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1# Kubernetes {#sec-kubernetes}
2
3The NixOS Kubernetes module is a collective term for a handful of
4individual submodules implementing the Kubernetes cluster components.
5
6There are generally two ways of enabling Kubernetes on NixOS. One way is
7to enable and configure cluster components appropriately by hand:
8
9```nix
10{
11 services.kubernetes = {
12 apiserver.enable = true;
13 controllerManager.enable = true;
14 scheduler.enable = true;
15 addonManager.enable = true;
16 proxy.enable = true;
17 flannel.enable = true;
18 };
19}
20```
21
22Another way is to assign cluster roles ("master" and/or "node") to
23the host. This enables apiserver, controllerManager, scheduler,
24addonManager, kube-proxy and etcd:
25
26```nix
27{
28 services.kubernetes.roles = [ "master" ];
29}
30```
31
32While this will enable the kubelet and kube-proxy only:
33
34```nix
35{
36 services.kubernetes.roles = [ "node" ];
37}
38```
39
40Assigning both the master and node roles is usable if you want a single
41node Kubernetes cluster for dev or testing purposes:
42
43```nix
44{
45 services.kubernetes.roles = [ "master" "node" ];
46}
47```
48
49Note: Assigning either role will also default both
50[](#opt-services.kubernetes.flannel.enable)
51and [](#opt-services.kubernetes.easyCerts)
52to true. This sets up flannel as CNI and activates automatic PKI bootstrapping.
53
54::: {.note}
55It is mandatory to configure:
56[](#opt-services.kubernetes.masterAddress).
57The masterAddress must be resolveable and routeable by all cluster nodes.
58In single node clusters, this can be set to `localhost`.
59:::
60
61Role-based access control (RBAC) authorization mode is enabled by
62default. This means that anonymous requests to the apiserver secure port
63will expectedly cause a permission denied error. All cluster components
64must therefore be configured with x509 certificates for two-way tls
65communication. The x509 certificate subject section determines the roles
66and permissions granted by the apiserver to perform clusterwide or
67namespaced operations. See also: [ Using RBAC
68Authorization](https://kubernetes.io/docs/reference/access-authn-authz/rbac/).
69
70The NixOS kubernetes module provides an option for automatic certificate
71bootstrapping and configuration,
72[](#opt-services.kubernetes.easyCerts).
73The PKI bootstrapping process involves setting up a certificate authority (CA)
74daemon (cfssl) on the kubernetes master node. cfssl generates a CA-cert
75for the cluster, and uses the CA-cert for signing subordinate certs issued
76to each of the cluster components. Subsequently, the certmgr daemon monitors
77active certificates and renews them when needed. For single node Kubernetes
78clusters, setting [](#opt-services.kubernetes.easyCerts)
79= true is sufficient and no further action is required. For joining extra node
80machines to an existing cluster on the other hand, establishing initial
81trust is mandatory.
82
83To add new nodes to the cluster: On any (non-master) cluster node where
84[](#opt-services.kubernetes.easyCerts)
85is enabled, the helper script `nixos-kubernetes-node-join` is available on PATH.
86Given a token on stdin, it will copy the token to the kubernetes secrets directory
87and restart the certmgr service. As requested certificates are issued, the
88script will restart kubernetes cluster components as needed for them to
89pick up new keypairs.
90
91::: {.note}
92Multi-master (HA) clusters are not supported by the easyCerts module.
93:::
94
95In order to interact with an RBAC-enabled cluster as an administrator,
96one needs to have cluster-admin privileges. By default, when easyCerts
97is enabled, a cluster-admin kubeconfig file is generated and linked into
98`/etc/kubernetes/cluster-admin.kubeconfig` as determined by
99[](#opt-services.kubernetes.pki.etcClusterAdminKubeconfig).
100`export KUBECONFIG=/etc/kubernetes/cluster-admin.kubeconfig` will make
101kubectl use this kubeconfig to access and authenticate the cluster. The
102cluster-admin kubeconfig references an auto-generated keypair owned by
103root. Thus, only root on the kubernetes master may obtain cluster-admin
104rights by means of this file.