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126 lines
5.4 KiB
XML
126 lines
5.4 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-kubernetes">
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<title>Kubernetes</title>
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<para>
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The NixOS Kubernetes module is a collective term for a handful of
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individual submodules implementing the Kubernetes cluster
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components.
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</para>
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<para>
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There are generally two ways of enabling Kubernetes on NixOS. One
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way is to enable and configure cluster components appropriately by
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hand:
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</para>
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<programlisting language="bash">
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services.kubernetes = {
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apiserver.enable = true;
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controllerManager.enable = true;
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scheduler.enable = true;
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addonManager.enable = true;
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proxy.enable = true;
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flannel.enable = true;
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};
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</programlisting>
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<para>
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Another way is to assign cluster roles ("master" and/or
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"node") to the host. This enables apiserver,
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controllerManager, scheduler, addonManager, kube-proxy and etcd:
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</para>
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<programlisting language="bash">
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services.kubernetes.roles = [ "master" ];
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</programlisting>
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<para>
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While this will enable the kubelet and kube-proxy only:
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</para>
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<programlisting language="bash">
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services.kubernetes.roles = [ "node" ];
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</programlisting>
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<para>
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Assigning both the master and node roles is usable if you want a
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single node Kubernetes cluster for dev or testing purposes:
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</para>
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<programlisting language="bash">
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services.kubernetes.roles = [ "master" "node" ];
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</programlisting>
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<para>
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Note: Assigning either role will also default both
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<xref linkend="opt-services.kubernetes.flannel.enable" /> and
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<xref linkend="opt-services.kubernetes.easyCerts" /> to true. This
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sets up flannel as CNI and activates automatic PKI bootstrapping.
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</para>
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<para>
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As of kubernetes 1.10.X it has been deprecated to open
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non-tls-enabled ports on kubernetes components. Thus, from NixOS
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19.03 all plain HTTP ports have been disabled by default. While
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opening insecure ports is still possible, it is recommended not to
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bind these to other interfaces than loopback. To re-enable the
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insecure port on the apiserver, see options:
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<xref linkend="opt-services.kubernetes.apiserver.insecurePort" />
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and
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<xref linkend="opt-services.kubernetes.apiserver.insecureBindAddress" />
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</para>
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<note>
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<para>
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As of NixOS 19.03, it is mandatory to configure:
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<xref linkend="opt-services.kubernetes.masterAddress" />. The
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masterAddress must be resolveable and routeable by all cluster
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nodes. In single node clusters, this can be set to
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<literal>localhost</literal>.
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</para>
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</note>
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<para>
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Role-based access control (RBAC) authorization mode is enabled by
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default. This means that anonymous requests to the apiserver secure
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port will expectedly cause a permission denied error. All cluster
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components must therefore be configured with x509 certificates for
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two-way tls communication. The x509 certificate subject section
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determines the roles and permissions granted by the apiserver to
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perform clusterwide or namespaced operations. See also:
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<link xlink:href="https://kubernetes.io/docs/reference/access-authn-authz/rbac/">
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Using RBAC Authorization</link>.
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</para>
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<para>
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The NixOS kubernetes module provides an option for automatic
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certificate bootstrapping and configuration,
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<xref linkend="opt-services.kubernetes.easyCerts" />. The PKI
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bootstrapping process involves setting up a certificate authority
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(CA) daemon (cfssl) on the kubernetes master node. cfssl generates a
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CA-cert for the cluster, and uses the CA-cert for signing
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subordinate certs issued to each of the cluster components.
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Subsequently, the certmgr daemon monitors active certificates and
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renews them when needed. For single node Kubernetes clusters,
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setting <xref linkend="opt-services.kubernetes.easyCerts" /> = true
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is sufficient and no further action is required. For joining extra
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node machines to an existing cluster on the other hand, establishing
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initial trust is mandatory.
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</para>
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<para>
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To add new nodes to the cluster: On any (non-master) cluster node
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where <xref linkend="opt-services.kubernetes.easyCerts" /> is
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enabled, the helper script
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<literal>nixos-kubernetes-node-join</literal> is available on PATH.
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Given a token on stdin, it will copy the token to the kubernetes
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secrets directory and restart the certmgr service. As requested
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certificates are issued, the script will restart kubernetes cluster
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components as needed for them to pick up new keypairs.
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</para>
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<note>
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<para>
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Multi-master (HA) clusters are not supported by the easyCerts
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module.
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</para>
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</note>
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<para>
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In order to interact with an RBAC-enabled cluster as an
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administrator, one needs to have cluster-admin privileges. By
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default, when easyCerts is enabled, a cluster-admin kubeconfig file
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is generated and linked into
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<literal>/etc/kubernetes/cluster-admin.kubeconfig</literal> as
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determined by
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<xref linkend="opt-services.kubernetes.pki.etcClusterAdminKubeconfig" />.
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<literal>export KUBECONFIG=/etc/kubernetes/cluster-admin.kubeconfig</literal>
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will make kubectl use this kubeconfig to access and authenticate the
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cluster. The cluster-admin kubeconfig references an auto-generated
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keypair owned by root. Thus, only root on the kubernetes master may
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obtain cluster-admin rights by means of this file.
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</para>
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</chapter>
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