Kubernetes

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Kuerbernetes (k8s) is an open source container cluster manager. Kubernetes' primary goal is to provide a platform for automating deployment, scaling, and operations of application containers across a luster of hosts. Kubernetes was released by Google on July 2015.

Design overview

Kubernetes is built through the definition of a set of components (building blocks or "primitives") which, when used collectively, provide a method for the deployment, maintenance, and scalability of container-based application clusters.

These "primitives" are designed to be loosely coupled (i.e., where little to no knowledge of the other component definitions is needed to use) as well as easily extensible through an API. Both the internal components of Kubernetes as well as the extensions and containers make use of this API.

Components

The building blocks of Kubernetes are the following:

Cluster 
A cluster is a set of machines (physical or virtual) on which your applications are managed and run. All machines are managed as a cluster (or set of clusters, depending on the topology used).
Nodes (minions) 
You can think of these as "container clients". These are the individual hosts (physical or virtual) that Docker is installed on and hosts the various containers within your managed cluster.
Each node will run etcd (a key-pair management and communication service, used by Kubernetes for exchanging messages and reporting on cluster status) as well as the Kubernetes Proxy.
Pods 
A pod consists of one or more containers. Those containers are guaranteed (by the cluster controller) to be located on the same host machine (aka "co-located") in order to facilitate sharing of resources. For an example, it makes sense to have database processes and data containers as close as possible. In fact, they really should be in the same pod.
Pods "work together", like in a multi-tiered application configuration. Each set of pods that define and implement a service (like MySQL or Apache) are defined by the label selector.
Pods are assigned unique IPs within each cluster. These allow an application to use ports without having to worry about conflicting port utilization.
Pods can contain definitions of disk volumes or shares, and then provide access from those to all the members (containers) within the pod.
Finally, pod management is done through the API or delegated to a controller.
Labels 
Clients can attach "key-value pairs" to any object in the system (like Pods or Nodes). These become the labels that identify them in the configuration and management of them. The key-value pairs can be used to filter, organize, and perform mass operations on a set of resources.
Selectors 
Label Selectors represent queries that are made against those labels. They resolve to the corresponding matching objects. A Selector expression matches labels to filter certain resources. For example, you may want to search for all pods that belong to a certain service, or find all containers that have a specific tier Label value as "database". Labels and Selectors are inherently two sides of the same coin. You can use Labels to classify resources and use Selectors to find them and use them for certain actions.
These two items are the primary way that grouping is done in Kubernetes and determine which components that a given operation applies to when indicated.
Controllers 
These are used in the management of your cluster. Controllers are the mechanism by which your desired configuration state is enforced.
Controllers manage a set of pods and, depending on the desired configuration state, may engage other controllers to handle replication and scaling (Replication Controller) of X number of containers and pods across the cluster. It is also responsible for replacing any container in a pod that fails (based on the desired state of the cluster).
Replication Controllers (RC) are a subset of Controllers and are an abstraction used to manage pod lifecycles. One of the key uses of RCs is to maintain a certain number of running Pods (e.g., for scaling or ensuring that at least one Pod is running at all times, etc.). It is considered a "best practice" to use RCs to define Pod lifecycles, rather than creating Pods directly.
Other controllers that can be engaged include a DaemonSet Controller (enforces a 1-to-1 ratio of pods to minions) and a Job Controller (that runs pods to "completion", such as in batch jobs).
Each set of pods any controller manages, is determined by the label selectors that are part of its definition.
Replica Sets
These define how many replicas of each Pod will be running. They also monitor and ensure the required number of Pods are running, replacing Pods that die. Replica Sets can act as replacements for Replication Controllers.
Services 
A Service is an abstraction on top of Pods, which provides a single IP address and DNS name by which the Pods can be accessed. This load balancing configuration is much easier to manage and helps scale Pods seamlessly.
Kubernetes can then provide service discovery and handle routing with the static IP for each pod as well as load balancing (round robin based) connections to that service among the pods that match the label selector indicated.
By default, although a service is only exposed inside a cluster, it can also be exposed outside a cluster, as needed.
Volumes 
A Volume is a directory with data, which is accessible to a container. The volume co-terminates with the Pods that encloses it.
Name 
A name by which a resource is identified.
Namespace 
A Namespace provides additional qualification to a resource name. This is especially helpful when multiple teams/projects are using the same cluster and there is a potential for name collision. You can think of a Namespace as a virtual wall between multiple clusters.
Annotations 
An Annotation is a Label, but with much larger data capacity. Typically, this data is not readable by humans and is not easy to filter through. Annotation is useful only for storing data that may not be searched, but is required by the resource (e.g., storing strong keys, etc.).
Control Pane
API

Component services

The component services running on a standard master/node(s) Kubernetes setup are as follows:

  • Kubernetes Master
    kube-apiserver 
    Exposes Kubernetes APIs
    kube-controller-manager 
    Runs controllers to handle nodes, endpoints, etc.
    kube-scheduler 
    Watches for new pods and assigns them nodes
    etcd 
    Distributed key-value store
    DNS 
    [optional] DNS for Kubernetes services
  • Nodes
    kubelet 
    Manages pods on node, volumes, secrets, creating new containers, health checks, etc.
    kube-proxy 
    Maintains network rules, port forwarding, etc.

Setup a Kubernetes cluster

In this section, I will show you how to setup a Kubernetes cluster with etcd and Docker. The cluster will consist of 1 master host and 3 minions (aka nodes).

Setup VMs

For this demo, I will be creating 4 VMs via Vagrant (with VirtualBox).

  • Create Vagrant demo environment:
$ mkdir $HOME/dev/kubernetes && cd $_
  • Create Vagrantfile with the following contents:
# -*- mode: ruby -*-
# vi: set ft=ruby :

require 'yaml'
VAGRANTFILE_API_VERSION = "2"

$common_script = <<COMMON_SCRIPT
# Set verbose
set -v
# Set exit on error
set -e
echo -e "$(date) [INFO] Starting modified Vagrant..."
sudo yum update -y
# Timestamp provision
date > /etc/vagrant_provisioned_at
COMMON_SCRIPT

unless defined? CONFIG
  configuration_file = File.join(File.dirname(__FILE__), 'vagrant_config.yml')
  CONFIG = YAML.load(File.open(configuration_file, File::RDONLY).read)
end

CONFIG['box'] = {} unless CONFIG.key?('box')

def modifyvm_network(node)
  node.vm.provider "virtualbox" do |vbox|
    vbox.customize ["modifyvm", :id, "--nicpromisc1", "allow-all"]
    #vbox.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
    vbox.customize ["modifyvm", :id, "--nicpromisc2", "allow-all"]
  end
end

def modifyvm_resources(node, memory, cpus)
  node.vm.provider "virtualbox" do |vbox|
    vbox.customize ["modifyvm", :id, "--memory", memory]
    vbox.customize ["modifyvm", :id, "--cpus", cpus]
  end
end

## START: Actual Vagrant process
Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|

  config.vm.box = CONFIG['box']['name']

  # Uncomment the following line if you wish to be able to pass files from
  # your local filesystem directly into the vagrant VM:
  #config.vm.synced_folder "data", "/vagrant"

## VM: k8s master #############################################################
  config.vm.define "master" do |node|
    node.vm.hostname = "k8s.master.dev"
    node.vm.provision "shell", inline: $common_script
    #node.vm.network "forwarded_port", guest: 80, host: 8080
    node.vm.network "private_network", ip: CONFIG['host_groups']['master']

    # Uncomment the following if you wish to define CPU/memory:
    #node.vm.provider "virtualbox" do |vbox|
    #  vbox.customize ["modifyvm", :id, "--memory", "4096"]
    #  vbox.customize ["modifyvm", :id, "--cpus", "2"]
    #end
    #modifyvm_resources(node, "4096", "2")
  end
## VM: k8s minion1 ############################################################
  config.vm.define "minion1" do |node|
    node.vm.hostname = "k8s.minion1.dev"
    node.vm.provision "shell", inline: $common_script
    node.vm.network "private_network", ip: CONFIG['host_groups']['minion1']
  end
## VM: k8s minion2 ############################################################
  config.vm.define "minion2" do |node|
    node.vm.hostname = "k8s.minion2.dev"
    node.vm.provision "shell", inline: $common_script
    node.vm.network "private_network", ip: CONFIG['host_groups']['minion2']
  end
## VM: k8s minion3 ############################################################
  config.vm.define "minion3" do |node|
    node.vm.hostname = "k8s.minion3.dev"
    node.vm.provision "shell", inline: $common_script
    node.vm.network "private_network", ip: CONFIG['host_groups']['minion3']
  end
###############################################################################

end

The above Vagrantfile uses the following configuration file:

$ cat vagrant_config.yml
---
box:
  name: centos/7
  storage_controller: 'SATA Controller'
debug: false
development: false
network:
  dns1: 8.8.8.8
  dns2: 8.8.4.4
  internal:
    network: 192.168.200.0/24
  external:
    start: 192.168.100.100
    end: 192.168.100.200
    network: 192.168.100.0/24
    bridge: wlan0
    netmask: 255.255.255.0
    broadcast: 192.168.100.255
host_groups:
  master: 192.168.200.100
  minion1: 192.168.200.101
  minion2: 192.168.200.102
  minion3: 192.168.200.103
  • In the Vagrant Kubernetes directory (i.e., $HOME/dev/kubernetes), run the following command:
$ vagrant up

Setup hosts

Note: Run the following commands/steps on all hosts (master and minions).

  • Log into the k8s master host:
$ vagrant ssh master
  • Kubernetes cluster
$ cat << EOF >> /etc/hosts
192.168.200.100    k8s.master.dev
192.168.200.101    k8s.minion1.dev
192.168.200.102    k8s.minion2.dev
192.168.200.103    k8s.minion3.dev
EOF
  • Install, enable, and start NTP:
$ yum install -y ntp
$ systemctl enable ntpd && systemctl start ntpd
$ timedatectl
  • Disable any firewall rules (for now; we will add the rules back later):
$ systemctl stop firewalld && systemctl disable firewalld
$ systemctl stop iptables
  • Disable SELinux (for now; we will turn it on again later):
$ setenforce 0
$ sed -i 's/^SELINUX=.*/SELINUX=permissive/' /etc/sysconfig/selinux
$ sed -i 's/^SELINUX=.*/SELINUX=permissive/' /etc/selinux/config
$ sestatus
  • Add the Docker repo and update yum:
$ cat << EOF > /etc/yum.repos.d/virt7-docker-common-release.repo
[virt7-docker-common-release]
name=virr7-docker-common-release
baseurl=http://cbs.centos.org/repos/virt7-docker-common-release/x86_64/os/
gpgcheck=0
EOF
$ yum update
  • Install Docker, Kubernetes, and etcd:
$ yum install -y --enablerepo=virt7-docker-common-release kubernetes docker etcd

Install and configure master controller

Note: Run the following commands on only the master host.

  • Edit /etc/kubernetes/config and add (or make changes to) the following lines:
KUBE_MASTER="--master=http://k8s.master.dev:8080"
KUBE_ETCD_SERVERS="--etcd-servers=http://k8s.master.dev:2379"
  • Edit /etc/etcd/etcd.conf and add (or make changes to) the following lines:
[member]
ETCD_LISTEN_CLIENT_URLS="http://0.0.0.0:2379"
[cluster]
ETCD_ADVERTISE_CLIENT_URLS="http://0.0.0.0:2379"
  • Edit /etc/kubernetes/apiserver and add (or make changes to) the following lines:
# The address on the local server to listen to.
#KUBE_API_ADDRESS="--insecure-bind-address=127.0.0.1"
KUBE_API_ADDRESS="--address=0.0.0.0"

# The port on the local server to listen on.
KUBE_API_PORT="--port=8080"

# Port minions listen on
KUBELET_PORT="--kubelet-port=10250"

# Comma separated list of nodes in the etcd cluster
KUBE_ETCD_SERVERS="--etcd-servers=http://127.0.0.1:2379"

# Address range to use for services
KUBE_SERVICE_ADDRESSES="--service-cluster-ip-range=10.254.0.0/16"

# default admission control policies
#KUBE_ADMISSION_CONTROL="--admission-control=NamespaceLifecycle,NamespaceExists,LimitRanger,SecurityContextDeny,ServiceAccount,ResourceQuota"

# Add your own!
KUBE_API_ARGS=""
  • Enable and start the following etcd and Kubernetes services:
$ for SERVICE in etcd kube-apiserver kube-controller-manager kube-scheduler; do
      systemctl restart $SERVICE
      systemctl enable $SERVICE
      systemctl status $SERVICE 
  done
  • Check on the status of the above services (the following command should report 4 running services):
$ systemctl status etcd kube-apiserver kube-controller-manager kube-scheduler | grep "(running)" | wc -l # => 4
  • Check on the status of the Kubernetes API server:
$ kubectl cluster-info
Kubernetes master is running at http://localhost:8080
$ curl http://localhost:8080/version
#~OR~
$ curl http://k8s.master.dev:8080/version
{
  "major": "1",
  "minor": "2",
  "gitVersion": "v1.2.0",
  "gitCommit": "ec7364b6e3b155e78086018aa644057edbe196e5",
  "gitTreeState": "clean"
}
  • Get a list of Kubernetes API paths:
$ curl http://k8s.master.dev:8080/paths
{
  "paths": [
    "/api",
    "/api/v1",
    "/apis",
    "/apis/autoscaling",
    "/apis/autoscaling/v1",
    "/apis/batch",
    "/apis/batch/v1",
    "/apis/extensions",
    "/apis/extensions/v1beta1",
    "/healthz",
    "/healthz/ping",
    "/logs/",
    "/metrics",
    "/resetMetrics",
    "/swagger-ui/",
    "/swaggerapi/",
    "/ui/",
    "/version"
  ]
}
  • List all available paths (key-value stores) known to ectd:
$ etcdctl ls / --recursive

The master controller in a Kubernetes cluster must have the following services running to function as the master host in the cluster:

  • ntpd
  • etcd
  • kube-controller-manager
  • kube-apiserver
  • kube-scheduler

Note: The Docker daemon should not be running on the master host.

Install and configure the minions

Note: Run the following commands/steps on all minion hosts.

  • Log into the k8s minion hosts:
$ vagrant ssh minion1  # do the same for minion2 and minion3
  • Edit /etc/kubernetes/config and add (or make changes to) the following lines:
KUBE_MASTER="--master=http://k8s.master.dev:8080"
KUBE_ECTD_SERVERS="--etcd-servers=http://k8s.master.dev:2379"
  • Edit /etc/kubernetes/kubelet and add (or make changes to) the following lines:
###
# kubernetes kubelet (minion) config

# The address for the info server to serve on (set to 0.0.0.0 or "" for all interfaces)
KUBELET_ADDRESS="--address=0.0.0.0"

# The port for the info server to serve on
KUBELET_PORT="--port=10250"

# You may leave this blank to use the actual hostname
KUBELET_HOSTNAME="--hostname-override=k8s.minion1.dev"  # ***CHANGE TO CORRECT MINION HOSTNAME***

# location of the api-server
KUBELET_API_SERVER="--api-servers=http://k8s.master.dev:8080"

# pod infrastructure container
#KUBELET_POD_INFRA_CONTAINER="--pod-infra-container-image=registry.access.redhat.com/rhel7/pod-infrastructure:latest"

# Add your own!
KUBELET_ARGS=""
  • Enable and start the following services:
$ for SERVICE in kube-proxy kubelet docker; do
      systemctl restart $SERVICE
      systemctl enable $SERVICE
      systemctl status $SERVICE
  done
  • Test that Docker is running and can start containers:
$ docker info
$ docker pull hello-world
$ docker run hello-world

Each minion in a Kubernetes cluster must have the following services running to function as a member of the cluster (i.e., a "Ready" node):

  • ntpd
  • kubelet
  • kube-proxy
  • docker

Kubectl: Exploring our environment

Note: Run all of the following commands on the master host.

  • Get a list of nodes with kubectl:
$ kubectl get nodes
NAME              STATUS    AGE
k8s.minion1.dev   Ready     20m
k8s.minion2.dev   Ready     12m
k8s.minion3.dev   Ready     12m
  • Describe nodes with kubectl:
$ kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="ExternalIP")].address}'
$ kubectl get nodes -o jsonpath='{range .items[*]}{@.metadata.name}:{range @.status.conditions[*]}{@.type}={@.status};{end}{end}' | tr ';' "\n"
k8s.minion1.dev:OutOfDisk=False
Ready=True
k8s.minion2.dev:OutOfDisk=False
Ready=True
k8s.minion3.dev:OutOfDisk=False
Ready=True
  • Get the man page for kubectl:
$ man kubectl-get

Working with our Kubernetes cluster

Note: The following section will be working from within the Kubernetes cluster we created above.

Create and deploy pod definitions

  • Turn off nodes 1 and 2:
minion{1,2}$ systemctl stop kubelet kube-proxy
master$ kubectl get nodes
NAME              STATUS     AGE
k8s.minion1.dev   Ready      1h
k8s.minion2.dev   NotReady   37m
k8s.minion3.dev   NotReady   39m
  • Check for any k8s Pods (there should be none):
master$ kubectl get pods
  • Create a builds directory for our Pods:
master$ mkdir builds && cd $_
  • Create a Pod running Nginx inside a Docker container:
master$ kubectl create -f - <<EOF
---
apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.7.9
    ports:
    - containerPort: 80
EOF
  • Check on Pod creation status:
master$ kubectl get pods
NAME      READY     STATUS              RESTARTS   AGE
nginx     0/1       ContainerCreating   0          2s
master$ kubectl get pods
NAME      READY     STATUS    RESTARTS   AGE
nginx     1/1       Running   0          3m
minion1$ docker ps
CONTAINER ID        IMAGE        COMMAND                 CREATED        STATUS        PORTS  NAMES
a718c6c0355d        nginx:1.7.9  "nginx -g 'daemon off"  3 minutes ago  Up 3 minutes         k8s_nginx.4580025_nginx_default_699e...
master$ kubectl describe pod nginx
master$ kubectl run busybox --image=busybox --restart=Never --tty -i --generator=run-pod/v1
busybox$ wget -qO- 172.17.0.2
master$ kubectl delete pod busybox
master$ kubectl delete pod nginx
  • Port forwarding:
master$ kubectl create -f nginx.yml  # see above for YAML
master$ kubectl port-forward nginx :80 &
I1020 23:12:29.478742   23394 portforward.go:213] Forwarding from [::1]:40065 -> 80
master$ curl -I localhost:40065

Tags, labels, and selectors

master$ cat << EOF > nginx-pod-label.yml
---
apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.7.9
    ports:
    - containerPort: 80
EOF
master$ kubectl create -f nginx-pod-label.yml
master$ kubectl get pods -l app=nginx
master$ kubectl describe pods -l app=nginx2
  • Add labels or overwrite existing ones:
master$ kubectl label pods nginx new-label=mynginx
master$ kubectl describe pods/nginx | awk '/^Labels/{print $2}'
new-label=nginx
master$ kubectl label pods nginx new-label=foo
master$ kubectl describe pods/nginx | awk '/^Labels/{print $2}'
new-label=foo

Deployments

master$ cat << EOF > nginx-deployment-dev.yml
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment-dev
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx-deployment-dev
    spec:
      containers:
      - name: nginx-deployment-dev
        image: nginx:1.7.9
        ports:
        - containerPort: 80
EOF
master$ cat nginx-deployment-prod.yml
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment-prod
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx-deployment-prod
    spec:
      containers:
      - name: nginx-deployment-prod
        image: nginx:1.7.9
        ports:
        - containerPort: 80
master$ kubectl create --validate -f nginx-deployment-dev.yml
master$ kubectl create --validate -f nginx-deployment-prod.yml
master$ kubectl get pods
NAME                                     READY     STATUS    RESTARTS   AGE
nginx-deployment-dev-104434401-jiiic     1/1       Running   0          5m
nginx-deployment-prod-3051195443-hj9b1   1/1       Running   0          12m
master$ kubectl describe deployments -l app=nginx-deployment-dev
Name:                   nginx-deployment-dev
Namespace:              default
CreationTimestamp:      Thu, 20 Oct 2016 23:48:46 +0000
Labels:                 app=nginx-deployment-dev
Selector:               app=nginx-deployment-dev
Replicas:               1 updated | 1 total | 1 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  1 max unavailable, 1 max surge
OldReplicaSets:         <none>
NewReplicaSet:          nginx-deployment-dev-2568522567 (1/1 replicas created)
...
master$ kubectl get deployments
NAME                    DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment-prod   1         1         1            1           44s
master$ cat << EOF > nginx-deployment-dev-update.yml
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment-dev
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx-deployment-dev
    spec:
      containers:
      - name: nginx-deployment-dev
        image: nginx:1.8  # ***CHANGED***
        ports:
        - containerPort: 80
master$ kubectl apply -f nginx-deployment-dev-update.yml
master$ kubectl get pods -l app=nginx-deployment-dev
NAME                                   READY     STATUS              RESTARTS   AGE
nginx-deployment-dev-104434401-jiiic   0/1       ContainerCreating   0          27s
master$ kubectl get pods -l app=nginx-deployment-dev
NAME                                   READY     STATUS    RESTARTS   AGE
nginx-deployment-dev-104434401-jiiic   1/1       Running   0          6m
  • Cleanup:
master$ kubectl delete deployment nginx-deployment-dev
master$ kubectl delete deployment nginx-deployment-prod

Multi-Pod (container) replication controller

  • Start the other two nodes (the ones we previously stopped):
minion2$ systemctl start kubelet kube-proxy
minion3$ systemctl start kubelet kube-proxy
master$ kubectl get nodes
NAME              STATUS    AGE
k8s.minion1.dev   Ready     2h
k8s.minion2.dev   Ready     2h
k8s.minion3.dev   Ready     2h
master$ cat << EOF > nginx-multi-node.yml
---
apiVersion: v1
kind: ReplicationController
metadata:
  name: nginx-www
spec:
  replicas: 3
  selector:
    app: nginx
  template:
    metadata:
      name: nginx
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
master$ kubectl create -f nginx-multi-node.yml
master$ kubectl get pods
NAME              READY     STATUS              RESTARTS   AGE
nginx-www-2evxu   0/1       ContainerCreating   0          10s
nginx-www-416ct   0/1       ContainerCreating   0          10s
nginx-www-ax41w   0/1       ContainerCreating   0          10s
master$ kubectl get pods
NAME              READY     STATUS    RESTARTS   AGE
nginx-www-2evxu   1/1       Running   0          1m
nginx-www-416ct   1/1       Running   0          1m
nginx-www-ax41w   1/1       Running   0          1m
master$ kubectl describe pods | awk '/^Node/{print $2}'
k8s.minion2.dev/192.168.200.102
k8s.minion1.dev/192.168.200.101
k8s.minion3.dev/192.168.200.103
minion1$ docker ps # 1 nginx container running
minion2$ docker ps # 1 nginx container running
minion3$ docker ps # 1 nginx container running
minion3$ docker ps --format "{{.Image}}"
nginx
gcr.io/google_containers/pause:2.0
master$ kubectl describe replicationcontroller
Name:       nginx-www
Namespace:  default
Image(s):   nginx
Selector:   app=nginx
Labels:     app=nginx
Replicas:   3 current / 3 desired
Pods Status:    3 Running / 0 Waiting / 0 Succeeded / 0 Failed
...
  • Attempt to delete one of the three pods:
master$ kubectl get pods
NAME              READY     STATUS    RESTARTS   AGE
nginx-www-2evxu   1/1       Running   0          11m
nginx-www-416ct   1/1       Running   0          11m
nginx-www-ax41w   1/1       Running   0          11m
master$ kubectl delete pod nginx-www-2evxu
master$ kubectl get pods
NAME              READY     STATUS    RESTARTS   AGE
nginx-www-3cck4   1/1       Running   0          12s
nginx-www-416ct   1/1       Running   0          11m
nginx-www-ax41w   1/1       Running   0          11m

A new pod (nginx-www-3cck4) automatically started up. This is because the expected state, as defined in our YAML file, is for there to be 3 pods running at all times. Thus, if one or more of the pods were to go down, a new pod (or pods) will automatically start up to bring the state back to the expected state.

  • To force-delete all pods:
master$ kubectl delete replicationcontroller nginx-www
master$ kubectl get pods  # nothing

Create and deploy service definitions

master$ cat << EOF > nginx-service.yml
---
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  ports:
  - port: 8000
    targetPort: 80
    protocol: TCP
  selector:
    app: nginx
EOF
master$ kubectl get services
NAME            CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
kubernetes      10.254.0.1       <none>        443/TCP    3h
master$ kubectl create -f nginx-service.yml
master$ kubectl get services
NAME            CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
kubernetes      10.254.0.1       <none>        443/TCP    3h
nginx-service   10.254.110.127   <none>        8000/TCP   10s
master$ kubectl run busybox --generator=run-pod/v1 --image=busybox --restart=Never --tty -i
busybox$ wget -qO- 10.254.110.127:8000  # works
  • Cleanup
master$ kubectl delete pod busybox
master$ kubectl delete service nginx-service
master$ kubectl get pods
NAME              READY     STATUS    RESTARTS   AGE
nginx-www-jh2e9   1/1       Running   0          13m
nginx-www-jir2g   1/1       Running   0          13m
nginx-www-w91uw   1/1       Running   0          13m
master$ kubectl delete replicationcontroller nginx-www
master$ kubectl get pods  # nothing

Creating temporary Pods at the CLI

  • Make sure we have no Pods running:
master$ kubectl get pods
  • Create temporary deployment pod:
master$ kubectl run mysample --image=foobar/apache
master$ kubectl get pods
NAME                        READY     STATUS              RESTARTS   AGE
mysample-1424711890-fhtxb   0/1       ContainerCreating   0          1s
master$ kubectl get deployment 
NAME       DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
mysample   1         1         1            0           7s
  • Create a temporary deployment pod (where we know it will fail):
master$ kubectl run myexample --image=christophchamp/ubuntu_sysadmin
master$ kubectl -o wide get pods
NAME                         READY     STATUS             RESTARTS   AGE       NODE
myexample-3534121234-mpr35   0/1       CrashLoopBackOff   12         39m       k8s.minion3.dev
mysample-2812764540-74c5h    1/1       Running            0          41m       k8s.minion2.dev
  • Check on why the "myexample" pod is in status "CrashLoopBackOff":
master$ kubectl describe pods/myexample-3534121234-mpr35
master$ kubectl describe deployments/mysample
master$ kubectl describe pods/mysample-2812764540-74c5h | awk '/^Node/{print $2}'
k8s.minion2.dev/192.168.200.102
master$ kubectl delete deployment mysample
  • Run multiple replicas of the same pod:
master$ kubectl run myreplicas --image=latest123/apache --replicas=2 --labels=app=myapache,version=1.0.0
master$ kubectl describe deployment myreplicas 
Name:           myreplicas
Namespace:      default
CreationTimestamp:  Fri, 21 Oct 2016 19:10:30 +0000
Labels:         app=myapache,version=1.0.0
Selector:       app=myapache,version=1.0.0
Replicas:       2 updated | 2 total | 1 available | 1 unavailable
StrategyType:       RollingUpdate
MinReadySeconds:    0
RollingUpdateStrategy:  1 max unavailable, 1 max surge
OldReplicaSets:     <none>
NewReplicaSet:      myreplicas-2209834598 (2/2 replicas created)
...
master$ kubectl get pods -o wide
NAME                          READY     STATUS             RESTARTS   AGE       NODE
myreplicas-2209834598-5iyer   1/1       Running            0          1m        k8s.minion1.dev
myreplicas-2209834598-cslst   1/1       Running            0          1m        k8s.minion2.dev
master$ kubectl describe pods -l version=1.0.0
  • Cleanup:
master$ kubectl delete deployment myreplicas

Interacting with Pod containers

  • Create example Apache pod definition file:
master$ cat << EOF > apache.yml
---
apiVersion: v1
kind: Pod
metadata:
  name: apache
spec:
  containers:
  - name: apache
    image: latest123/apache
    ports:
    - containerPort: 80
EOF
master$ kubectl create -f apache.yml
master$ kubectl get pods -o wide
NAME                          READY     STATUS    RESTARTS   AGE       NODE
apache                        1/1       Running   0          12m       k8s.minion3.dev
  • Test pod and make some basic configuration changes:
master$ kubectl exec apache date
master$ kubectl exec mypod -i -t -- cat /var/www/html/index.html  # default apache HTML
master$ kubectl exec apache -i -t -- /bin/bash
container$ export TERM=xterm
container$ echo "xtof test" > /var/www/html/index.html
minion3$ curl 172.17.0.2
xtof test
container$ exit
master$ kubectl get pods -o wide
NAME                          READY     STATUS    RESTARTS   AGE       NODE
apache                        1/1       Running   0          12m       k8s.minion3.dev

Pod/container is still running even after we exited (as expected).

  • Cleanup:
master$ kubectl delete pod apache

Logs

  • Start our example Apache pod to use for checking Kubernetes logging features:
master$ kubectl create -f apache.yml 
master$ kubectl get pods
NAME      READY     STATUS    RESTARTS   AGE
apache    1/1       Running   0          9s
master$ kubectl logs apache
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.2. Set the 'ServerName' directive globally to suppress this message
master$ kubectl logs --tail=10 apache
master$ kubectl logs --since=24h apache  # or 10s, 2m, etc.
master$ kubectl logs -f apache  # follow the logs
master$ kubectl logs -f -c apache apache  # where -c is the container ID
  • Cleanup:
master$ kubectl delete pod apache

Autoscaling and scaling Pods

master$ kubectl run myautoscale --image=latest123/apache --port=80 --labels=app=myautoscale
master$ kubectl get pods -o wide
NAME                           READY     STATUS    RESTARTS   AGE       NODE
myautoscale-3243017378-kq4z7   1/1       Running   0          47s       k8s.minion3.dev
  • Create an autoscale definition:
master$ kubectl autoscale deployment myautoscale --min=2 --max=6 --cpu-percent=80
master$ kubectl get deployments
NAME          DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
myautoscale   2         2         2            2           4m
master$ kubectl get pods -o wide
NAME                           READY     STATUS    RESTARTS   AGE       NODE
myautoscale-3243017378-kq4z7   1/1       Running   0          3m        k8s.minion3.dev
myautoscale-3243017378-r2f3d   1/1       Running   0          4s        k8s.minion2.dev
  • Scale up an already autoscaled deployment:
master$ kubectl scale --current-replicas=2 --replicas=4 deployment/myautoscale
master$ kubectl get deployments
NAME          DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
myautoscale   4         4         4            4           8m
master$ kubectl get pods -o wide
NAME                           READY     STATUS    RESTARTS   AGE       NODE
myautoscale-3243017378-2rxhp   1/1       Running   0          8s        k8s.minion1.dev
myautoscale-3243017378-kq4z7   1/1       Running   0          7m        k8s.minion3.dev
myautoscale-3243017378-ozxs8   1/1       Running   0          8s        k8s.minion3.dev
myautoscale-3243017378-r2f3d   1/1       Running   0          4m        k8s.minion2.dev
  • Scale down:
master$ kubectl scale --current-replicas=4 --replicas=2 deployment/myautoscale

Note: You can not scale down past the original minimum number of pods/containers specified in the original autoscale deployment (i.e., min=2 in our example).

  • Cleanup:
master$ kubectl delete deployment myautoscale

Failure and recovery

master$ kubectl run myrecovery --image=latest123/apache --port=80 --replicas=2 --labels=app=myrecovery
master$ kubectl get deployments
NAME         DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
myrecovery   2         2         2            2           6s
master$ kubectl get pods -o wide
NAME                         READY     STATUS    RESTARTS   AGE       NODE
myrecovery-563119102-5xu8f   1/1       Running   0          12s       k8s.minion1.dev
myrecovery-563119102-zw6wp   1/1       Running   0          12s       k8s.minion2.dev
  • Now stop Kubernetes- and Docker-related services on one of the minions/nodes (so we have a total of 2 nodes online):
minion1$ systemctl stop docker kubelet kube-proxy
master$ kubectl get pods -o wide
NAME                         READY     STATUS    RESTARTS   AGE       NODE
myrecovery-563119102-qyi04   1/1       Running   0          7m        k8s.minion3.dev
myrecovery-563119102-zw6wp   1/1       Running   0          14m       k8s.minion2.dev

Pod switch from minion1 to minion3.

  • Now stop Kubernetes- and Docker-related services on one of the remaining online minions/nodes (so we have a total of 1 node online):
minion2$ systemctl stop docker kubelet kube-proxy
master$ kubectl get pods -o wide
NAME                         READY     STATUS    RESTARTS   AGE       NODE
myrecovery-563119102-b5tim   1/1       Running   0          2m        k8s.minion3.dev
myrecovery-563119102-qyi04   1/1       Running   0          17m       k8s.minion3.dev

Both Pods are now running on minion3, the only available node.

  • Start up Kubernetes- and Docker-related services again on minion1 and delete on of the Pods:
minion1$ systemctl start docker kubelet kube-proxy
master$ kubectl delete pod myrecovery-563119102-b5tim
master$ kubectl get pods -o wide
NAME                         READY     STATUS    RESTARTS   AGE       NODE
myrecovery-563119102-8unzg   1/1       Running   0          1m        k8s.minion1.dev
myrecovery-563119102-qyi04   1/1       Running   0          20m       k8s.minion3.dev

Pods are now running on separate nodes.

  • Cleanup:
master$ kubectl delete deployments/myrecovery

External links