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Installing Kubernetes on Linux with kubeadm

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.

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 large 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, there are some other tools built 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: Disabling 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 and the following images are required and will be automatically pulled by kubelet if they are absent while kubeadm init is initializing your master:

gcr.io/google_containers/kube-proxy-amd64                v1.5.3         
gcr.io/google_containers/kube-controller-manager-amd64   v1.5.3         
gcr.io/google_containers/kube-scheduler-amd64            v1.5.3         
gcr.io/google_containers/kube-apiserver-amd64            v1.5.3         
gcr.io/google_containers/etcd-amd64                      3.0.14-kubeadm 
gcr.io/google_containers/kube-discovery-amd64            1.0            
gcr.io/google_containers/pause-amd64                     3.0

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:

[kubeadm] WARNING: kubeadm is in alpha, please do not use it for production clusters.
[preflight] Running pre-flight checks
[init] Using Kubernetes version: v1.5.1
[tokens] Generated token: "064158.548b9ddb1d3fad3e"
[certificates] Generated Certificate Authority key and certificate.
[certificates] Generated API Server key and certificate
[certificates] Generated Service Account signing keys
[certificates] Created keys and certificates in "/etc/kubernetes/pki"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/kubelet.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/admin.conf"
[apiclient] Created API client, waiting for the control plane to become ready
[apiclient] All control plane components are healthy after 61.317580 seconds
[apiclient] Waiting for at least one node to register and become ready
[apiclient] First node is ready after 6.556101 seconds
[apiclient] Creating a test deployment
[apiclient] Test deployment succeeded
[token-discovery] Created the kube-discovery deployment, waiting for it to become ready
[token-discovery] kube-discovery is ready after 6.020980 seconds
[addons] Created essential addon: kube-proxy
[addons] Created essential addon: kube-dns

Your Kubernetes master has initialized successfully!

You should now deploy a pod network to the cluster.
Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:
    http://kubernetes.io/docs/admin/addons/

You can now join any number of machines by running the following on each node:

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:

# MASTER_NODE="actual_master_node_name"
# TAINT_KEY=$(kubectl get no ${MASTER_NODE} --template="")
# kubectl taint nodes ${MASTER_NODE} ${TAINT_KEY}-

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.

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.

You may have trouble in the configuration if you see the following statuses

NAMESPACE     NAME                              READY     STATUS              RESTARTS   AGE
kube-system   canal-node-f0lqp                  2/3       RunContainerError   2          48s
kube-system   canal-node-77d0h                  2/3       CrashLoopBackOff    3          3m
kube-system   kube-dns-2924299975-7q1vq         0/4       ContainerCreating   0          15m

The three statuses RunContainerError and CrashLoopBackOff and ContainerCreating are very common.

To help diagnose what happened, you can use the following command to check what is in the logs:

kubectl describe -n kube-system po {YOUR_POD_NAME}

Do not use kubectl logs. You will get the following error:

# kubectl logs -n kube-system canal-node-f0lqp
Error from server (BadRequest): the server rejected our request for an unknown reason (get pods canal-node-f0lqp)

The kubectl describe command gives you more details about the logs

# kubectl describe -n kube-system po kube-dns-2924299975-1l2t7
  2m        2m        1    {kubelet nac}    spec.containers{flannel}        Warning        Failed        Failed to start container with docker id 927e7ccdc32b with error: Error response from daemon: {"message":"chown /etc/resolv.conf: operation not permitted"}

Or 6m 1m 191 {kubelet nac} Warning FailedSync Error syncing pod, skipping: failed to "SetupNetwork" for "kube-dns-2924299975-1l2t7_kube-system" with SetupNetworkError: "Failed to setup network for pod \"kube-dns-2924299975-1l2t7_kube-system(dee8ef21-fbcb-11e6-ba19-38d547e0006a)\" using network plugins \"cni\": open /run/flannel/subnet.env: no such file or directory; Skipping pod"

You can then search Google for the error messages, which may help you find a solution.

(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>
[kubeadm] WARNING: kubeadm is in alpha, please do not use it for production clusters.
[preflight] Running pre-flight checks
[preflight] Starting the kubelet service
[tokens] Validating provided token
[discovery] Created cluster info discovery client, requesting info from "http://192.168.x.y:9898/cluster-info/v1/?token-id=f11877"
[discovery] Cluster info object received, verifying signature using given token
[discovery] Cluster info signature and contents are valid, will use API endpoints [https://192.168.x.y:6443]
[bootstrap] Trying to connect to endpoint https://192.168.x.y:6443
[bootstrap] Detected server version: v1.5.1
[bootstrap] Successfully established connection with endpoint "https://192.168.x.y:6443"
[csr] Created API client to obtain unique certificate for this node, generating keys and certificate signing request
[csr] Received signed certificate from the API server:
Issuer: CN=kubernetes | Subject: CN=system:node:yournode | CA: false
Not before: 2016-12-15 19:44:00 +0000 UTC Not After: 2017-12-15 19:44:00 +0000 UTC
[csr] Generating kubelet configuration
[kubeconfig] Wrote KubeConfig file to disk: "/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.

(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: the dashboard isn’t 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 30001, 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).

Cloudprovider integrations (experimental)

Enabling specific cloud providers is a common request, this currently requires manual configuration and is therefore not yet supported. If you wish to do so, edit the kubeadm dropin for the kubelet service (/etc/systemd/system/kubelet.service.d/10-kubeadm.conf) on all nodes, including the master. If your cloud provider requires any extra packages installed on host, for example for volume mounting/unmounting, install those packages.

Specify the --cloud-provider flag to kubelet and set it to the cloud of your choice. If your cloudprovider requires a configuration file, create the file /etc/kubernetes/cloud-config on every node. The exact format and content of that file depends on the requirements imposed by your cloud provider. If you use the /etc/kubernetes/cloud-config file, you must append it to the kubelet arguments as follows: --cloud-config=/etc/kubernetes/cloud-config

Lastly, run kubeadm init --cloud-provider=xxx to bootstrap your cluster with cloud provider features.

This workflow is not yet fully supported, however we hope to make it extremely easy to spin up clusters with cloud providers in the future. (See this proposal for more information) The Kubelet Dynamic Settings feature may also help to fully automate this process in the future.

Limitations

Please note: kubeadm is a work in progress and these limitations will be addressed in due course.

  1. 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.

  2. The HostPort and HostIP 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.

  3. Some users on RHEL/CentOS 7 have reported issues with traffic being routed incorrectly due to iptables being bypassed. You should ensure net.bridge.bridge-nf-call-iptables is set to 1 in your sysctl config, eg.

    console # cat /etc/sysctl.d/k8s.conf net.bridge.bridge-nf-call-ip6tables = 1 net.bridge.bridge-nf-call-iptables = 1

  4. There is no built-in way of fetching the token easily once the cluster is up and running, but here is a kubectl command you can copy and paste that will print out the token for you:

    console # kubectl -n kube-system get secret clusterinfo -o yaml | grep token-map | awk '{print $2}' | base64 --decode | sed "s|{||g;s|}||g;s|:|.|g;s/\"//g;" | xargs echo

  5. 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 this can be achieved.

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