Add CRI installation instructions page

Added cri-installation page with CRI installation instructions
Referenced it from kubeadm-init and install-kubeadm pages.

Signed-off-by: Vince Prignano <vince@vincepri.com>
Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>

content/en/docs/reference/setup-tools/kubeadm/kubeadm-init.md

@@ -381,6 +381,8 @@ Other CRI-based runtimes include:
 - [frakti](https://github.com/kubernetes/frakti)
 - [rkt](https://github.com/kubernetes-incubator/rktlet)
 
+Refer to the [CRI installation instructions](/docs/setup/cri/cri-installation/) for more information.
+
 After you have successfully installed `kubeadm` and `kubelet`, execute
 these two additional steps:
 

content/en/docs/setup/cri/_index.md

@@ -0,0 +1,4 @@
+---
+title: Kubernetes CRI
+weight: 30
+---

content/en/docs/setup/cri/cri-installation.md

@@ -0,0 +1,141 @@
+---
+reviewers:
+- vincepri
+- bart0sh
+title: CRI installation
+content_template: templates/concept
+weight: 100
+---
+{{% capture overview %}}
+Since v1.6.0, Kubernetes has enabled the use of CRI, Container Runtime Interface, by default.
+This page contains installation instruction for various runtimes.
+
+{{% /capture %}}
+
+{{% capture body %}}
+
+### Containerd
+
+This section contains the necessary steps to use `containerd` as CRI with kubeadm.
+
+#### Prerequisites
+
+```shell
+modprobe overlay
+modprobe br_netfilter
+
+# Setup required sysctl params, these persist across reboots.
+cat > /etc/sysctl.d/99-kubernetes-cri.conf <<EOF
+net.bridge.bridge-nf-call-iptables  = 1
+net.ipv4.ip_forward                 = 1
+net.bridge.bridge-nf-call-ip6tables = 1
+EOF
+
+sysctl --system
+```
+
+{{< tabs name="tab-cri-containerd-installation" >}}
+{{< tab name="Ubuntu 16.04+" codelang="bash" >}}
+apt-get install -y libseccomp2
+{{< /tab >}}
+{{< tab name="CentOS/RHEL 7.4+" codelang="bash" >}}
+yum install -y libseccomp
+{{< /tab >}}
+{{< /tabs >}}
+
+#### Install containerd
+
+[Containerd releases](https://github.com/containerd/containerd/releases) are published regularly, the values below are hardcoded to the latest version available at the time of writing. Please check for newer versions and hashes [here](https://storage.googleapis.com/cri-containerd-release).
+
+```shell
+# Export required environment variables.
+export CONTAINERD_VERSION="1.1.2"
+export CONTAINERD_SHA256="d4ed54891e90a5d1a45e3e96464e2e8a4770cd380c21285ef5c9895c40549218"
+
+# Download containerd tar.
+wget https://storage.googleapis.com/cri-containerd-release/cri-containerd-${CONTAINERD_VERSION}.linux-amd64.tar.gz
+
+# Check hash.
+echo "${CONTAINERD_SHA256} cri-containerd-${CONTAINERD_VERSION}.linux-amd64.tar.gz" | sha256sum --check -
+
+# Unpack.
+tar --no-overwrite-dir -C / -xzf cri-containerd-${CONTAINERD_VERSION}.linux-amd64.tar.gz
+
+# Start containerd.
+systemctl start containerd
+```
+
+### Docker
+
+{{< tabs name="tab-cri-docker-installation" >}}
+{{< tab name="Ubuntu 16.04" codelang="bash" >}}
+# Install prerequisites.
+apt-get install apt-transport-https ca-certificates curl software-properties-common
+
+# Download GPG key.
+curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
+
+# Add docker apt repository.
+add-apt-repository \
+   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
+   $(lsb_release -cs) \
+   stable"
+
+# Install docker.
+apt-get update && apt-get install docker-ce=17.03.2~ce-0~ubuntu-xenial
+
+# Setup daemon.
+cat > /etc/docker/daemon.json <<EOF
+{
+  "exec-opts": ["native.cgroupdriver=systemd"],
+  "log-driver": "json-file",
+  "log-opts": {
+    "max-size": "100m"
+  },
+  "storage-driver": "overlay2"
+}
+EOF
+
+mkdir -p /etc/systemd/system/docker.service.d
+
+# Restart docker.
+systemctl daemon-reload
+systemctl restart docker
+{{< /tab >}}
+{{< tab name="CentOS/RHEL 7.4+" codelang="bash" >}}
+# Install prerequisites.
+yum install yum-utils device-mapper-persistent-data lvm2
+
+# Add docker repository.
+yum-config-manager \
+    --add-repo \
+    https://download.docker.com/linux/centos/docker-ce.repo
+
+# Install docker.
+apt-get update && yum install docker-ce-17.03.2.ce
+
+# Setup daemon.
+cat > /etc/docker/daemon.json <<EOF
+{
+  "exec-opts": ["native.cgroupdriver=systemd"],
+  "log-driver": "json-file",
+  "log-opts": {
+    "max-size": "100m"
+  },
+  "storage-driver": "overlay2",
+  "storage-opts": [
+    "overlay2.override_kernel_check=true"
+  ]
+}
+EOF
+
+mkdir -p /etc/systemd/system/docker.service.d
+
+# Restart docker.
+systemctl daemon-reload
+systemctl restart docker
+{{< /tab >}}
+{{< /tabs >}}
+
+
+{{% /capture %}}

content/en/docs/setup/independent/install-kubeadm.md

@@ -79,7 +79,13 @@ The pod network plugin you use (see below) may also require certain ports to be
 open. Since this differs with each pod network plugin, please see the
 documentation for the plugins about what port(s) those need.
 
-## Installing Docker
+## Installing runtime
+
+Since v1.6.0, Kubernetes has enabled the use of CRI, Container Runtime Interface, by default.
+The container runtime used by default is Docker, which is enabled through the built-in
+`dockershim` CRI implementation inside of the `kubelet`.
+
+### Installing Docker
 
 On each of your machines, install Docker.
 Version 17.03 is recommended, but 1.11, 1.12 and 1.13 are known to work as well.
@@ -131,6 +137,17 @@ systemctl enable docker && systemctl start docker
 Refer to the [official Docker installation guides](https://docs.docker.com/engine/installation/)
 for more information.
 
+### Installing other CRI runtime
+
+Other CRI-based runtimes include:
+
+- [cri-containerd](https://github.com/containerd/cri-containerd)
+- [cri-o](https://github.com/kubernetes-incubator/cri-o)
+- [frakti](https://github.com/kubernetes/frakti)
+- [rkt](https://github.com/kubernetes-incubator/rktlet)
+
+Refer to the [CRI installation instructions](/docs/setup/cri/cri-installation/) for more information.
+
 ## Installing kubeadm, kubelet and kubectl
 
 You will install these packages on all of your machines: