CKA考试知识总结-1

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阅读时长 ≈ 20 mins.

这是一篇很长很长的文章，是去年CKA考试刚开始推出来的时候，我参与考试复习做过的一些知识点。基于做过的题，大概列出了具体的知识点，当时考试的时候还在使用v1.7版本，现在应该都要到v1.12了。

补充：这周收到CNCF的邮件，说是之前认证两年到期的CKA证书又延长了一年了（感叹：这是为了诱惑大家都来考证吗^_^）。

CKA证书

随着k8s声名大噪，国内一大堆公司推各种高价的包过培训班；我只想说：CNCF还真有些缺乏社区精神，更多的还是商业模式。但是，只要能够推动整个云原生的发展，随它吧~

为了让本文显得有说服力，我也把证书贴出来炫炫（认证ID末尾是0100，照理说刚好是第100位通过考试的），勿拍砖！

复习资料

废话不多讲，现在进入主题。

Job

Q: Create a Job that run 60 time with 2 jobs running in parallel

参考资料：https://kubernetes.io/docs/concepts/workloads/controllers/jobs-run-to-completion/

yaml

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apiVersion: batch/v1
kind: Job
metadata:
    name: pi
spec:
    completions: 10
    parallelism: 2
    activeDeadlineSeconds: 2
    template:
    metadata:
        name: pi
    spec:
        containers:
        - name: pi
        image: perl
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
        restartPolicy: Never

并行job

Job类型 使用示例 行为 completions Parallelism 备注
一次性Job 数据库迁移 创建一个Pod直至其成功结束 1 1
固定结束次数的Job 处理工作队列的Pod 依次创建一个Pod运行直至completions个成功结束 2+ 1
固定结束次数的并行Job 多个Pod同时处理工作队列 依次创建多个Pod运行直至completions个成功结束 2+ 2+
并行Job 多个Pod同时处理工作队列 创建一个或多个Pod直至有一个成功结束 1 2+ 不会创建多个，直接创建出一个

  • kubectl scale job
    A job can be scaled up using the kubectl scale command. For example, the following command sets .spec.parallelism of a job called myjob to 10:

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    $ kubectl scale  --replicas=10 jobs/myjob
    job "myjob" scaled

  • 注意

    1. parallelism: 表示并行执行的数量；
    2. completions：表示成功运行多少次就结束job；
    3. RestartPolicy仅支持Never或OnFailure；
    4. activeDeadlineSeconds标志失败Pod的重试最大时间，超过这个时间不会继续重试；
    5. kubectl scale其实是修改了job的parallelism属性，并不会对completetions产生影响。

Cronjob

cron 表达式格式:
cron

如果某一位为*/5 就表示每隔5x； 比如在min位的话，代表每隔5分钟

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root@test-9:~# kubectl run cronjob --schedule="*/1 * * * *" --restart=OnFailure --image=busybox -- /bin/sh -c "sleep 99"
cronjob "cronjob" created
root@test-9:~#
root@test-9:~# kubectl get cronjob
NAME      SCHEDULE      SUSPEND   ACTIVE    LAST SCHEDULE   AGE
cronjob   */1 * * * *   False     0         <none>
root@test-9:~#
root@test-9:~# kubectl get job
NAME                 DESIRED   SUCCESSFUL   AGE
cronjob-1510581480   1         0            1m
cronjob-1510581540   1         0            14s
root@test-9:~#
root@test-9:~# kubectl get pod
NAME                       READY     STATUS    RESTARTS   AGE
cronjob-1510581480-r49rq   1/1       Running   0          1m
cronjob-1510581540-tl4hn   1/1       Running   0          16s

kubectl top

Q: Find which Pod is taking max CPU
Use kubectl top to find CPU usage per pod

kubectl top node

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root@test-9:~/henry# kubectl top nodes
NAME      CPU(cores)   CPU%      MEMORY(bytes)   MEMORY%
test-10   41m          1%        2230Mi          14%
test-9    104m         2%        4931Mi          31%
root@test-9:~/henry#
root@test-9:~/henry#
root@test-9:~/henry# kubectl top nodes | awk '{print $1 "\t" $3|"sort -r -n"}'
test-9        2%
test-10        1%
NAME        CPU%

sort的参数：-r 表示反序排列； -n 表示按照数字排序
awk print的时候，使用”\t” 来区分两个列，同时，使用管道来排序

输出排序

Q: List all PersistentVolumes sorted by their name
Use kubectl get pv --sort-by= <- this problem is buggy & also by default kubectl give the output sorted by name.

排序

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root@test-9:~/henry# kcs get svc --sort-by=.metadata.uid
NAME                   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)         AGE
tiller-deploy          ClusterIP   10.43.155.15    <none>        44134/TCP       2h
monitoring-influxdb    ClusterIP   10.43.227.43    <none>        8086/TCP        2h
monitoring-grafana     ClusterIP   10.43.217.185   <none>        80/TCP          2h
kube-dns               ClusterIP   10.43.0.10      <none>        53/UDP,53/TCP   2h
kubernetes-dashboard   ClusterIP   10.43.36.245    <none>        9090/TCP        2h
heapster               ClusterIP   10.43.250.217   <none>        80/TCP          2h
root@test-9:~/henry#
root@test-9:~/henry# kcs get svc --sort-by=.metadata.name
NAME                   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)         AGE
heapster               ClusterIP   10.43.250.217   <none>        80/TCP          2h
kube-dns               ClusterIP   10.43.0.10      <none>        53/UDP,53/TCP   2h
kubernetes-dashboard   ClusterIP   10.43.36.245    <none>        9090/TCP        2h
monitoring-grafana     ClusterIP   10.43.217.185   <none>        80/TCP          2h
monitoring-influxdb    ClusterIP   10.43.227.43    <none>        8086/TCP        2h
tiller-deploy          ClusterIP   10.43.155.15    <none>        44134/TCP       2h

root@test-9:~/henry# kcs get svc heapster -o json
{
    "apiVersion": "v1",
    "kind": "Service",
    "metadata": {
        "creationTimestamp": "2017-11-12T03:27:51Z",
        "labels": {
            "kubernetes.io/cluster-service": "true",
            "kubernetes.io/name": "Heapster",
            "task": "monitoring"
        },
        "name": "heapster",
        "namespace": "kube-system",
        "resourceVersion": "229",
        "selfLink": "/api/v1/namespaces/kube-system/services/heapster",
        "uid": "769529c5-c759-11e7-8dee-02cdc7a8bd69"
    },
    "spec": {
        "clusterIP": "10.43.250.217",
        "ports": [
            {
                "port": 80,
                "protocol": "TCP",
                "targetPort": 8082
            }
        ],
        "selector": {
            "k8s-app": "heapster"
        },
        "sessionAffinity": "None",
        "type": "ClusterIP"
    },
    "status": {
        "loadBalancer": {}
    }
}

查询资源

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# Get commands with basic output
$ kubectl get services                          # List all services in the namespace
$ kubectl get pods --all-namespaces             # List all pods in all namespaces
$ kubectl get pods -o wide                      # List all pods in the namespace, with more details
$ kubectl get deployment my-dep                 # List a particular deployment
$ kubectl get pods --include-uninitialized      # List all pods in the namespace, including uninitialized ones

# Describe commands with verbose output
$ kubectl describe nodes my-node
$ kubectl describe pods my-pod

$ kubectl get services --sort-by=.metadata.name # List Services Sorted by Name

# List pods Sorted by Restart Count
$ kubectl get pods --sort-by='.status.containerStatuses[0].restartCount'

# Get the version label of all pods with label app=cassandra
$ kubectl get pods --selector=app=cassandra rc -o \
    jsonpath='{.items[*].metadata.labels.version}'

# Get ExternalIPs of all nodes
$ kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="ExternalIP")].address}'

# List Names of Pods that belong to Particular RC
# "jq" command useful for transformations that are too complex for jsonpath, it can be found at https://stedolan.github.io/jq/
$ sel=${$(kubectl get rc my-rc --output=json | jq -j '.spec.selector | to_entries | .[] | "\(.key)=\(.value),"')%?}
$ echo $(kubectl get pods --selector=$sel --output=jsonpath={.items..metadata.name})

# Check which nodes are ready
$ JSONPATH='{range .items[*]}{@.metadata.name}:{range @.status.conditions[*]}{@.type}={@.status};{end}{end}' \
    && kubectl get nodes -o jsonpath="$JSONPATH" | grep "Ready=True"

# List all Secrets currently in use by a pod
$ kubectl get pods -o json | jq '.items[].spec.containers[].env[]?.valueFrom.secretKeyRef.name' | grep -v null | sort | uniq

常用命令

kubectl run

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root@test-9:~# kubectl run demo-1 --image=busybox:latest --env="env1=wise2c" --port=80 --hostport=30098 --restart='Always' --image-pull-policy='Always' --limits="cpu=200m,memory=512Mi" --replicas=2 -- sleep 60
deployment "demo-1" created
root@test-9:~#
root@test-9:~# kubectl get pod
NAME                      READY     STATUS              RESTARTS   AGE
demo-1-4031462666-1m6lc   0/1       ContainerCreating   0          4s
demo-1-4031462666-3sph3   0/1       ContainerCreating   0          4s
root@test-9:~#
root@test-9:~# kubectl get deploy demo-1 -o yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
    annotations:
    deployment.kubernetes.io/revision: "1"
    creationTimestamp: 2017-11-12T06:20:52Z
    generation: 1
    labels:
    run: demo-1
    name: demo-1
    namespace: default
    resourceVersion: "13667"
    selfLink: /apis/extensions/v1beta1/namespaces/default/deployments/demo-1
    uid: a24a6b2b-c771-11e7-8dee-02cdc7a8bd69
spec:
    replicas: 2
    selector:
    matchLabels:
        run: demo-1
    strategy:
    rollingUpdate:
        maxSurge: 1
        maxUnavailable: 1
    type: RollingUpdate
    template:
    metadata:
        creationTimestamp: null
        labels:
        run: demo-1
    spec:
        containers:
        - args:
        - sleep
        - "60"
        env:
        - name: env1
            value: wise2c
        image: busybox:latest
        imagePullPolicy: Always
        name: demo-1
        ports:
        - containerPort: 80
            hostPort: 30098
            protocol: TCP
        resources:
            limits:
            cpu: 200m
            memory: 512Mi
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
        dnsPolicy: ClusterFirst
        restartPolicy: Always
        schedulerName: default-scheduler
        securityContext: {}
        terminationGracePeriodSeconds: 30
status:
    availableReplicas: 2
    conditions:
    - lastTransitionTime: 2017-11-12T06:22:03Z
    lastUpdateTime: 2017-11-12T06:22:03Z
    message: Deployment has minimum availability.
    reason: MinimumReplicasAvailable
    status: "True"
    type: Available
    observedGeneration: 1
    readyReplicas: 2
    replicas: 2
    updatedReplicas: 2

kubectl expose

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root@test-9:~# kubectl expose deploy nginx2 --name=nginx --port=80 --target-port=80 --protocol=TCP --type=ClusterIP
service "nginx" exposed
root@test-9:~# kubectl get svc nginx -o yaml
apiVersion: v1
kind: Service
metadata:
    creationTimestamp: 2017-11-12T07:32:48Z
    labels:
    run: nginx2
    name: nginx
    namespace: default
    resourceVersion: "20097"
    selfLink: /api/v1/namespaces/default/services/nginx
    uid: ae7774d4-c77b-11e7-8dee-02cdc7a8bd69
spec:
    clusterIP: 10.43.221.216
    ports:
    - port: 80
    protocol: TCP
    targetPort: 80
    selector:
    run: nginx2
    sessionAffinity: None
    type: ClusterIP
status:
    loadBalancer: {}  
root@test-9:~#
root@test-9:~#
root@test-9:~#
root@test-9:~#
root@test-9:~# kubectl expose deploy nginx2 --name=nginx --port=80 --target-port=80 --protocol=TCP --type=NodePort
service "nginx" exposed
root@test-9:~# kubectl get svc nginx -o yaml
apiVersion: v1
kind: Service
metadata:
    creationTimestamp: 2017-11-12T07:35:21Z
    labels:
    run: nginx2
    name: nginx
    namespace: default
    resourceVersion: "20296"
    selfLink: /api/v1/namespaces/default/services/nginx
    uid: 0a19d690-c77c-11e7-8dee-02cdc7a8bd69
spec:
    clusterIP: 10.43.120.19
    externalTrafficPolicy: Cluster
    ports:
    - nodePort: 30014
    port: 80
    protocol: TCP
    targetPort: 80
    selector:
    run: nginx2
    sessionAffinity: None
    type: NodePort
status:
    loadBalancer: {}

port-forward

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root@test-9:~# kubectl get pod -o wide
NAME                    READY     STATUS    RESTARTS   AGE       IP            NODE
nginx-f7d4dc847-bzlzq   1/1       Running   0          11h       10.244.0.24   test-9
nginx-f7d4dc847-lcq57   1/1       Running   0          11h       10.244.1.45   test-10
nginx-f7d4dc847-qs28j   1/1       Running   0          11h       10.244.0.25   test-9
nginx-f7d4dc847-s4xml   1/1       Running   0          11h       10.244.1.44   test-10
nginx-f7d4dc847-skb74   1/1       Running   0          11h       10.244.1.43   test-10
nginx-f7d4dc847-x9vh4   1/1       Running   0          11h       10.244.0.26   test-9
root@test-9:~# kubectl port-forward nginx-f7d4dc847-bzlzq 9090:80
Forwarding from 127.0.0.1:9090 -> 80
Handling connection for 9090
root@test-9:~#
root@test-9:~# curl 127.0.0.1:9090
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
...
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
root@test-9:~#

NetworkPolicy

Q: Create a NetworkPolicy to allow connect to port 8080 by busybox pod only
https://kubernetes.io/docs/concepts/workloads/controllers/jobs-run-to-completion/
Make sure to use apiVersion: extensions/v1beta1 which works on both 1.6 and 1.7

  • 在生效之前，必须先配置annotation来阻止所有的请求；
  • podSelector.matchLablesl：定义了该规则对哪些pod（destination）有效；
  • ingress：指定了允许带标签“access=true” 的pod访问这些服务；
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root@test-9:~# kubectl annotate ns default "net.beta.kubernetes.io/network-policy={\"ingress\": {\"isolation\": \"DefaultDeny\"}}"
namespace "default" annotated
root@test-9:~#
root@test-9:~#
root@test-9:~# kubectl describe ns default
Name:         default
Labels:       <none>
Annotations:  net.beta.kubernetes.io/network-policy={"ingress": {"isolation": "DefaultDeny"}}
Status:       Active
No resource quota.
No resource limits.
root@test-9:~#
root@test-9:~/henry# kubectl get pod --show-labels
NAME                      READY     STATUS    RESTARTS   AGE       LABELS
nginx2-2627548522-6f5kf   1/1       Running   0          22m       pod-template-hash=2627548522,run=nginx
nginx2-2627548522-8w87b   1/1       Running   0          22m       pod-template-hash=2627548522,run=nginx
root@test-9:~/henry# kubectl get svc nginx --show-labels
NAME      TYPE       CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE       LABELS
nginx     NodePort   10.43.120.19   <none>        80:30014/TCP   16m       run=nginx
root@test-9:~/henry# cat network-policy.yaml
kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
    name: access-nginx
spec:
    podSelector:
    matchLabels:
        run: nginx
    ingress:
    - from:
    - namespaceSelector:
        matchLabels:
            project: myproject
    - podSelector:
        matchLabels:
            access: "true"
    ports:
    - protocol: TCP
        port: 80
root@test-9:~/henry# kubectl get netpol
NAME           POD-SELECTOR   AGE
access-nginx   run=nginx      2m
root@test-9:~/henry# kubectl get netpol access-nginx -o yaml
apiVersion: extensions/v1beta1
kind: NetworkPolicy
metadata:
    creationTimestamp: 2017-11-12T07:40:38Z
    generation: 1
    name: access-nginx
    namespace: default
    resourceVersion: "20699"
    selfLink: /apis/extensions/v1beta1/namespaces/default/networkpolicies/access-nginx
    uid: c72191d1-c77c-11e7-8dee-02cdc7a8bd69
spec:
    ingress:
    - from:
    - podSelector:
        matchLabels:
            access: "true"
        ports:
        - port: 80
        protocol: TCP
    podSelector:
    matchLabels:
        run: nginx
root@test-9:~/henry#
root@test-9:~/henry# kubectl run busybox --rm -ti --labels="access=true" --image=busybox /bin/sh
If you don't see a command prompt, try pressing enter.
/ # wget nginx
Connecting to nginx (10.43.120.19:80)
index.html           100% |********************************************************************************************|   612   0:00:00 ETA
/ #

Node Broken

Q: fixing broken nodes, see
https://kubernetes.io/docs/concepts/architecture/nodes/

  • Node参数
    condition
    Address
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root@test-9:~# kubectl describe nodes
Name:               test-10
Roles:              <none>
Labels:             beta.kubernetes.io/arch=amd64
                    beta.kubernetes.io/instance-type=rancher
                    beta.kubernetes.io/os=linux
                    failure-domain.beta.kubernetes.io/region=Region1
                    failure-domain.beta.kubernetes.io/zone=FailureDomain1
                    io.rancher.host.docker_version=1.12
                    io.rancher.host.linux_kernel_version=4.4
                    kubernetes.io/hostname=test-10
Annotations:        io.rancher.labels.io.rancher.host.docker_version=
                    io.rancher.labels.io.rancher.host.linux_kernel_version=
                    node.alpha.kubernetes.io/ttl=0
                    volumes.kubernetes.io/controller-managed-attach-detach=true
Taints:             <none>
CreationTimestamp:  Sun, 12 Nov 2017 11:27:45 +0800
Conditions:
    Type             Status  LastHeartbeatTime                 LastTransitionTime                Reason                       Message
    ----             ------  -----------------                 ------------------                ------                       -------
    OutOfDisk        False   Sun, 12 Nov 2017 15:16:39 +0800   Sun, 12 Nov 2017 11:27:45 +0800   KubeletHasSufficientDisk     kubelet has sufficient disk space available
    MemoryPressure   False   Sun, 12 Nov 2017 15:16:39 +0800   Sun, 12 Nov 2017 11:27:45 +0800   KubeletHasSufficientMemory   kubelet has sufficient memory available
    DiskPressure     False   Sun, 12 Nov 2017 15:16:39 +0800   Sun, 12 Nov 2017 11:27:45 +0800   KubeletHasNoDiskPressure     kubelet has no disk pressure
    Ready            True    Sun, 12 Nov 2017 15:16:39 +0800   Sun, 12 Nov 2017 11:27:45 +0800   KubeletReady                 kubelet is posting ready status
Addresses:
    InternalIP:  10.144.102.117
    ExternalIP:  10.144.102.117
    Hostname:    test-10
Capacity:
    cpu:     4
    memory:  16301460Ki
    pods:    110
Allocatable:
    cpu:     4
    memory:  16199060Ki
    pods:    110
System Info:
    Machine ID:
    System UUID:                4ABB25CA-B353-450A-9787-28477ED72344
    Boot ID:                    689e31dc-e05d-48de-9068-e8460d15a9b6
    Kernel Version:             4.4.0-91-generic
    OS Image:                   Ubuntu 16.04.1 LTS
    Operating System:           linux
    Architecture:               amd64
    Container Runtime Version:  docker://1.12.6
    Kubelet Version:            v1.7.7-rancher1
    Kube-Proxy Version:         v1.7.7-rancher1
ExternalID:                  3cb02e3d-cb58-42c6-9a54-2fb5cfb836d2
Non-terminated Pods:         (4 in total)
    Namespace                  Name                                    CPU Requests  CPU Limits  Memory Requests  Memory Limits
    ---------                  ----                                    ------------  ----------  ---------------  -------------
    default                    demo-1-4031462666-1m6lc                 200m (5%)     200m (5%)   512Mi (3%)       512Mi (3%)
    default                    nginx-4217019353-k3mqk                  0 (0%)        0 (0%)      0 (0%)           0 (0%)
    kube-system                kube-dns-638003847-q28hb                260m (6%)     0 (0%)      110Mi (0%)       170Mi (1%)
    kube-system                kubernetes-dashboard-716739405-42t14    100m (2%)     100m (2%)   50Mi (0%)        50Mi (0%)
Allocated resources:
    (Total limits may be over 100 percent, i.e., overcommitted.)
    CPU Requests  CPU Limits  Memory Requests  Memory Limits
    ------------  ----------  ---------------  -------------
    560m (14%)    300m (7%)   672Mi (4%)       732Mi (4%)
Events:         <none>

Etcd

Q: etcd backup, see
https://kubernetes.io/docs/getting-started-guides/ubuntu/backups/
https://www.mirantis.com/blog/everything-you-ever-wanted-to-know-about-using-etcd-with-kubernetes-v1-6-but-were-afraid-to-ask/

  • Start Etcd

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    #start script:
    #========================================
    etcd --name 'default' \
    --data-dir '/root/data.etcd' \
    --ca-file '/pki/ca.crt' --cert-file '/pki/cert.crt' --key-file '/pki/key.key' \
    --peer-ca-file '/pki/ca.crt' --peer-cert-file '/pki/cert.crt' --peer-key-file '/pki/key.key' \
    --client-cert-auth \
    --peer-client-cert-auth \
    --listen-peer-urls https://localhost:2380 \
    --listen-client-urls https://localhost:2379 \
    --advertise-client-urls https://localhost:2379 \
    --initial-advertise-peer-urls https://localhost:2380 \
    --initial-cluster default=https://localhost:2380 \
    --initial-cluster-state 'new' \
    --initial-cluster-token 'etcd-cluster' \
    --debug


    #operate:
    #========================================
    etcdctl  --endpoint=https://localhost:2379 --ca-file=/pki/ca.crt --cert-file=/pki/cert.crt --key-file=/pki/key.key ls /

    如果要设置证书：

    1. 需要把访问的URL加上https
    2. 需要设置上图中红色部分的内容

  • Replacing a failed etcd member

    1. Get the member ID of the failed member1:

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      etcdctl --endpoints=http://10.0.0.2,http://10.0.0.3 member list

    2. The following message is displayed:

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      8211f1d0f64f3269, started, member1, http://10.0.0.1:12380, http://10.0.0.1:2379
      91bc3c398fb3c146, started, member2, http://10.0.0.1:2380, http://10.0.0.2:2379
      fd422379fda50e48, started, member3, http://10.0.0.1:2380, http://10.0.0.3:2379

    3. Remove the failed member:

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      etcdctl member remove 8211f1d0f64f3269

    4. The following message is displayed:

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      Removed member 8211f1d0f64f3269 from cluster

    5. Add the new member:

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      ./etcdctl member add member4 --peer-urls=http://10.0.0.4:2380

    6. The following message is displayed:

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      Member 2be1eb8f84b7f63e added to cluster ef37ad9dc622a7c4

    7. Start the newly added member on a machine with the IP 10.0.0.4:

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      bash export ETCD_NAME="member4" export ETCD_INITIAL_CLUSTER="member2=http://10.0.0.2:2380,member3=http://10.0.0.3:2380,member4=http://10.0.0.4:2380" export ETCD_INITIAL_CLUSTER_STATE=existing etcd [flags]

      需要知道，先从集群中添加，然后再启动对应的etcd member。
      另外，对于新启动的etcd member需要指定启动的状态为“existing”。

  • Backing up an etcd cluster

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    ETCDCTL_API=3 etcdctl --endpoints $ENDPOINT snapshot save snapshotdb
    # exit 0

    # verify the snapshot
    ETCDCTL_API=3 etcdctl --write-out=table snapshot status snapshotdb
    +----------+----------+------------+------------+
    |   HASH   | REVISION | TOTAL KEYS | TOTAL SIZE |
    +----------+----------+------------+------------+
    | fe01cf57 |       10 |          7 | 2.1 MB     |
    +----------+----------+------------+------------+

到此结束，别以为你已经学完了，后面还有呢。
看完这一篇，还有无数篇！My God~

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