layer-kubernetes-master-worker-base/pull/3
https://github.com/charmed-kubernetes/charm-kubernetes-worker/pull/4

[Tim Van Steenburgh (tvansteenburgh)]

Will be available in kubernetes-worker-523 and later, and kubernetes-master-661 and later.

[George Kraft (cynerva)]

PRs to stable:
https://github.com/charmed-kubernetes/layer-kubernetes-master-worker-base/pull/4
https://github.com/charmed-kubernetes/charm-kubernetes-worker/pull/19

[George Kraft (cynerva)]

Fix is available in candidate channels:
cs:~containers/kubernetes-master-684
cs:~containers/kubernetes-worker-541

[George Kraft (cynerva)]

Fix released to stable with these charm revisions:
cs:~containers/kubernetes-master-684
cs:~containers/kubernetes-worker-541