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a83ddbb30e
* Add nodeAffinity to CoreDNS deployment PodSpec to
prefer running CoreDNS pods on controllers, while
relying on podAntiAffinity for spreading.
* For single master clusters, running two CoreDNS pods
on the master or running one pod on a worker is
permissible.
* Note: Its still _possible_ to end up with CoreDNS pods
all running on workers since we only express scheduling
preference ("soft"), but unlikely. Plus the motivating
scenario (below) is also rare.
Background:
* CoreDNS replicas are set to the higher of 2 or the
number of control plane nodes to (at a minimum) support
Deployment updates or pod restarts and match the cluster
size (e.g. 5 master/controller nodes likely means a
larger cluster, so run 5 CoreDNS replicas)
* In the past (before v1.14), we required kube-dns (CoreOS
predecessor) to run CoreDNS pods on master nodes. With
CoreDNS this node selection was relaxed. We'd like a
gentler form of it now.
Motivation:
* On clusters using 100% preemptible/spot workers, it is
possible that CoreDNS pods schedule to workers that are all
preempted at the same time, causing a loss of cluster internal
DNS service until a CoreDNS pod reschedules (1 min). We'd like
CoreDNS to prefer controller/master nodes (which aren't preempted)
to reduce the possibility of control plane disruption
terraform-render-bootstrap
terraform-render-bootstrap is a Terraform module that renders TLS certificates, static pods, and manifests for bootstrapping a Kubernetes cluster.
Audience
terraform-render-bootstrap is a low-level component of the Typhoon Kubernetes distribution. Use Typhoon modules to create and manage Kubernetes clusters across supported platforms. Use the bootstrap module if you'd like to customize a Kubernetes control plane or build your own distribution.
Usage
Use the module to declare bootstrap assets. Check variables.tf for options and terraform.tfvars.example for examples.
module "bootstrap" {
source = "git::https://github.com/poseidon/terraform-render-bootstrap.git?ref=SHA"
cluster_name = "example"
api_servers = ["node1.example.com"]
etcd_servers = ["node1.example.com"]
}
Generate the assets.
terraform init
terraform plan
terraform apply
Find bootstrap assets rendered to the asset_dir path. That's it.