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c12s-kubespray/docs/large-deployments.md
Sergii Golovatiuk c07d60bc90 Kubernetes Reliability Improvements 
- Exclude kubelet CPU/RAM (kube-reserved) from cgroup. It decreases a
  chance of overcommitment
- Add a possibility to modify Kubelet node-status-update-frequency
- Add a posibility to configure node-monitor-grace-period,
  node-monitor-period, pod-eviction-timeout for Kubernetes controller
  manager
- Add Kubernetes Relaibility Documentation with recomendations for
  various scenarios.

Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>
2017-02-09 23:54:08 +01:00

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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 and/or download_localhost: true. See download modes for details.

  • 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.

  • Tune CPU/memory limits and requests. Those are located in roles' defaults and named like foo_memory_limit, foo_memory_requests and foo_cpu_limit, foo_cpu_requests. Note that 'Mi' memory units for K8s will be submitted as 'M', if applied for docker run, and cpu K8s units will end up with the 'm' skipped for docker as well. This is required as docker does not understand k8s units well.

  • Tune kubelet_status_update_frequency to increase reliability of kubelet. kube_controller_node_monitor_grace_period, kube_controller_node_monitor_period, kube_controller_pod_eviction_timeout for better Kubernetes reliability. Check out Kubernetes Reliability

  • Add calico-rr nodes if you are deploying with Calico or Canal. Nodes recover from host/network interruption much quicker with calico-rr. Note that calico-rr role must be on a host without kube-master or kube-node role (but etcd role is okay).

  • Check out the Inventory section of the Getting started guide for tips on creating a large scale Ansible inventory.

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