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terraform-module-k3s

Terraform Version GitHub tag (latest SemVer) GitHub issues Open Source Helpers MIT Licensed

Terraform module to create a k3s cluster with multi-server and annotations/labels/taints management features.

⚠️ Security disclosure

Because the use of external references on the destroy provisioner is deprecated by Terraform, storing information inside each resource is mandatory in order to manage several functionalities such as automatic node draining and field management. As a result, several fields such as the connection block will be available in your TF state. This means that the password or private key used will be clearly readable in this TF state.
Please be very careful to store your TF state securely if you use a private key or password in the connection block.

Example (based on Hetzner Cloud example)

module "k3s" {
  source = "xunleii/k3s/module"

  depends_on_    = hcloud_server.agents
  k3s_version    = "latest"
  cluster_domain = "cluster.local"
  cidr = {
    pods     = "10.42.0.0/16"
    services = "10.43.0.0/16"
  }
  drain_timeout  = "30s"
  managed_fields = ["label", "taint"] // ignore annotations

  global_flags = [
    "--flannel-iface ens10",
    "--kubelet-arg cloud-provider=external" // required to use https://github.com/hetznercloud/hcloud-cloud-controller-manager
  ]

  servers = {
    for i in range(length(hcloud_server.control_planes)) :
    hcloud_server.control_planes[i].name => {
      ip = hcloud_server_network.control_planes[i].ip
      connection = {
        host        = hcloud_server.control_planes[i].ipv4_address
        private_key = trimspace(tls_private_key.ed25519_provisioning.private_key_pem)
      }
      flags = [
        "--disable-cloud-controller",
        "--tls-san ${hcloud_server.control_planes[0].ipv4_address}",
      ]
      annotations = { "server_id" : i } // theses annotations will not be managed by this module
    }
  }

  agents = {
    for i in range(length(hcloud_server.agents)) :
    "${hcloud_server.agents[i].name}_node" => {
      name = hcloud_server.agents[i].name
      ip   = hcloud_server_network.agents_network[i].ip
      connection = {
        host        = hcloud_server.agents[i].ipv4_address
        private_key = trimspace(tls_private_key.ed25519_provisioning.private_key_pem)
      }

      labels = { "node.kubernetes.io/pool" = hcloud_server.agents[i].labels.nodepool }
      taints = { "dedicated" : hcloud_server.agents[i].labels.nodepool == "gpu" ? "gpu:NoSchedule" : null }
    }
  }
}

Inputs

Name Description Type Default Required
servers K3s server nodes definition. The key is used as node name if no name is provided. map(any) n/a yes
agents K3s agent nodes definitions. The key is used as node name if no name is provided. map(any) {} no
cidr K3s network CIDRs (see https://rancher.com/docs/k3s/latest/en/installation/install-options/).
object({
pods = string
services = string
})
{
"pods": "10.42.0.0/16",
"services": "10.43.0.0/16"
}
no
cluster_domain K3s cluster domain name (see https://rancher.com/docs/k3s/latest/en/installation/install-options/). string "cluster.local" no
depends_on_ Resource dependency of this module. any null no
drain_timeout The length of time to wait before giving up the node draining. Infinite by default. string "0s" no
generate_ca_certificates If true, this module will generate the CA certificates (see k3s-io/k3s#1868 (comment)). Otherwise rancher will generate it. This is required to generate kubeconfig bool true no
global_flags Add additional installation flags, used by all nodes (see https://rancher.com/docs/k3s/latest/en/installation/install-options/). list(string) [] no
k3s_install_env_vars map of enviroment variables that are passed to the k3s installation script (see https://docs.k3s.io/reference/env-variables) map(string) {} no
k3s_version Specify the k3s version. You can choose from the following release channels or pin the version directly string "latest" no
kubernetes_certificates A list of maps of cerificate-name.[crt/key] : cerficate-value to copied to /var/lib/rancher/k3s/server/tls, if this option is used generate_ca_certificates will be treat as false
list(
object({
file_name = string,
file_content = string
})
)
[] no
managed_fields List of fields which must be managed by this module (can be annotation, label and/or taint). list(string)
[
"annotation",
"label",
"taint"
]
no
name K3s cluster domain name (see https://rancher.com/docs/k3s/latest/en/installation/install-options/). This input is deprecated and will be remove in the next major release. Use cluster_domain instead. string "!!!DEPRECATED!!!" no
separator Separator used to separates node name and field name (used to manage annotations, labels and taints). string "|" no
use_sudo Whether or not to use kubectl with sudo during cluster setup. bool false no

Outputs

Name Description
kube_config Genereated kubeconfig.
kubernetes Authentication credentials of Kubernetes (full administrator).
kubernetes_cluster_secret Secret token used to join nodes to the cluster
kubernetes_ready Dependency endpoint to synchronize k3s installation and provisioning.
summary Current state of k3s (version & nodes).

Providers

Name Version
http ~> 3.0
null ~> 3.0
random ~> 3.0
tls ~> 4.0

Frequently Asked Questions

How to customise the generated kubeconfig

It is sometimes necessary to modify the context or the cluster name to adapt kubeconfig to a third-party tool or to avoid conflicts with existing tools. Although this is not the role of this module, it can easily be done with its outputs :

module "k3s" {
  ...
}

local {
  kubeconfig = yamlencode({
    apiVersion      = "v1"
    kind            = "Config"
    current-context = "my-context-name"
    contexts = [{
      context = {
        cluster = "my-cluster-name"
        user : "my-user-name"
      }
      name = "my-context-name"
    }]
    clusters = [{
      cluster = {
        certificate-authority-data = base64encode(module.k3s.kubernetes.cluster_ca_certificate)
        server                     = module.k3s.kubernetes.api_endpoint
      }
      name = "my-cluster-name"
    }]
    users = [{
      user = {
        client-certificate-data : base64encode(module.k3s.kubernetes.client_certificate)
        client-key-data : base64encode(module.k3s.kubernetes.client_key)
      }
      name : "my-user-name"
    }]
  })
}

License

terraform-module-k3s is released under the MIT License. See the bundled LICENSE file for details.

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