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Overview

This quickstart shows you how to easily install a secure Kubernetes cluster on machines running Ubuntu 16.04, CentOS 7 or HypriotOS v1.0.1+. The installation uses a tool called kubeadm which is part of Kubernetes 1.4.

This process works with local VMs, physical servers and/or cloud servers. It is simple enough that you can easily integrate its use into your own automation (Terraform, Chef, Puppet, etc).

See the full kubeadm reference for information on all kubeadm command-line flags and for advice on automating kubeadm itself.

The kubeadm tool is currently in alpha but please try it out and give us feedback! Be sure to read the limitations; in particular note that kubeadm doesn’t have great support for automatically configuring cloud providers. Please refer to the specific cloud provider documentation or use another provisioning system.

kubeadm assumes you have a set of machines (virtual or real) that are up and running. It is designed to be part of a larger provisioning system - or just for easy manual provisioning. kubeadm is a great choice where you have your own infrastructure (e.g. bare metal), or where you have an existing orchestration system (e.g. Puppet) that you have to integrate with.

If you are not constrained, other tools build on kubeadm to give you complete clusters:

Prerequisites

  1. One or more machines running Ubuntu 16.04, CentOS 7 or HypriotOS v1.0.1+
  2. 1GB or more of RAM per machine (any less will leave little room for your apps)
  3. Full network connectivity between all machines in the cluster (public or private network is fine)

Objectives

Instructions

(1/4) Installing kubelet and kubeadm on your hosts

You will install the following packages on all the machines:

NOTE: If you already have kubeadm installed, you should do a apt-get update && apt-get upgrade or yum update to get the latest version of kubeadm. See the reference doc if you want to read about the different kubeadm releases

For each host in turn:

The kubelet is now restarting every few seconds, as it waits in a crashloop for kubeadm to tell it what to do.

Note: To disable SELinux by running setenforce 0 is required in order to allow containers to access the host filesystem, which is required by pod networks for example. You have to do this until kubelet can handle SELinux better.

(2/4) Initializing your master

The master is the machine where the “control plane” components run, including etcd (the cluster database) and the API server (which the kubectl CLI communicates with). All of these components run in pods started by kubelet.

Right now you can’t run kubeadm init twice without tearing down the cluster in between, see Tear down.

If you try to run kubeadm init and your machine is in a state that is incompatible with starting a Kubernetes cluster, kubeadm will warn you about things that might not work or it will error out for unsatisfied mandatory requirements.

To initialize the master, pick one of the machines you previously installed kubelet and kubeadm on, and run:

 # kubeadm init

Note: this will autodetect the network interface to advertise the master on as the interface with the default gateway. If you want to use a different interface, specify --api-advertise-addresses=<ip-address> argument to kubeadm init.

If you want to use flannel as the pod network, specify --pod-network-cidr=10.244.0.0/16 if you’re using the daemonset manifest below. However, please note that this is not required for any other networks besides Flannel.

Please refer to the kubeadm reference doc if you want to read more about the flags kubeadm init provides.

This will download and install the cluster database and “control plane” components. This may take several minutes.

The output should look like:

<master/tokens> generated token: "f0c861.753c505740ecde4c"
<master/pki> created keys and certificates in "/etc/kubernetes/pki"
<util/kubeconfig> created "/etc/kubernetes/kubelet.conf"
<util/kubeconfig> created "/etc/kubernetes/admin.conf"
<master/apiclient> created API client configuration
<master/apiclient> created API client, waiting for the control plane to become ready
<master/apiclient> all control plane components are healthy after 61.346626 seconds
<master/apiclient> waiting for at least one node to register and become ready
<master/apiclient> first node is ready after 4.506807 seconds
<master/discovery> created essential addon: kube-discovery
<master/addons> created essential addon: kube-proxy
<master/addons> created essential addon: kube-dns

Kubernetes master initialised successfully!

You can connect any number of nodes by running:

kubeadm join --token <token> <master-ip>

Make a record of the kubeadm join command that kubeadm init outputs. You will need this in a moment. The key included here is secret, keep it safe — anyone with this key can add authenticated nodes to your cluster.

The key is used for mutual authentication between the master and the joining nodes.

By default, your cluster will not schedule pods on the master for security reasons. If you want to be able to schedule pods on the master, for example if you want a single-machine Kubernetes cluster for development, run:

# kubectl taint nodes --all dedicated-
node "test-01" tainted
taint key="dedicated" and effect="" not found.
taint key="dedicated" and effect="" not found.

This will remove the “dedicated” taint from any nodes that have it, including the master node, meaning that the scheduler will then be able to schedule pods everywhere.

(3/4) Installing a pod network

You must install a pod network add-on so that your pods can communicate with each other.

It is necessary to do this before you try to deploy any applications to your cluster, and before kube-dns will start up. Note also that kubeadm only supports CNI based networks and therefore kubenet based networks will not work.

Several projects provide Kubernetes pod networks using CNI, some of which also support Network Policy. See the add-ons page for a complete list of available network add-ons.

You can install a pod network add-on with the following command:

# kubectl apply -f <add-on.yaml>

Please refer to the specific add-on installation guide for exact details. You should only install one pod network per cluster.

If you are on another architecture than amd64, you should use the flannel overlay network as described in the multi-platform section

NOTE: You can install only one pod network per cluster.

Once a pod network has been installed, you can confirm that it is working by checking that the kube-dns pod is Running in the output of kubectl get pods --all-namespaces.

And once the kube-dns pod is up and running, you can continue by joining your nodes.

(4/4) Joining your nodes

The nodes are where your workloads (containers and pods, etc) run. If you want to add any new machines as nodes to your cluster, for each machine: SSH to that machine, become root (e.g. sudo su -) and run the command that was output by kubeadm init. For example:

# kubeadm join --token <token> <master-ip>
<util/tokens> validating provided token
<node/discovery> created cluster info discovery client, requesting info from "http://138.68.156.129:9898/cluster-info/v1/?token-id=0f8588"
<node/discovery> cluster info object received, verifying signature using given token
<node/discovery> cluster info signature and contents are valid, will use API endpoints [https://138.68.156.129:443]
<node/csr> created API client to obtain unique certificate for this node, generating keys and certificate signing request
<node/csr> received signed certificate from the API server, generating kubelet configuration
<util/kubeconfig> created "/etc/kubernetes/kubelet.conf"

Node join complete:
* Certificate signing request sent to master and response
  received.
* Kubelet informed of new secure connection details.

Run 'kubectl get nodes' on the master to see this machine join.

A few seconds later, you should notice that running kubectl get nodes on the master shows a cluster with as many machines as you created.

Note that there currently isn’t a out-of-the-box way of connecting to the Master’s API Server via kubectl from a node. Read issue #35729 for more details.

(Optional) Controlling your cluster from machines other than the master

In order to get a kubectl on your laptop for example to talk to your cluster, you need to copy the KubeConfig file from your master to your laptop like this:

# scp root@<master ip>:/etc/kubernetes/admin.conf .
# kubectl --kubeconfig ./admin.conf get nodes

(Optional) Connecting to the API Server

If you want to connect to the API Server for viewing the dashboard (note: not deployed by default) from outside the cluster for example, you can use kubectl proxy:

# scp root@<master ip>:/etc/kubernetes/admin.conf .
# kubectl --kubeconfig ./admin.conf proxy

You can now access the API Server locally at http://localhost:8001/api/v1

(Optional) Installing a sample application

As an example, install a sample microservices application, a socks shop, to put your cluster through its paces. Note that this demo does only work on amd64. To learn more about the sample microservices app, see the GitHub README.

# kubectl create namespace sock-shop
# kubectl apply -n sock-shop -f "https://github.com/microservices-demo/microservices-demo/blob/master/deploy/kubernetes/complete-demo.yaml?raw=true"

You can then find out the port that the NodePort feature of services allocated for the front-end service by running:

# kubectl describe svc front-end -n sock-shop
Name:                   front-end
Namespace:              sock-shop
Labels:                 name=front-end
Selector:               name=front-end
Type:                   NodePort
IP:                     100.66.88.176
Port:                   <unset> 80/TCP
NodePort:               <unset> 31869/TCP
Endpoints:              <none>
Session Affinity:       None

It takes several minutes to download and start all the containers, watch the output of kubectl get pods -n sock-shop to see when they’re all up and running.

Then go to the IP address of your cluster’s master node in your browser, and specify the given port. So for example, http://<master_ip>:<port>. In the example above, this was 31869, but it is a different port for you.

If there is a firewall, make sure it exposes this port to the internet before you try to access it.

Tear down

Explore other add-ons

See the list of add-ons to explore other add-ons, including tools for logging, monitoring, network policy, visualization & control of your Kubernetes cluster.

What’s next

Feedback

kubeadm is multi-platform

kubeadm deb packages and binaries are built for amd64, arm and arm64, following the multi-platform proposal.

deb-packages are released for ARM and ARM 64-bit, but not RPMs (yet, reach out if there’s interest).

ARM had some issues when making v1.4, see #32517 #33485, #33117 and #33376.

However, thanks to the PRs above, kube-apiserver works on ARM from the v1.4.1 release, so make sure you’re at least using v1.4.1 when running on ARM 32-bit

The multiarch flannel daemonset can be installed this way.

# export ARCH=amd64
# curl -sSL "https://github.com/coreos/flannel/blob/master/Documentation/kube-flannel.yml?raw=true" | sed "s/amd64/${ARCH}/g" | kubectl create -f -

Replace ARCH=amd64 with ARCH=arm or ARCH=arm64 depending on the platform you’re running on. Note that the Raspberry Pi 3 is in ARM 32-bit mode, so for RPi 3 you should set ARCH to arm, not arm64.

Limitations

Please note: kubeadm is a work in progress and these limitations will be addressed in due course. Also you can take a look at the troubleshooting section in the reference document

  1. The cluster created here doesn’t have cloud-provider integrations by default, so for example it doesn’t work automatically with (for example) Load Balancers (LBs) or Persistent Volumes (PVs). To set up kubeadm with CloudProvider integrations (it’s experimental, but try), refer to the kubeadm reference document.

    Workaround: use the NodePort feature of services for exposing applications to the internet.

  2. The cluster created here has a single master, with a single etcd database running on it. This means that if the master fails, your cluster loses its configuration data and will need to be recreated from scratch. Adding HA support (multiple etcd servers, multiple API servers, etc) to kubeadm is still a work-in-progress.

    Workaround: regularly back up etcd. The etcd data directory configured by kubeadm is at /var/lib/etcd on the master.

  3. kubectl logs is broken with kubeadm clusters due to #22770.

    Workaround: use docker logs on the nodes where the containers are running as a workaround.

  4. The HostPort functionality does not work with kubeadm due to that CNI networking is used, see issue #31307.

    Workaround: use the NodePort feature of services instead, or use HostNetwork.

  5. A running firewalld service may conflict with kubeadm, so if you want to run kubeadm, you should disable firewalld until issue #35535 is resolved.

    Workaround: Disable firewalld or configure it to allow Kubernetes the pod and service cidrs.

  6. If you see errors like etcd cluster unavailable or misconfigured, it’s because of high load on the machine which makes the etcd container a bit unresponsive (it might miss some requests) and therefore kubelet will restart it. This will get better with etcd3.

    Workaround: Set failureThreshold in /etc/kubernetes/manifests/etcd.json to a larger value.

  7. If you are using VirtualBox (directly or via Vagrant), you will need to ensure that hostname -i returns a routable IP address (i.e. one on the second network interface, not the first one). By default, it doesn’t do this and kubelet ends-up using first non-loopback network interface, which is usually NATed. Workaround: Modify /etc/hosts, take a look at this Vagrantfile for how you this can be achieved.

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