c12s-kubespray/docs/large-deployments.md

Large deployments of K8s
========================

For a large scaled deployments, consider the following configuration changes:

* Tune [ansible settings](http://docs.ansible.com/ansible/intro_configuration.html)
  for `forks` and `timeout` vars to fit large numbers of nodes being deployed.

* Override containers' `foo_image_repo` vars to point to intranet registry.

* Override the ``download_run_once: true`` to download container images only once
  then push to cluster nodes in batches. The default delegate node
  for pushing images is the first kube-master. Note, if you have passwordless sudo
  and docker enabled on the separate admin node, you may want to define the
  ``download_localhost: true``, which makes that node a delegate for pushing images
  while running the deployment with ansible. This maybe the case if cluster nodes
  cannot access each over via ssh or you want to use local docker images as a cache
  for multiple clusters.

* Adjust the `retry_stagger` global var as appropriate. It should provide sane
  load on a delegate (the first K8s master node) then retrying failed
  push or download operations.

* Tune parameters for DNS related applications (dnsmasq daemon set, kubedns
  replication controller). Those are ``dns_replicas``, ``dns_cpu_limit``,
  ``dns_cpu_requests``, ``dns_memory_limit``, ``dns_memory_requests``.
  Please note that limits must always be greater than or equal to requests.

For example, when deploying 200 nodes, you may want to run ansible with
``--forks=50``, ``--timeout=600`` and define the ``retry_stagger: 60``.