Setup

Instructions for setting up a Kubernetes cluster.

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Using kubeadm to Create a Cluster

This quickstart shows you how to easily install a 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. As of v1.6, kubeadm aims to create a secure cluster out of the box via mechanisms such as RBAC.

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.

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 other higher-level tools built to give you complete clusters:

kubeadm Maturity

Aspect Maturity Level
Command line UX beta
Config file alpha
Selfhosting alpha
kubeadm alpha commands alpha
Implementation alpha

The experience for the command line is currently in beta and we are trying hard not to change command line flags and break that flow. Other parts of the experience are still under active development. Specifically, kubeadm relies on some features (bootstrap tokens, cluster signing), that are still considered alpha. The implementation may change as the tool evolves to support easy upgrades and high availability (HA). Any commands under kubeadm alpha (not documented here) are, of course, alpha.

Be sure to read the limitations. Specifically, configuring cloud providers is difficult. Upgrades are also not well documented or particularly easy.

Before you begin

  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 kubeadm on your hosts

See Installing kubeadm

(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).

To initialize the master, pick one of the machines you previously installed 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 --apiserver-advertise-address=<ip-address> argument to kubeadm init.

There are pod network implementations where the master also plays a role in allocating a set of network address space for each node. When using flannel as the pod network (described in step 3), specify --pod-network-cidr=10.244.0.0/16. 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.

kubeadm init will first run a series of prechecks to ensure that the machine is ready to run Kubernetes. It will expose warnings and exit on errors. It will then download and install the cluster database and “control plane” components. This may take several minutes.

You can’t run kubeadm init twice without tearing down the cluster in between, see Tear Down.

The output should look like:

[kubeadm] WARNING: kubeadm is in beta, please do not use it for production clusters.
[init] Using Kubernetes version: v1.6.0
[init] Using Authorization mode: RBAC
[preflight] Running pre-flight checks
[preflight] Starting the kubelet service
[certificates] Generated CA certificate and key.
[certificates] Generated API server certificate and key.
[certificates] API Server serving cert is signed for DNS names [kubeadm-master kubernetes kubernetes.default kubernetes.default.svc kubernetes.default.svc.cluster.local] and IPs [10.96.0.1 10.138.0.4]
[certificates] Generated API server kubelet client certificate and key.
[certificates] Generated service account token signing key and public key.
[certificates] Generated front-proxy CA certificate and key.
[certificates] Generated front-proxy client certificate and key.
[certificates] Valid certificates and keys now exist in "/etc/kubernetes/pki"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/admin.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/kubelet.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/controller-manager.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/scheduler.conf"
[apiclient] Created API client, waiting for the control plane to become ready
[apiclient] All control plane components are healthy after 16.772251 seconds
[apiclient] Waiting for at least one node to register and become ready
[apiclient] First node is ready after 5.002536 seconds
[apiclient] Test deployment succeeded
[token] Using token: <token>
[apiconfig] Created RBAC rules
[addons] Created essential addon: kube-proxy
[addons] Created essential addon: kube-dns

Your Kubernetes master has initialized successfully!

To start using your cluster, you need to run (as a regular user):

  sudo cp /etc/kubernetes/admin.conf $HOME/
  sudo chown $(id -u):$(id -g) $HOME/admin.conf
  export KUBECONFIG=$HOME/admin.conf

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
as root:

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

Make a record of the kubeadm join command that kubeadm init outputs. You will need this in a moment.

The token is used for mutual authentication between the master and the joining nodes. The token included here is secret, keep it safe — anyone with this token can add authenticated nodes to your cluster. These tokens can be listed, created and deleted with the kubeadm token command. See the reference guide.

Master Images

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:

Image Name Version
gcr.io/google_containers/kube-apiserver-amd64 v1.6.0
gcr.io/google_containers/kube-controller-manager-amd64 v1.6.0
gcr.io/google_containers/kube-scheduler-amd64 v1.6.0
gcr.io/google_containers/kube-proxy-amd64 v1.6.0
gcr.io/google_containers/etcd-amd64 3.0.17
gcr.io/google_containers/pause-amd64 3.0
gcr.io/google_containers/k8s-dns-sidecar-amd64 1.14.1
gcr.io/google_containers/k8s-dns-kube-dns-amd64 1.14.1
gcr.io/google_containers/k8s-dns-dnsmasq-nanny-amd64 1.14.1

Master Isolation

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, e.g. a single-machine Kubernetes cluster for development, run:

kubectl taint nodes --all node-role.kubernetes.io/master-

With output looking something like:

node "test-01" tainted
taint key="dedicated" and effect="" not found.
taint key="dedicated" and effect="" not found.

This will remove the node-role.kubernetes.io/master 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.

The network must be deployed before any applications. Also, kube-dns, a helper service, will not start up before a network is installed. kubeadm only supports Container Network Interface (CNI) based networks (and does not support kubenet).

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.

New for Kubernetes 1.6: kubeadm 1.6 sets up a more secure cluster by default. As such it uses RBAC to grant limited privileges to workloads running on the cluster. This includes networking integrations. As such, ensure that you are using a network system that has been updated to run with 1.6 and RBAC.

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 or Weave Net overlay networks 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.

If your network is not working or kube-dns is not in the Running state, check out the troubleshooting section below.

(4/4) Joining your nodes

The nodes are where your workloads (containers and pods, etc) run. To add new nodes to your cluster do the following for each machine:

The output should look something like:

[kubeadm] WARNING: kubeadm is in beta, please do not use it for production clusters.
[preflight] Running pre-flight checks
[discovery] Trying to connect to API Server "10.138.0.4:6443"
[discovery] Created cluster-info discovery client, requesting info from "https://10.138.0.4:6443"
[discovery] Cluster info signature and contents are valid, will use API Server "https://10.138.0.4:6443"
[discovery] Successfully established connection with API Server "10.138.0.4:6443"
[bootstrap] Detected server version: v1.6.0-beta.3
[bootstrap] The server supports the Certificates API (certificates.k8s.io/v1beta1)
[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, generating KubeConfig...
[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 this node in the output from kubectl get nodes when run on the master.

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

In order to get a kubectl on some other computer (e.g. laptop) to talk to your cluster, you need to copy the kubeconfig file from your master to your workstation like this:

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

Note: If you are using GCE, instances, by default, disable ssh access for root. First log in to the machine, copy the file someplace that can be accessed and then use gcloud compute copy-files

(Optional) Connecting to the API Server

If you want to connect to the API Server from outside the cluster 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

Now it is time to take your new cluster for a test drive. Sock Shop is a sample microservices application that shows how to run and connect a set of services on Kubernetes. To learn more about the sample microservices app, see the GitHub README.

Note that the Sock Shop demo only works on amd64.

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 -n sock-shop get svc front-end

Output:

NAME        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
front-end   10.110.250.153   <nodes>       80:30001/TCP   59s

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 may be 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.

To uninstall the socks shop, run kubectl delete namespace sock-shop on the master.

Tear down

To undo what kubeadm did, you should first drain the node and make sure that the node is empty before shutting it down.

Talking to the master with the appropriate credentials, run:

kubectl drain <node name> --delete-local-data --force --ignore-daemonsets
kubectl delete node <node name>

Then, on the node being removed, reset all kubeadm installed state:

kubeadm reset

If you wish to start over simply run kubeadm init or kubeadm join with the appropriate arguments.

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/rpm packages and binaries are built for amd64, arm64, armhfp, ppc64el, and s390x following the multi-platform proposal.

Currently, only the pod networks flannel and Weave Net work on multiple architectures. For Weave Net just use its standard install.

Flannel requires special installation instructions:

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.

Cloudprovider integrations (experimental)

Enabling specific cloud providers is a common request. This currently requires manual configuration and is therefore not yet fully 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

Next, specify the cloud provider in the kubeadm config file. Create a file called kubeadm.conf with the following contents:

kind: MasterConfiguration
apiVersion: kubeadm.k8s.io/v1alpha1
cloudProvider: <cloud provider>

Lastly, run kubeadm init --config=kubeadm.conf to bootstrap your cluster with the cloud provider.

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.

    cat /etc/sysctl.d/k8s.conf
    

    Should have:

    net.bridge.bridge-nf-call-ip6tables = 1
    net.bridge.bridge-nf-call-iptables = 1
    
  4. Users can list, create and delete tokens using the kubeadm token command. See the reference guide for details.

  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.

Troubleshooting

Pod Network Troubleshooting

You may have trouble in the configuration if you see the following statuses. This example is for canal but there may be similar errors for other pod network systems.

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 as they only work with Pods that have started. If you run:

kubectl logs -n kube-system canal-node-f0lqp

You will got the following error:

Error from server (BadRequest): the server rejected our request for an unknown reason (get pods canal-node-f0lqp)

The kubectl describe comand gives you more details about what went wrong.

kubectl describe -n kube-system po kube-dns-2924299975-1l2t7

The events should show something like this:

  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 this:

  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"

A web search on the error message may help narrow down the issue. Or communicate the errors you are seeing to the community/company that provides the pod network implementation you are using.

Installing kubeadm 1.5

This section covers the previous version, kubeadm 1.5. It is still available but is a little tricky to get to. Also note that the command line options and other configuration parameters have changed.

As root, run the following. This is very similar to the regular instructions except for pinning the versions. Note that, due to some unfortunate version strings, kubeadm isn’t indexed in the repos and the packages must be downloaded and installed directly.

Ubuntu

apt-get update && apt-get install -y apt-transport-https
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
cat <<EOF >/etc/apt/sources.list.d/kubernetes.list
deb http://apt.kubernetes.io/ kubernetes-xenial main
EOF
apt-get update

# 1.5.6 does exist in the repo but it has a hard depenedency on a newer kubernetes-cni.  Use 1.5.3 instead.
sudo apt-get -y install kubectl=1.5.3-00 kubelet=1.5.3-00 kubernetes-cni=0.3.0.1-07a8a2-00

# Versioning strangeness for how we packaged kubeadm pre-1.6 means that the version number
# says 1.6.0-alpha even though it is the 1.5 version of kubeadm.  Because of how this sorts,
# we cannot keep this deb in the repo.  Download it manually and install it.
curl -Lo /tmp/old-kubeadm.deb https://apt.k8s.io/pool/kubeadm_1.6.0-alpha.0.2074-a092d8e0f95f52-00_amd64_0206dba536f698b5777c7d210444a8ace18f48e045ab78687327631c6c694f42.deb
sudo dpkg -i /tmp/old-kubeadm.deb
sudo apt-get install -f

# Hold these packages back so that we don't accidentally upgrade them.
sudo apt-mark hold kubeadm kubectl kubelet kubernetes-cni

CentOS

cat <<EOF > /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=http://yum.kubernetes.io/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg
        https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOF

setenforce 0

# 1.5.4 is the latest previous version in the repo.  Because of messed up
# versioning in the 1.5 release, kubeadm is no longer indexed in the repos
# so we have to refer to the RPM directly.
sudo yum -y install \
  yum-versionlock \
  docker \
  kubectl-1.5.4-0 \
  kubelet-1.5.4-0 \
  kubernetes-cni-0.3.0.1-0.07a8a2 \
  http://yum.kubernetes.io/pool/082436e6e6cad1852864438b8f98ee6fa3b86b597554720b631876db39b8ef04-kubeadm-1.6.0-0.alpha.0.2074.a092d8e0f95f52.x86_64.rpm

# Lock the version of these packages so that we don't upgrade them accidentally.
sudo yum versionlock add kubectl kubelet kubernetes-cni kubeadm

# Enable and start up docker and the kubelet
systemctl enable docker && systemctl start docker
systemctl enable kubelet && systemctl start kubelet

Running kubeadm init

Finally, when running kubeadm init you must specify the --use-kubernetes-version flag:

kubeadm init --use-kubernetes-version=v1.5.6

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