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c12s-kubespray/docs/large-deployments.md
Matthew Mosesohn 5f12b7aedf Remove kubedns and dnsmasq. Move dns_late phase after apps (#4406) 
Both kubedns and dnsmasq modes are long not maintained.
We should run dns_late steps at the end because sshd
makes DNS lookups during Ansible run and has 2s timeouts
for each failed lookup trying to connect to coredns before
it is ready.
2019-04-01 12:32:34 -07:00

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Large deployments of K8s

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

  • Tune ansible settings 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 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

  • Tune network prefix sizes. Those are kube_network_node_prefix, kube_service_addresses and kube_pods_subnet.

  • 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.

  • Override the etcd_events_cluster_setup: true store events in a separate dedicated etcd instance.

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