Kubernetesの基本を学ぶ

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Minikubを使用してローカル環境でKubernetesを動かす

Minikube is a tool that makes it easy to run Kubernetes locally. Minikube runs a single-node Kubernetes cluster inside a VM on your laptop for users looking to try out Kubernetes or develop with it day-to-day.

Minikubeの機能

インストール

See Installing Minikube.

クイックスタート

Here’s a brief demo of Minikube usage. If you want to change the VM driver add the appropriate --vm-driver=xxx flag to minikube start. Minikube supports the following drivers:

Note that the IP below is dynamic and can change. It can be retrieved with minikube ip.

$ minikube start
Starting local Kubernetes cluster...
Running pre-create checks...
Creating machine...
Starting local Kubernetes cluster...

$ kubectl run hello-minikube --image=k8s.gcr.io/echoserver:1.10 --port=8080
deployment.apps/hello-minikube created
$ kubectl expose deployment hello-minikube --type=NodePort
service/hello-minikube exposed

# We have now launched an echoserver pod but we have to wait until the pod is up before curling/accessing it
# via the exposed service.
# To check whether the pod is up and running we can use the following:
$ kubectl get pod
NAME                              READY     STATUS              RESTARTS   AGE
hello-minikube-3383150820-vctvh   0/1       ContainerCreating   0          3s
# We can see that the pod is still being created from the ContainerCreating status
$ kubectl get pod
NAME                              READY     STATUS    RESTARTS   AGE
hello-minikube-3383150820-vctvh   1/1       Running   0          13s
# We can see that the pod is now Running and we will now be able to curl it:
$ curl $(minikube service hello-minikube --url)


Hostname: hello-minikube-7c77b68cff-8wdzq

Pod Information:
	-no pod information available-

Server values:
	server_version=nginx: 1.13.3 - lua: 10008

Request Information:
	client_address=172.17.0.1
	method=GET
	real path=/
	query=
	request_version=1.1
	request_scheme=http
	request_uri=http://192.168.99.100:8080/

Request Headers:
	accept=*/*
	host=192.168.99.100:30674
	user-agent=curl/7.47.0

Request Body:
	-no body in request-


$ kubectl delete services hello-minikube
service "hello-minikube" deleted
$ kubectl delete deployment hello-minikube
deployment.extensions "hello-minikube" deleted
$ minikube stop
Stopping local Kubernetes cluster...
Stopping "minikube"...

コンテナランタイムの代替

containerd

To use containerd as the container runtime, run:

$ minikube start \
    --network-plugin=cni \
    --container-runtime=containerd \
    --bootstrapper=kubeadm

Or you can use the extended version:

$ minikube start \
    --network-plugin=cni \
    --extra-config=kubelet.container-runtime=remote \
    --extra-config=kubelet.container-runtime-endpoint=unix:///run/containerd/containerd.sock \
    --extra-config=kubelet.image-service-endpoint=unix:///run/containerd/containerd.sock \
    --bootstrapper=kubeadm

CRI-O

To use CRI-O as the container runtime, run:

$ minikube start \
    --network-plugin=cni \
    --container-runtime=cri-o \
    --bootstrapper=kubeadm

Or you can use the extended version:

$ minikube start \
    --network-plugin=cni \
    --extra-config=kubelet.container-runtime=remote \
    --extra-config=kubelet.container-runtime-endpoint=/var/run/crio.sock \
    --extra-config=kubelet.image-service-endpoint=/var/run/crio.sock \
    --bootstrapper=kubeadm

rktコンテナエンジン

To use rkt as the container runtime run:

$ minikube start \
    --network-plugin=cni \
    --container-runtime=rkt

This will use an alternative minikube ISO image containing both rkt, and Docker, and enable CNI networking.

ドライバープラグイン

See DRIVERS for details on supported drivers and how to install plugins, if required.

Dockerデーモンの再利用によるローカルイメージの使用

When using a single VM of Kubernetes, it’s really handy to reuse the Minikube’s built-in Docker daemon; as this means you don’t have to build a docker registry on your host machine and push the image into it - you can just build inside the same docker daemon as minikube which speeds up local experiments. Just make sure you tag your Docker image with something other than ‘latest’ and use that tag while you pull the image. Otherwise, if you do not specify version of your image, it will be assumed as :latest, with pull image policy of Always correspondingly, which may eventually result in ErrImagePull as you may not have any versions of your Docker image out there in the default docker registry (usually DockerHub) yet.

To be able to work with the docker daemon on your mac/linux host use the docker-env command in your shell:

eval $(minikube docker-env)

You should now be able to use docker on the command line on your host mac/linux machine talking to the docker daemon inside the minikube VM:

docker ps

On Centos 7, docker may report the following error:

Could not read CA certificate "/etc/docker/ca.pem": open /etc/docker/ca.pem: no such file or directory

The fix is to update /etc/sysconfig/docker to ensure that Minikube’s environment changes are respected:

< DOCKER_CERT_PATH=/etc/docker
---
> if [ -z "${DOCKER_CERT_PATH}" ]; then
>   DOCKER_CERT_PATH=/etc/docker
> fi

Remember to turn off the imagePullPolicy:Always, otherwise Kubernetes won’t use images you built locally.

クラスターの管理

クラスターの起動

The minikube start command can be used to start your cluster. This command creates and configures a Virtual Machine that runs a single-node Kubernetes cluster. This command also configures your kubectl installation to communicate with this cluster.

If you are behind a web proxy, you will need to pass this information to the minikube start command:

https_proxy=<my proxy> minikube start --docker-env http_proxy=<my proxy> --docker-env https_proxy=<my proxy> --docker-env no_proxy=192.168.99.0/24

Unfortunately just setting the environment variables will not work.

Minikube will also create a “minikube” context, and set it to default in kubectl. To switch back to this context later, run this command: kubectl config use-context minikube.

Kubernetesバージョンの指定

You can specify the specific version of Kubernetes for Minikube to use by adding the --kubernetes-version string to the minikube start command. For example, to run version v1.7.3, you would run the following:

minikube start --kubernetes-version v1.7.3

Kubernetesの設定

Minikube has a “configurator” feature that allows users to configure the Kubernetes components with arbitrary values. To use this feature, you can use the --extra-config flag on the minikube start command.

This flag is repeated, so you can pass it several times with several different values to set multiple options.

This flag takes a string of the form component.key=value, where component is one of the strings from the below list, key is a value on the configuration struct and value is the value to set.

Valid keys can be found by examining the documentation for the Kubernetes componentconfigs for each component. Here is the documentation for each supported configuration:

例

To change the MaxPods setting to 5 on the Kubelet, pass this flag: --extra-config=kubelet.MaxPods=5.

This feature also supports nested structs. To change the LeaderElection.LeaderElect setting to true on the scheduler, pass this flag: --extra-config=scheduler.LeaderElection.LeaderElect=true.

To set the AuthorizationMode on the apiserver to RBAC, you can use: --extra-config=apiserver.authorization-mode=RBAC.

クラスターの停止

The minikube stop command can be used to stop your cluster. This command shuts down the Minikube Virtual Machine, but preserves all cluster state and data. Starting the cluster again will restore it to it’s previous state.

クラスターの削除

The minikube delete command can be used to delete your cluster. This command shuts down and deletes the Minikube Virtual Machine. No data or state is preserved.

クラスターに触れてみよう

Kubectl

The minikube start command creates a kubectl context called “minikube”. This context contains the configuration to communicate with your Minikube cluster.

Minikube sets this context to default automatically, but if you need to switch back to it in the future, run:

kubectl config use-context minikube,

Or pass the context on each command like this: kubectl get pods --context=minikube.

ダッシュボード

To access the Kubernetes Dashboard, run this command in a shell after starting Minikube to get the address:

minikube dashboard

サービス

To access a service exposed via a node port, run this command in a shell after starting Minikube to get the address:

minikube service [-n NAMESPACE] [--url] NAME

ネットワーク

The Minikube VM is exposed to the host system via a host-only IP address, that can be obtained with the minikube ip command. Any services of type NodePort can be accessed over that IP address, on the NodePort.

To determine the NodePort for your service, you can use a kubectl command like this:

kubectl get service $SERVICE --output='jsonpath="{.spec.ports[0].nodePort}"'

永続化ボリューム

Minikube supports PersistentVolumes of type hostPath. These PersistentVolumes are mapped to a directory inside the Minikube VM.

The Minikube VM boots into a tmpfs, so most directories will not be persisted across reboots (minikube stop). However, Minikube is configured to persist files stored under the following host directories:

Here is an example PersistentVolume config to persist data in the /data directory:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001
spec:
  accessModes:
    - ReadWriteOnce
  capacity:
    storage: 5Gi
  hostPath:
    path: /data/pv0001/

ホストフォルダーのマウント

Some drivers will mount a host folder within the VM so that you can easily share files between the VM and host. These are not configurable at the moment and different for the driver and OS you are using.

Note: Host folder sharing is not implemented in the KVM driver yet.
Driver OS HostFolder VM
VirtualBox Linux /home /hosthome
VirtualBox macOS /Users /Users
VirtualBox Windows C://Users /c/Users
VMware Fusion macOS /Users /Users
Xhyve macOS /Users /Users

プライベートコンテナレジストリ

To access a private container registry, follow the steps on this page.

We recommend you use ImagePullSecrets, but if you would like to configure access on the Minikube VM you can place the .dockercfg in the /home/docker directory or the config.json in the /home/docker/.docker directory.

アドオン

In order to have Minikube properly start or restart custom addons, place the addons you wish to be launched with Minikube in the ~/.minikube/addons directory. Addons in this folder will be moved to the Minikube VM and launched each time Minikube is started or restarted.

HTTPプロキシ経由のMinikube利用

Minikube creates a Virtual Machine that includes Kubernetes and a Docker daemon. When Kubernetes attempts to schedule containers using Docker, the Docker daemon may require external network access to pull containers.

If you are behind an HTTP proxy, you may need to supply Docker with the proxy settings. To do this, pass the required environment variables as flags during minikube start.

For example:

$ minikube start --docker-env http_proxy=http://$YOURPROXY:PORT \
                 --docker-env https_proxy=https://$YOURPROXY:PORT

If your Virtual Machine address is 192.168.99.100, then chances are your proxy settings will prevent kubectl from directly reaching it. To by-pass proxy configuration for this IP address, you should modify your no_proxy settings. You can do so with:

$ export no_proxy=$no_proxy,$(minikube ip)

既知の問題

設計

Minikube uses libmachine for provisioning VMs, and kubeadm to provision a Kubernetes cluster.

For more information about Minikube, see the proposal.

追加リンク集

コミュニティ

Contributions, questions, and comments are all welcomed and encouraged! Minikube developers hang out on Slack in the #minikube channel (get an invitation here). We also have the kubernetes-dev Google Groups mailing list. If you are posting to the list please prefix your subject with “minikube: “.

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