Kubeadm /docs/admin/kubeadm.md cleanup, editing. (#5681)

* Update docs/admin/kubeadm.md (mostly 1.8 related).

This is Fabrizio's work, which I'm committing along with my edits (in a commit on top of this).

* A few of my own edits to clarify and clean up some Markdown.

docs/admin/kubeadm.md

@@ -14,7 +14,7 @@ This document provides information on how to use kubeadm's advanced options.
 * TOC
 {:toc}
 
-Running `kubeadm init` bootstraps a Kubernetes cluster. This consists of the
+Running `kubeadm init` bootstraps a Kubernetes master node. This consists of the
 following steps:
 
 1. kubeadm runs a series of pre-flight checks to validate the system state
@@ -24,44 +24,72 @@ following steps:
 
 1. kubeadm generates a token that additional nodes can use to register
    themselves with the master in future.  Optionally, the user can provide a
-   token.
+   token via `--token`, as described in the
+   [section on managing tokens](#manage-tokens) below.
 
 1. kubeadm generates a self-signed CA to provision identities for each component
    (including nodes) in the cluster.  It also generates client certificates to
    be used by various components.  If the user has provided their own CA by
-   dropping it in the cert directory (configured via `--cert-dir`, by default
+   dropping it in the cert directory configured via `--cert-dir`
-   `/etc/kubernetes/pki`), this step is skipped.
+   (`/etc/kubernetes/pki` by default) this step is skipped as described in the
+   [section on using custom certificates](#custom-certificates).
 
-1. kubeadm outputs a kubeconfig file for the master's kubelet to use to connect
+1. kubeadm writes kubeconfig files in `/etc/kubernetes/`  for
-   to the API server, as well as an additional kubeconfig file for cluster
+   the kubelet, the controller-manager and the scheduler to use to connect to the
-   administrators.
+   API server, each one with their respective identities, as well as an additional
+   kubeconfig file for administration.
 
-1. kubeadm generates Kubernetes static Pod manifests for the API server,
+1. kubeadm generates static Pod manifests for the API server,
-   controller manager and scheduler.  It places them in
+   controller manager and scheduler; in case an external etcd is not provided,
-   `/etc/kubernetes/manifests`. The kubelet watches this directory for Pods to
+   an additional static Pod manifest will be generated for etcd.
-   create on startup. These are the core components of Kubernetes. Once they are
-   up and running kubeadm can set up and manage any additional components.
 
-1. kubeadm "taints" the master node so that only control plane components will
+   Static Pod manifests are written in `/etc/kubernetes/manifests`; the kubelet
-   run there.  It also sets up the RBAC authorization system and writes a
+   watches this directory for Pods to create on startup, as described in
-   special ConfigMap that is used to bootstrap trust with the kubelets.
+   the [section about kubelet drop-in](#kubelet-drop-in).
+
+   Once control plane Pods are up and running kubeadm init sequence can continue.
+
+1. kubeadm "labels" and "taints" the master node so that only control plane
+   components will run there.
+
+1. Kubeadm makes all the necessary configurations for allowing node joining with the
+   [Bootstrap Tokens](https://kubernetes.io/docs/admin/bootstrap-tokens/) and
+   [TLS Bootstrap](https://kubernetes.io/docs/admin/kubelet-tls-bootstrapping/)
+   mechanism:
+
+   - Write a ConfigMap for making available all the information required
+     for joining and set up related RBAC access rules.
+
+   - Ensure access to the CSR signing API for bootstrap tokens.
+
+   - Configure auto approval for new CSR requests.
+
+   See [Securing your installation](#securing-more) for hardening.
 
 1. kubeadm installs add-on components via the API server.  Right now this is
    the internal DNS server and the kube-proxy DaemonSet.
 
+1. If `kubeadm init` is invoked with the alpha self-hosting feature enabled,
+   (`--feature-gates=SelfHosting=true`), the static Pod based control plane will
+   be transformed in a [self-hosed control plane](#self-hosting).
+
 Running `kubeadm join` on each node in the cluster consists of the following
 steps:
 
-1. kubeadm downloads root CA information from the API server.  By default, it
+1. kubeadm downloads necessary cluster information from the API server.
-   uses the bootstrap token and the CA key hash to verify the authenticity of
+   By default, it uses the bootstrap token and the CA key hash to verify the
-   that data. The root CA can also be discovered directly via a file or URL.
+   authenticity of that data. The root CA can also be discovered directly via a
+   file or URL.
 
-1. kubeadm creates a local key pair.  It prepares a certificate signing request
+1. Once the cluster information are known, kubelet can start the TLS bootstrapping
-   (CSR) and sends that off to the API server for signing.  The bootstrap token
+   process (in v.1.7 this step was managed by kubeadm).
-   is used to authenticate.  The control plane will sign this CSR requested
-   automatically.
 
-1. kubeadm configures the local kubelet to connect to the API server.
+   The TLS bootstrap uses the shared token to temporarily authenticate
+   with the Kubernetes Master to submit a certificate signing request (CSR); by
+   default the control plane will sign this CSR request automatically.
+
+1. Finally, kubeadm will configures the local kubelet to connect to the API
+   server with the definitive identity assigned to the node.
 
 ## Usage
 
@@ -69,9 +97,8 @@ Fields that support multiple values do so either with comma separation, or by
 specifying the flag multiple times.
 
 The kubeadm command line interface is currently in **beta**.  We are aiming to
-not break any scripted use of the main `kubeadm init` and `kubeadm join`.  The
+not break any scripted use of the main `kubeadm init` and `kubeadm join`.
-single exception here is the format of the kubeadm config file as detailed
+Exceptions to this are documented below.
-below.  That format is still considered alpha and may change.
 
 ### `kubeadm init`
 
@@ -116,18 +143,24 @@ flags that can be used to customise the Kubernetes installation.
   extended set of options including passing arbitrary command line flags to the
   control plane components.
 
-  **Note**: When providing configuration values using _both_ a configuration file
+  **Note**: Since 1.8, other flags are not allowed alongside `--config` except
-  and flags, the file will take precedence. For example, if a file exists with:
+  for flags used to define kubeadm behaviour (not configuration) such as
+  `--skip-preflight-checks`.
 
-  ```yaml
+- `--dry-run`
-  apiVersion: kubeadm.k8s.io/v1alpha1
-  kind: MasterConfiguration
-  token: 1234
-  ```
 
-  and the user ran `kubeadm init --config file.yaml --token 5678`,
+   This flag tells kubeadm to don't apply any changes; just output what would be done.
-  the chosen token value will be `1234`.
 
+- `--feature-gates`
+
+  A set of key=value pairs that describe feature gates for alpha/experimental
+  features. Options are:
+
+  - SelfHosting=true|false (ALPHA - default=false)
+
+  - StoreCertsInSecrets=true|false (ALPHA - default=false)
+
+  See [self-hosted control plane](#self-hosting) for more detail.
 
 - `--kubernetes-version` (default 'latest') the kubernetes version to initialise
 
@@ -138,6 +171,12 @@ flags that can be used to customise the Kubernetes installation.
   page](https://github.com/kubernetes/kubernetes/releases) for a full list of
   available versions.
 
+- `--node-name`
+
+  Allow to specify the node name, if something different than O.S. hostname should be used e.g. in case of Amazon EC2 instances.
+
+  The node-name is also added to the certificate that the API Server uses.
+
 - `--pod-network-cidr`
 
   For certain networking solutions the Kubernetes master can also play a role in
@@ -181,6 +220,11 @@ flags that can be used to customise the Kubernetes installation.
   before making any changes. Advanced users can use this flag to bypass these if
   necessary.
 
+- `--skip-token-print`
+
+  By default, kubeadm prints the token at the end of the init procedure. Advanced
+  users can use this flag to bypass these if necessary.
+
 - `--token`
 
   By default, `kubeadm init` automatically generates the token used to initialise
@@ -242,12 +286,6 @@ Here's an example on how to use it:
 
   Extended options are specified in the [kubeadm specific config file](#config-file).
 
-- `--skip-preflight-checks`
-
-  By default, kubeadm runs a series of preflight checks to validate the system
-  before making any changes. Advanced users can use this flag to bypass these if
-  necessary.
-
 - `--discovery-file`
 
   A local file path or HTTPS URL.  The file specified must be a kubeconfig file
@@ -301,6 +339,12 @@ Here's an example on how to use it:
   [security tradeoffs](#security-model) involved in skipping this verification
   (which may or may not be appropriate in your environment).
 
+- `--node-name`
+
+  Specify the Node name. The default is to use the OS hostname. This is useful
+  on some cloud providers such as AWS. This name is also added to the node's
+  TLS certificate.
+
 - `--tls-bootstrap-token`
 
   The token used to authenticate to the API server for the purposes of TLS
@@ -312,6 +356,47 @@ Here's an example on how to use it:
   `--tls-bootstrap-token`.  This option specifies the same token for both.  Other
   flags override this flag if present.
 
+- `--skip-preflight-checks`
+
+  By default, kubeadm runs a series of preflight checks to validate the system
+  before making any changes. Advanced users can use this flag to bypass these if
+  necessary.
+
+### `kubeadm completion`
+
+Output shell completion code for the specified shell (bash or zsh).
+
+### `kubeadm config`
+
+Kubeadm v1.8.0+ automatically creates a ConfigMap with all the parameters
+used during `kubeadm init`.
+
+If you initialized your cluster using kubeadm v1.7.x or lower, you must use
+the `kubeadm config upload` command to create this ConfigMap in order
+for `kubeadm upgrade` to be able to configure your upgraded cluster correctly.
+
+### `kubeadm reset`
+
+Reverts any changes made to this host by `kubeadm init` or `kubeadm join`.
+
+### `kubeadm token`
+
+Manage tokens on a running cluster. See [managing tokens](#manage-tokens) below
+for further details.
+
+### `kubeadm alpha phases`
+
+**WARNING:** While kubeadm command line interface is in beta, commands under
+this entry is still considered alpha and may change in future versions.
+
+`kubeadm phase` introduces a set of kubeadm CLI commands allowing to invoke
+individually each phase of the kubeadm init sequence; phases provide a reusable
+and composable API/toolbox for building your own automated cluster installer.
+
+**Options for `kubeadm phases`:**
+
+Each kubeadm phase exposes a subset of relevant options from `kubeadm init`.
+
 ## Using kubeadm with a configuration file {#config-file}
 
 **WARNING:** While kubeadm command line interface is in beta, the config file is
@@ -337,12 +422,18 @@ etcd:
   caFile: <path|string>
   certFile: <path|string>
   keyFile: <path|string>
+  dataDir: <path|string>
+  extraArgs:
+    <argument>: <value|string>
+    <argument>: <value|string>
+  image: <string>
 networking:
   dnsDomain: <string>
   serviceSubnet: <cidr>
   podSubnet: <cidr>
 kubernetesVersion: <string>
 cloudProvider: <string>
+nodeName: <string>
 authorizationModes:
 - <authorizationMode1|string>
 - <authorizationMode2|string>
@@ -362,6 +453,11 @@ apiServerCertSANs:
 - <name1|string>
 - <name2|string>
 certificatesDir: <string>
+imageRepository: <string>
+unifiedControlPlaneImage: <string>
+featureGates:
+  <feature>: <bool>
+  <feature>: <bool>
 ```
 In addition, if authorizationMode is set to `ABAC`, you should write the config to `/etc/kubernetes/abac_policy.json`.
 However, if authorizationMode is set to `Webhook`, you should write the config to `/etc/kubernetes/webhook_authz.conf`.
@@ -377,10 +473,16 @@ discoveryToken: <string>
 discoveryTokenAPIServers:
 - <address|string>
 - <address|string>
+nodeName: <string>
 tlsBootstrapToken: <string>
+token: <string>
+discoveryTokenCACertHashes:
+- <SHA-256 hash|string>
+- <SHA-256 hash|string>
+discoveryTokenUnsafeSkipCAVerification: <bool>
 ```
 
-## Securing your installation even more
+## Securing your installation even more {#securing-more}
 
 The defaults for kubeadm may not work for everyone. This section documents how to tighten up a kubeadm install
 at the cost of some usability.
@@ -609,19 +711,26 @@ using kubeadm.
 
 ## Use kubeadm with other CRI runtimes
 
-Since [Kubernetes 1.6 release](https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG.md#node-components-1), Kubernetes container runtimes have been transferred to using CRI by default. Currently, the build-in container runtime is Docker which is enabled by build-in `dockershim` in `kubelet`.
+Since [Kubernetes 1.6 release](https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG.md#node-components-1),
+Kubernetes container runtimes have been transferred to using CRI by default.
+Currently, the build-in container runtime is Docker which is enabled by built-in
+`dockershim` in `kubelet`.
 
-Using other CRI based runtimes with kubeadm is very simple, and currently supported runtimes are:
+Using other CRI based runtimes with kubeadm is very simple, and currently
+supported runtimes are:
 
 - [cri-o](https://github.com/kubernetes-incubator/cri-o)
 - [frakti](https://github.com/kubernetes/frakti)
 - [rkt](https://github.com/kubernetes-incubator/rktlet)
 
-After you have successfully installed `kubeadm` and `kubelet`, please follow these two steps:
+After you have successfully installed `kubeadm` and `kubelet`, please follow
+these two steps:
 
-1. Install runtime shim on every node. You will need to follow the installation document in the runtime shim project listing above.
+1. Install runtime shim on every node. You will need to follow the installation
+   document in the runtime shim project listing above.
 
-2. Configure kubelet to use remote CRI runtime. Please remember to change `RUNTIME_ENDPOINT` to your own value like `/var/run/{your_runtime}.sock`:
+1. Configure kubelet to use remote CRI runtime. Please remember to change
+   `RUNTIME_ENDPOINT` to your own value like `/var/run/{your_runtime}.sock`:
 
 ```shell
   $ cat > /etc/systemd/system/kubelet.service.d/20-cri.conf <<EOF
@@ -630,7 +739,22 @@ EOF
   $ systemctl daemon-reload
 ```
 
-Now `kubelet` is ready to use the specified CRI runtime, and you can continue with `kubeadm init` and `kubeadm join` workflow to deploy Kubernetes cluster.
+Now `kubelet` is ready to use the specified CRI runtime, and you can continue
+with `kubeadm init` and `kubeadm join` workflow to deploy Kubernetes cluster.
+
+## Using custom images {#custom-images}
+
+By default, kubeadm will pull images from `gcr.io/google_containers`, unless
+requested kubernetes version is a ci version; in this case
+`gcr.io/kubernetes-ci-image` will be used.
+
+This behaviour can be overridden by [using kubeadm with a configuration file](#config-file).
+Allowed customization are:
+- provide an alternative `imageRepository` to be used instead of
+  `gcr.io/google_containers` (NB. does not works for ci version)
+- provide an `unifiedControlPlaneImage` to be used instead of single images
+  for control plane components
+- provide an `etcd.image` name to be used
 
 ## Running kubeadm without an internet connection
 
@@ -655,7 +779,7 @@ Here `v1.7.x` means the "latest patch release of the v1.7 branch".
 
 `${ARCH}` can be one of: `amd64`, `arm`, `arm64`, `ppc64le` or `s390x`.
 
-## Managing the kubeadm drop-in file for the kubelet
+## Managing the kubeadm drop-in file for the kubelet {#kubelet-drop-in}
 
 The kubeadm deb package ships with configuration for how the kubelet should
 be run. Note that the `kubeadm` CLI command will never touch this drop-in file.
@@ -751,15 +875,15 @@ help to fully automate this process in the future.
 
 ## Environment variables
 
+**Note:** These environment variables are deprecated and will stop functioning in v1.8!
+
 There are some environment variables that modify the way that kubeadm works.
 Most users will have no need to set these. These environment variables are a
 short-term solution, eventually they will be integrated in the kubeadm
 configuration file.
 
-**Note:** These environment variables are deprecated and will stop functioning in v1.8!
-
 | Variable               | Default                                       | Description                              |
-| --- | --- | --- |
+| ---------------------- | --------------------------------------------- | ---------------------------------------- |
 | `KUBE_KUBERNETES_DIR`  | `/etc/kubernetes`                             | Where most configuration files are written to and read from |
 | `KUBE_HYPERKUBE_IMAGE` |                                               | If set, use a single hyperkube image with this name. If not set, individual images per server component will be used. |
 | `KUBE_ETCD_IMAGE`      | `gcr.io/google_containers/etcd-<arch>:3.0.17` | The etcd container image to use. |
@@ -803,7 +927,7 @@ export no_proxy="localhost,127.0.0.1,localaddress,.localdomain.com,example.com,1
 Remember to change `proxy_ip` and add a kube master node IP address to
 `no_proxy`.
 
-## Using custom certificates
+## Using custom certificates {#custom-certificates}
 
 By default kubeadm will generate all the certificates needed for a cluster to run.
 You can override this behaviour by providing your own certificates.
@@ -820,6 +944,11 @@ This means you can, for example, prepopulate `/etc/kubernetes/pki/ca.crt`
 and `/etc/kubernetes/pki/ca.key` with an existing CA, which then will be used
 for signing the rest of the certs.
 
+Only for the CA, it is possible to provide the `ca.crt` file but not the `ca.key`
+file; if all other certificates and kubeconfig files already are in place kubeadm
+recognise this condition and activates the so called "ExternalCA" mode, which also
+implies the csrsignercontroller in controller-manager won't be started.
+
 ## Self-hosting the Kubernetes control plane  {#self-hosting}
 As of 1.8, kubeadm can experimentally create a _self-hosted_ Kubernetes control
 plane. This means that key components such as the API server, controller