October 5th, 2016
緣起
2016/09/26 Google 推出了新版的 Kubernetes 1.4 裡頭最讓人期待的，就是 kubeadm 這個新的功能．
本來很期待他能夠讓 Kubernetes 變得更容易安裝並且加入新的節點，所以就試玩了一下．發現功能都還蠻強大的．不僅僅是變得更容易安裝，其實根本就是跟 docker swarm mode 致敬啊．整個變得簡單到不行．
建立機器
這邊只建議兩個 OS 版本:
- Ubuntu 16.04
- CentOS 7
備註: 如果你使用 docker-machine 來建立 VM 獲釋 GCP 上面的機器，預設的 Ubuntu 是 15.10 ，是無法順利安裝完畢的．
下載相關的 binary
每一台電腦（包括 Master 跟 Node 都得執行）所有的指令都是透過 sudo su -
# curl 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
# apt-get install -y docker.io kubelet kubeadm kubectl kubernetes-cni
啟動 Master
就像是 docker swarm mode 的 master 一樣，只要一行指令就好．
kubeadm init
詳細會出現的螢幕如下
# kubeadm init
<master/tokens> generated token: "306d01.da88f33b20103873"
<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 51.538064 seconds
<master/apiclient> waiting for at least one node to register and become ready
<master/apiclient> first node is ready after 0.504944 seconds
<master/discovery> created essential addon: kube-discovery, waiting for it to become ready
<master/discovery> kube-discovery is ready after 13.506671 seconds
<master/addons> created essential addon: kube-proxy
<master/addons> created essential addon: kube-dns
Kubernetes master initialised successfully!
You can now join any number of machines by running the following on each node:
kubeadm join --token 306d01.da88f33b20103873 10.240.0.11
備註: 當出現 waiting for at least one node to register and become ready 需要大概幾十秒鐘（取決你機器的速度）．
其他機器只要透過 kubeadm join --token 306d01.da88f33b20103873 10.240.0.11 就可以了．
Node 加入該群集 (Clustering)
kubeadm join --token 306d01.da88f33b20103873 10.240.0.11
詳細指令顯示如下：
# kubeadm join --token 306d01.da88f33b20103873 10.240.0.11
<util/tokens> validating provided token
<node/discovery> created cluster info discovery client, requesting info from "http://10.240.0.11:9898/cluster-info/v1/?token-id=306d01"
<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://10.240.0.11:443]
<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.
驗證 Kubernetes 叢集有成功建立
# kubectl get nodes
NAME STATUS AGE
evan-kube-1 Ready 1m
evan-kube-2 Ready 1m
evan-kube-master Ready 4m
建立 Clustering 的 network
# kubectl apply -f https://git.io/weave-kube
daemonset "weave-net" created
跑一些簡單的範例吧
透過 Console 直接建立兩個 Pods ，以下指令需要在 Master 輸入．
# kubectl get nodes
NAME STATUS AGE
evan-kube-1 Ready 1m
evan-kube-2 Ready 1m
evan-kube-master Ready 4m
root@evan-kube-master:~# cat <<EOF | kubectl create -f -
> apiVersion: v1
> kind: Pod
> metadata:
> name: busybox-sleep
> spec:
> containers:
> - name: busybox
> image: busybox
> args:
> - sleep
> - "1000000"
> ---
> apiVersion: v1
> kind: Pod
> metadata:
> name: busybox-sleep-less
> spec:
> containers:
> - name: busybox
> image: busybox
> args:
> - sleep
> - "1000"
> EOF
pod "busybox-sleep" created
pod "busybox-sleep-less" created
確認一下 Pod 有建立成功
# kubectl get pods
NAME READY STATUS RESTARTS AGE
busybox-sleep 1/1 Running 0 6s
busybox-sleep-less 1/1 Running 0 6s
確認一下每個 Pod 在哪個節點執行 ?
# kubectl describe pod busybox-sleep
Name: busybox-sleep
Namespace: default
Node: evan-kube-2/10.240.0.14
...
這樣就可以知道 pod busybox-sleep 在 evan-kube-2 這台機器．
再來確認另外一個 pod busybox-sleep-less 在哪個節點執行 ?
# kubectl describe pod busybox-sleep-less
Name: busybox-sleep-less
Namespace: default
Node: evan-kube-1/10.240.0.13
這樣就可以知道 pod busybox-sleep-less 在 evan-kube-1 這台機器．
限制 (Limitations)
- 目前
kubeadm還不支援 cloud-provider integrations, 所以如果需要 Load Balancers (LBs) 或是 Persistent Volumes (PVs) ．還是建議使用 GKE - 這樣建立的叢集只有一個 Master ，並且上面的 etcd 只有一個，如果需要備援或是要做 HA 就建議透過 etcd clustering 來做．
- 目前
kubectl logs還不支援kubeadm建立出的叢集，請看 issue 22770.
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