写在前面
kubernetes中涉及很多概念，包含云生态社区中各类技术，学习成本比较高，k8s中通常以编写yaml文件完成资源的部署，对于较多入门的人来说是个较高的门坎，本文以命令行的形式代理大家快速入门，俯瞰kubernetes核心概念，快速入门。
1. 基础概念
1.1 集群与节点
kubernetes是一个开源的容器引擎管理平台，实现容器化应用的自动化部署，任务调度，弹性伸缩，负载均衡等功能，cluster是由master和node两种角色组成，其中master负责管理集群，master节点由kube-apiserver，kube-controller-manager，kube-scheduler，etcd角色组成，node节点运行实际的应用，由Container Runtime，kubelet和kube-proxy组成，其中Container Runtime可能是Docker，rke，containerd，node节点可由物理机或者虚拟机组成。
1、查看master组件角色
[root@node-1 ~]# kubectl get componentstatuses
NAME STATUS MESSAGE ERROR
scheduler Healthy ok
controller-manager Healthy ok
etcd-0 Healthy {"health":"true"}
2、 查看node节点列表
[root@node-1 ~]# kubectl get nodes
NAME STATUS ROLES AGE VERSION
node-1 Ready master 26h v1.14.1
node-2 Ready <none> 26h v1.14.1
node-3 Ready <none> 26h v1.14.1
3、查看node节点详情
[root@node-1 ~]# kubectl describe node node-3
Name: node-3
Roles: <none>
Labels: beta.kubernetes.io/arch=amd64。#标签和Annotations
beta.kubernetes.io/os=linux
kubernetes.io/arch=amd64
kubernetes.io/hostname=node-3
kubernetes.io/os=linux
Annotations: flannel.alpha.coreos.com/backend-data: {"VtepMAC":"22:f8:75:bb:da:4e"}
flannel.alpha.coreos.com/backend-type: vxlan
flannel.alpha.coreos.com/kube-subnet-manager: true
flannel.alpha.coreos.com/public-ip: 10.254.100.103
kubeadm.alpha.kubernetes.io/cri-socket: /var/run/dockershim.sock
node.alpha.kubernetes.io/ttl: 0
volumes.kubernetes.io/controller-managed-attach-detach: true
CreationTimestamp: Sat, 10 Aug 2019 17:50:00 +0800
Taints: <none>
Unschedulable: false。#是否禁用调度，cordon命令控制的标识位。
Conditions: #资源调度能力，MemoryPressure内存是否有压力（即内存不足）
#DiskPressure磁盘压力
#PIDPressure磁盘压力
#Ready，是否就绪，表明节点是否处于正常工作状态，表示资源充足+相关进程状态正常
Type Status LastHeartbeatTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
MemoryPressure False Sun, 11 Aug 2019 20:32:07 +0800 Sat, 10 Aug 2019 17:50:00 +0800 KubeletHasSufficientMemory kubelet has sufficient memory available
DiskPressure False Sun, 11 Aug 2019 20:32:07 +0800 Sat, 10 Aug 2019 17:50:00 +0800 KubeletHasNoDiskPressure kubelet has no disk pressure
PIDPressure False Sun, 11 Aug 2019 20:32:07 +0800 Sat, 10 Aug 2019 17:50:00 +0800 KubeletHasSufficientPID kubelet has sufficient PID available
Ready True Sun, 11 Aug 2019 20:32:07 +0800 Sat, 10 Aug 2019 18:04:20 +0800 KubeletReady kubelet is posting ready status
Addresses: #地址和主机名
InternalIP: 10.254.100.103
Hostname: node-3
Capacity: #容器的资源容量
cpu: 2
ephemeral-storage: 51473868Ki
hugepages-2Mi: 0
memory: 3880524Ki
pods: 110
Allocatable: #已分配资源情况
cpu: 2
ephemeral-storage: 47438316671
hugepages-2Mi: 0
memory: 3778124Ki
pods: 110
System Info: #系统信息，如内核版本，操作系统版本，cpu架构，node节点软件版本
Machine ID: 0ea734564f9a4e2881b866b82d679dfc
System UUID: D98ECAB1-2D9E-41CC-9A5E-51A44DC5BB97
Boot ID: 6ec81f5b-cb05-4322-b47a-a8e046d9bf79
Kernel Version: 3.10.0-957.el7.x86_64
OS Image: CentOS Linux 7 (Core)
Operating System: linux
Architecture: amd64
Container Runtime Version: docker://18.3.1 . #Container Runtime为docker，版本为18.3.1
Kubelet Version: v1.14.1 #kubelet版本
Kube-Proxy Version: v1.14.1 #kube-proxy版本
PodCIDR: 10.244.2.0/24 #pod使用的网络
Non-terminated Pods: (4 in total)。 #下面是每个pod资源占用情况
Namespace Name CPU Requests CPU Limits Memory Requests Memory Limits AGE
--------- ---- ------------ ---------- --------------- ------------- ---
kube-system coredns-fb8b8dccf-hrqm8 100m (5%) 0 (0%) 70Mi (1%) 170Mi (4%) 26h
kube-system coredns-fb8b8dccf-qwwks 100m (5%) 0 (0%) 70Mi (1%) 170Mi (4%) 26h
kube-system kube-flannel-ds-amd64-zzm2g 100m (5%) 100m (5%) 50Mi (1%) 50Mi (1%) 26h
kube-system kube-proxy-x8zqh 0 (0%) 0 (0%) 0 (0%) 0 (0%) 26h
Allocated resources: #已分配资源情况
(Total limits may be over 100 percent, i.e., overcommitted.)
Resource Requests Limits
-------- -------- ------
cpu 300m (15%) 100m (5%)
memory 190Mi (5%) 390Mi (10%)
ephemeral-storage 0 (0%) 0 (0%)
Events: <none>
1.2 容器与应用
kubernetes是容器编排引擎，其负责容器的调度，管理和容器的运行，但kubernetes调度最小单位并非是container，而是pod，pod中可包含多个container，通常集群中不会直接运行pod，而是通过各种控制器如Deployments，ReplicaSets，DaemonSets的方式运行，为啥？因为控制器能够保证pod状态的一致性，正如官方所描述的一样“make sure the current state match to the desire state”，确保当前状态和预期的一致，简单来说就是pod异常了，控制器会在其他节点重建，确保集群当前运行的pod和预期设定的一致。
- Container，容器是一种轻量化的虚拟化技术，通过将应用封装在镜像中，实现便捷部署，应用分发。
- Pod，kubernetes中最小的调度单位，封装容器，包含一个pause容器和应用容器，容器之间共享相同的命名空间，网络，存储，共享进程。
- Deployments，部署组也称应用，严格上来说是无状态化应用，另外一种由状态化应用是StatefulSets，Deployments是一种控制器，可以控制应用的副本数replicas，通过kube-controller-manager中的Deployments Controller实现副本数状态的控制。
1.3 服务访问
kubernetes中pod是实际运行的载体，pod依附于node中，node可能会出现故障，kubernetes的控制器如replicasets会在其他node上重新拉起一个pod，新的pod会分配一个新的IP；再者，应用部署时会包含多个副本replicas，如同个应用deployments部署了3个pod副本，pod相当于后端的Real Server，如何实现这三个应用访问呢？对于这种情况，我们一般会在Real Server前面加一个负载均衡Load Balancer，service就是pod的负载均衡调度器，service将动态的pod抽象为一个服务，应用程序直接访问service即可，service会自动将请求转发到后端的pod。负责service转发规则有两种机制：iptables和ipvs，iptables通过设置DNAT等规则实现负载均衡，ipvs通过ipvsadm设置转发规。
根据服务不同的访问方式，service分为如下几种类型：ClusterIP，NodePort，LoadBalancer和_ExternalName，可通过type设置。
- ClusterIP，集群内部互访，与DNS结合实现集群内部的服务发现；
- NodePort，通过NAT将每个node节点暴露一个端口实现外部访问；
- LoadBalancer，实现云厂商外部接入方式的接口，需要依赖云服务提供商实现具体技术细节，如腾讯云实现与CLB集成；
-
ExternalName，通过服务名字暴露服务名，当前可由ingress实现，将外部的请求以域名转发的形式转发到集群，需要依附具体的外部实现，如nginx，traefik,各大云计算厂商实现接入细节。
pod是动态变化的，ip地址可能会变化（如node故障），副本数可能会变化，如应用扩展scale up，应用锁容scale down等，service如何识别到pod的动态变化呢？答案是labels，通过labels自动会过滤出某个应用的Endpoints，当pod变化时会自动更新Endpoints，不同的应用会有由不同的label组成。labels相关可以参考下https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/
2. 创建应用
我们开始部署一个应用即deployments，kubernetes中包含各种workload如无状态话的Deployments，有状态化的StatefulSets，守护进程的DaemonSets，美中workload对应不同的应用场景，我们先以Deployments为例入门，其他workload均以此类似，一般而言，在kubernetes中部署应用均以yaml文件方式部署，对于初学者而言，编写yaml文件太冗长，不适合初学，我们先kubectl命令行方式实现API的接入。
1、部署nginx应用，部署三个副本
[root@node-1 ~]# kubectl run nginx-app-demo --image=nginx:1.7.9 --port=80 --replicas=3
kubectl run --generator=deployment/apps.v1 is DEPRECATED and will be removed in a future version. Use kubectl run --generator=run-pod/v1 or kubectl create instead.
deployment.apps/nginx-app-demo created
2、查看应用列表,可以看到当前pod的状态均已正常，Ready是当前状态，AVAILABLE是目标状态
[root@node-1 ~]# kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
nginx-app-demo 3/3 3 3 72s
3、查看应用的详细信息,如下我们可以知道Deployments是通过ReplicaSets控制副本数的，由Replicaset控制pod数
[root@node-1 ~]# kubectl describe deployments nginx-app-demo
Name: nginx-app-demo #应用名称
Namespace: default #命名空间
CreationTimestamp: Sun, 11 Aug 2019 21:52:32 +0800
Labels: run=nginx-app-demo #labels，很重要，后续service通过labels实现访问
Annotations: deployment.kubernetes.io/revision: 1 #滚动升级版本号
Selector: run=nginx-app-demo #labels的选择器selector
Replicas: 3 desired | 3 updated | 3 total | 3 available | 0 unavailable #副本控制器
StrategyType: RollingUpdate #升级策略为RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge #RollingUpdate升级策略，即最大不超过25%的pod
Pod Template: #容器应用模版，包含镜像，port，存储等
Labels: run=nginx-app-demo
Containers:
nginx-app-demo:
Image: nginx:1.7.9
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions: #当前状态
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: nginx-app-demo-7bdfd97dcd (3/3 replicas created) #ReplicaSets控制器名称
Events: #运行事件
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 3m24s deployment-controller Scaled up replica set nginx-app-demo-7bdfd97dcd to 3
4、查看replicasets情况，通过查看可知replicasets副本控制器生成了三个pod
1. 查看replicasets列表
[root@node-1 ~]# kubectl get replicasets
NAME DESIRED CURRENT READY AGE
nginx-app-demo-7bdfd97dcd 3 3 3 9m9s
2. 查看replicasets详情
[root@node-1 ~]# kubectl describe replicasets nginx-app-demo-7bdfd97dcd
Name: nginx-app-demo-7bdfd97dcd
Namespace: default
Selector: pod-template-hash=7bdfd97dcd,run=nginx-app-demo
Labels: pod-template-hash=7bdfd97dcd #labels，增加了一个hash的label识别replicasets
run=nginx-app-demo
Annotations: deployment.kubernetes.io/desired-replicas: 3 #滚动升级的信息，副本树，最大数，应用版本
deployment.kubernetes.io/max-replicas: 4
deployment.kubernetes.io/revision: 1
Controlled By: Deployment/nginx-app-demo #副本的父控制，为nginx-app-demo这个Deployments
Replicas: 3 current / 3 desired
Pods Status: 3 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template: #容器模板，继承于deployments
Labels: pod-template-hash=7bdfd97dcd
run=nginx-app-demo
Containers:
nginx-app-demo:
Image: nginx:1.7.9
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Events: #事件日志，生成了三个不同的pod
Type Reason Age From Message
---- ------ ---- ---- -------
Normal SuccessfulCreate 9m25s replicaset-controller Created pod: nginx-app-demo-7bdfd97dcd-hsrft
Normal SuccessfulCreate 9m25s replicaset-controller Created pod: nginx-app-demo-7bdfd97dcd-qtbzd
Normal SuccessfulCreate 9m25s replicaset-controller Created pod: nginx-app-demo-7bdfd97dcd-7t72x
5、查看pod的情况,实际应用部署的载体，pod中部署了一个nginx的容器并分配了一个ip，可通过该ip直接访问应用
1. 查看pod的列表，和replicasets生成的名称一致
[root@node-1 ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-app-demo-7bdfd97dcd-7t72x 1/1 Running 0 13m
nginx-app-demo-7bdfd97dcd-hsrft 1/1 Running 0 13m
nginx-app-demo-7bdfd97dcd-qtbzd 1/1 Running 0 13m
查看pod的详情
[root@node-1 ~]# kubectl describe pods nginx-app-demo-7bdfd97dcd-7t72x
Name: nginx-app-demo-7bdfd97dcd-7t72x
Namespace: default
Priority: 0
PriorityClassName: <none>
Node: node-3/10.254.100.103
Start Time: Sun, 11 Aug 2019 21:52:32 +0800
Labels: pod-template-hash=7bdfd97dcd #labels名称
run=nginx-app-demo
Annotations: <none>
Status: Running
IP: 10.244.2.4 #pod的ip地址
Controlled By: ReplicaSet/nginx-app-demo-7bdfd97dcd #副本控制器为replicasets
Containers: #容器的信息，包括容器id，镜像，丢按扣，状态，环境变量等信息
nginx-app-demo:
Container ID: docker://5a0e5560583c5929e9768487cef43b045af4c6d3b7b927d9daf181cb28867766
Image: nginx:1.7.9
Image ID: docker-pullable://nginx@sha256:e3456c851a152494c3e4ff5fcc26f240206abac0c9d794affb40e0714846c451
Port: 80/TCP
Host Port: 0/TCP
State: Running
Started: Sun, 11 Aug 2019 21:52:40 +0800
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-txhkc (ro)
Conditions: #容器的状态条件
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes: #容器卷
default-token-txhkc:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-txhkc
Optional: false
QoS Class: BestEffort #QOS类型
Node-Selectors: <none> #污点类型
Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events: #事件状态，拉镜像，启动容器
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 14m default-scheduler Successfully assigned default/nginx-app-demo-7bdfd97dcd-7t72x to node-3
Normal Pulling 14m kubelet, node-3 Pulling image "nginx:1.7.9"
Normal Pulled 14m kubelet, node-3 Successfully pulled image "nginx:1.7.9"
Normal Created 14m kubelet, node-3 Created container nginx-app-demo
Normal Started 14m kubelet, node-3 Started container nginx-app-demo
3. 访问应用
kubernetes为每个pod都分配了一个ip地址，可通过该地址直接访问应用，相当于访问RS，但一个应用是一个整体，由多个副本数组成，需要依赖于service来实现应用的负载均衡，service我们探讨ClusterIP和NodePort的访问方式。
3.1 访问Pod IP
1、设置pod的内容，为了方便区分，我们将三个pod的nginx站点内容设置为不同，以观察负载均衡的效果
查看pod列表
[root@node-1 ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-app-demo-7bdfd97dcd-7t72x 1/1 Running 0 28m
nginx-app-demo-7bdfd97dcd-hsrft 1/1 Running 0 28m
nginx-app-demo-7bdfd97dcd-qtbzd 1/1 Running 0 28m
进入pod容器中
[root@node-1 ~]# kubectl exec -it nginx-app-demo-7bdfd97dcd-7t72x /bin/bash
设置站点内容
[root@nginx-app-demo-7bdfd97dcd-7t72x:/# echo "web1" >/usr/share/nginx/html/index.html
以此类推设置另外两个pod的内容为web2和web3
[root@nginx-app-demo-7bdfd97dcd-hsrft:/# echo web2 >/usr/share/nginx/html/index.html
[root@nginx-app-demo-7bdfd97dcd-qtbzd:/# echo web3 >/usr/share/nginx/html/index.html
2、获取pod的ip地址，如何快速获取pod的ip地址呢，可以通过-o wide参数显示更多的内容,会包含pod所属node和ip
[root@node-1 ~]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-app-demo-7bdfd97dcd-7t72x 1/1 Running 0 34m 10.244.2.4 node-3 <none> <none>
nginx-app-demo-7bdfd97dcd-hsrft 1/1 Running 0 34m 10.244.1.2 node-2 <none> <none>
nginx-app-demo-7bdfd97dcd-qtbzd 1/1 Running 0 34m 10.244.1.3 node-2 <none> <none>
3、访问pod的ip，查看站点内容,不同的pod站点内容和上述步骤设置一致。
[root@node-1 ~]# curl http://10.244.2.4
web1
[root@node-1 ~]# curl http://10.244.1.2
web2
[root@node-1 ~]# curl http://10.244.1.3
web3
3.2 ClusterIP访问
通过pod的ip直接访问应用，对于单个pod的应用可以实现，对于多个副本replicas的应用则不符合要求，需要通过service来实现负载均衡，service需要设置不同的type，默认为ClusterIP即集群内部访问，如下通过expose子命令将服务暴露到service。
1、暴露service,其中port表示代理监听端口，target-port代表是容器的端口，type设置的是service的类型
[root@node-1 ~]# kubectl expose deployment nginx-app-demo --name nginx-service-demo \
--port=80 \
--protocol=TCP \
--target-port=80 \
--type ClusterIP
service/nginx-service-demo exposed
2、查看service的详情，可以看到service通过labels选择器selector自动将pod的ip生成endpoints
查看service列表，显示有两个，kubernetes为默认集群创建的service
[root@node-1 ~]# kubectl get services
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 29h
nginx-service-demo ClusterIP 10.102.1.1 <none> 80/TCP 2m54s
查看service详情，可以看到Labels的Seletor和前面Deployments设置一致，Endpoints将pod组成一个列表
[root@node-1 ~]# kubectl describe services nginx-service-demo
Name: nginx-service-demo #名称
Namespace: default #命名空间
Labels: run=nginx-app-demo #标签名称
Annotations: <none>
Selector: run=nginx-app-demo #标签选择器
Type: ClusterIP #service类型为ClusterIP
IP: 10.102.1.1 #服务的ip，即vip，集群内部会自动分配一个
Port: <unset> 80/TCP #服务端口，即ClusterIP对外访问的端口
TargetPort: 80/TCP #容器端口
Endpoints: 10.244.1.2:80,10.244.1.3:80,10.244.2.4:80 #访问地址列表
Session Affinity: None #负载均衡调度算法
Events: <none>
3、访问service的地址，可以访问的内容可知，service自动实现了pods的负载均衡，调度策略为轮询，为何？因为service默认的调度策略Session Affinity为None，即是轮训，可以设置为ClientIP，实现会话保持，相同客户端IP的请求会调度到相同的pod上。
[root@node-1 ~]# curl http://10.102.1.1
web3
[root@node-1 ~]# curl http://10.102.1.1
web1
[root@node-1 ~]# curl http://10.102.1.1
web2
[root@node-1 ~]# curl http://10.102.1.1
4、ClusterIP原理深入剖析，service后端实现有两种机制：iptables和ipvs，环境安装采用iptables，iptables通过nat的链生成访问规则，KUBE-SVC-R5Y5DZHD7Q6DDTFZ为入站DNAT转发规则，KUBE-MARK-MASQ为出站转发
[root@node-1 ~]# iptables -t nat -L -n
Chain KUBE-SERVICES (2 references)
target prot opt source destination
KUBE-MARK-MASQ tcp -- !10.244.0.0/16 10.102.1.1 /* default/nginx-service-demo: cluster IP */ tcp dpt:80
KUBE-SVC-R5Y5DZHD7Q6DDTFZ tcp -- 0.0.0.0/0 10.102.1.1 /* default/nginx-service-demo: cluster IP */ tcp dpt:80
出站：KUBE-MARK-MASQ源地址段不是10.244.0.0/16访问10.102.1.1的目标端口80时，将请求转发给KUBE-MARK-MASQ链
入站：KUBE-SVC-R5Y5DZHD7Q6DDTFZ任意原地址访问目标10.102.1.1的目标端口80时将请求转发给KUBE-SVC-R5Y5DZHD7Q6DDTFZ链
5、查看入站请求规则，入站请求规则将会映射到不同的链，不同链将会转发到不同pod的ip上。
1. 查看入站规则KUBE-SVC-R5Y5DZHD7Q6DDTFZ，请求将转发至三条链
[root@node-1 ~]# iptables -t nat -L KUBE-SVC-R5Y5DZHD7Q6DDTFZ -n
Chain KUBE-SVC-R5Y5DZHD7Q6DDTFZ (1 references)
target prot opt source destination
KUBE-SEP-DSWLUQNR4UPH24AX all -- 0.0.0.0/0 0.0.0.0/0 statistic mode random probability 0.33332999982
KUBE-SEP-56SLMGHHOILJT36K all -- 0.0.0.0/0 0.0.0.0/0 statistic mode random probability 0.50000000000
KUBE-SEP-K6G4Z74HQYF6X7SI all -- 0.0.0.0/0 0.0.0.0/0
2. 查看实际转发的三条链的规则,实际映射到不同的pod的ip地址上
[root@node-1 ~]# iptables -t nat -L KUBE-SEP-DSWLUQNR4UPH24AX -n
Chain KUBE-SEP-DSWLUQNR4UPH24AX (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.1.2 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp to:10.244.1.2:80
[root@node-1 ~]# iptables -t nat -L KUBE-SEP-56SLMGHHOILJT36K -n
Chain KUBE-SEP-56SLMGHHOILJT36K (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.1.3 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp to:10.244.1.3:80
[root@node-1 ~]# iptables -t nat -L KUBE-SEP-K6G4Z74HQYF6X7SI -n
Chain KUBE-SEP-K6G4Z74HQYF6X7SI (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.2.4 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp to:10.244.2.4:80
3.3 NodePort访问
Service通过ClusterIP只能提供集群内部的应用访问，外部无法直接访问应用，如果需要外部访问有如下几种方式：NodePort，LoadBalancer和Ingress，其中LoadBalancer需要由云服务提供商实现，Ingress需要安装单独的Ingress Controller，日常测试可以通过NodePort的方式实现，NodePort可以将node的某个端口暴露给外部网络访问。
1、修改type的类型由ClusterIP修改为NodePort类型（或者重新创建，指定type的类型为NodePort）
1. 通过patch修改type的类型
[root@node-1 ~]# kubectl patch services nginx-service-demo -p '{"spec":{"type": "NodePort"}}'
service/nginx-service-demo patched
2. 确认yaml文件配置，分配了一个NodePort端口，即每个node上都会监听该端口
[root@node-1 ~]# kubectl get services nginx-service-demo -o yaml
apiVersion: v1
kind: Service
metadata:
creationTimestamp: "2019-08-11T14:35:59Z"
labels:
run: nginx-app-demo
name: nginx-service-demo
namespace: default
resourceVersion: "157676"
selfLink: /api/v1/namespaces/default/services/nginx-service-demo
uid: 55e29b78-bc45-11e9-b073-525400490421
spec:
clusterIP: 10.102.1.1
externalTrafficPolicy: Cluster
ports:
- nodePort: 32416 #自动分配了一个NodePort端口
port: 80
protocol: TCP
targetPort: 80
selector:
run: nginx-app-demo
sessionAffinity: None
type: NodePort #类型修改为NodePort
status:
loadBalancer: {}
3. 查看service列表，可以知道service的type已经修改为NodePort,同时还保留ClusterIP的访问IP
[root@node-1 ~]# kubectl get services
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 30h
nginx-service-demo NodePort 10.102.1.1 <none> 80:32416/TCP 68m
2、通过NodePort访问应用程序,每个node的地址相当于vip，可以实现相同的负载均衡效果，同时CluserIP功能依可用
1. NodePort的负载均衡
[root@node-1 ~]# curl http://node-1:32416
web1
[root@node-1 ~]# curl http://node-2:32416
web1
[root@node-1 ~]# curl http://node-3:32416
web1
[root@node-1 ~]# curl http://node-3:32416
web3
[root@node-1 ~]# curl http://node-3:32416
web2
2. ClusterIP的负载均衡
[root@node-1 ~]# curl http://10.102.1.1
web2
[root@node-1 ~]# curl http://10.102.1.1
web1
[root@node-1 ~]# curl http://10.102.1.1
web1
[root@node-1 ~]# curl http://10.102.1.1
web3
3、NodePort转发原理，每个node上通过kube-proxy监听NodePort的端口，由后端的iptables实现端口的转发
1. NodePort监听端口
[root@node-1 ~]# netstat -antupl |grep 32416
tcp6 0 0 :::32416 :::* LISTEN 32052/kube-proxy
2. 查看nat表的转发规则，有两条规则KUBE-MARK-MASQ出口和KUBE-SVC-R5Y5DZHD7Q6DDTFZ入站方向。
Chain KUBE-NODEPORTS (1 references)
target prot opt source destination
KUBE-MARK-MASQ tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/nginx-service-demo: */ tcp dpt:32416
KUBE-SVC-R5Y5DZHD7Q6DDTFZ tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/nginx-service-demo: */ tcp dpt:32416
3. 查看入站的请求规则链KUBE-SVC-R5Y5DZHD7Q6DDTFZ
[root@node-1 ~]# iptables -t nat -L KUBE-SVC-R5Y5DZHD7Q6DDTFZ -n
Chain KUBE-SVC-R5Y5DZHD7Q6DDTFZ (2 references)
target prot opt source destination
KUBE-SEP-DSWLUQNR4UPH24AX all -- 0.0.0.0/0 0.0.0.0/0 statistic mode random probability 0.33332999982
KUBE-SEP-56SLMGHHOILJT36K all -- 0.0.0.0/0 0.0.0.0/0 statistic mode random probability 0.50000000000
KUBE-SEP-K6G4Z74HQYF6X7SI all -- 0.0.0.0/0 0.0.0.0/0
4. 继续查看转发链，包含有DNAT转发和KUBE-MARK-MASQ和出站返回的规则
[root@node-1 ~]# iptables -t nat -L KUBE-SEP-DSWLUQNR4UPH24AX -n
Chain KUBE-SEP-DSWLUQNR4UPH24AX (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.1.2 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp to:10.244.1.2:80
[root@node-1 ~]# iptables -t nat -L KUBE-SEP-56SLMGHHOILJT36K -n
Chain KUBE-SEP-56SLMGHHOILJT36K (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.1.3 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp to:10.244.1.3:80
[root@node-1 ~]# iptables -t nat -L KUBE-SEP-K6G4Z74HQYF6X7SI -n
Chain KUBE-SEP-K6G4Z74HQYF6X7SI (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.2.4 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp to:10.244.2.4:80
4. 扩展应用
当应用程序的负载比较高无法满足应用请求时，一般我们会通过扩展RS的数量来实现，在kubernetes中，扩展RS实际上通过扩展副本数replicas来实现，扩展RS非常便利，快速实现弹性伸缩。kubernets能提供两种方式的伸缩能力：1. 手动伸缩能力scale up和scale down，2. 动态的弹性伸缩horizontalpodautoscalers,基于CPU的利用率实现自动的弹性伸缩，需要依赖与监控组件如metrics server，当前未实现，后续再做深入探讨，本文以手动的scale的方式扩展应用的副本数。
1、手动扩展副本数
[root@node-1 ~]# kubectl scale --replicas=4 deployment nginx-app-demo
deployment.extensions/nginx-app-demo scaled
2、查看副本扩展情况,deployments自动部署一个应用
[root@node-1 ~]# kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
nginx-app-demo 4/4 4 4 133m
3、此时service的情况会怎样呢？查看service详情,新扩展的pod会自动更新到service的endpoints中，自动服务发现
查看service详情
[root@node-1 ~]# kubectl describe services nginx-service-demo
Name: nginx-service-demo
Namespace: default
Labels: run=nginx-app-demo
Annotations: <none>
Selector: run=nginx-app-demo
Type: NodePort
IP: 10.102.1.1
Port: <unset> 80/TCP
TargetPort: 80/TCP
NodePort: <unset> 32416/TCP
Endpoints: 10.244.1.2:80,10.244.1.3:80,10.244.2.4:80 + 1 more...#地址已自动加入
Session Affinity: None
External Traffic Policy: Cluster
Events: <none>
查看endpioints详情
[root@node-1 ~]# kubectl describe endpoints nginx-service-demo
Name: nginx-service-demo
Namespace: default
Labels: run=nginx-app-demo
Annotations: endpoints.kubernetes.io/last-change-trigger-time: 2019-08-11T16:04:56Z
Subsets:
Addresses: 10.244.1.2,10.244.1.3,10.244.2.4,10.244.2.5
NotReadyAddresses: <none>
Ports:
Name Port Protocol
---- ---- --------
<unset> 80 TCP
Events: <none>
4、测试，将新加入的pod站点内容设置为web4，参考前面的设置方法，测试service的ip，查看负载均衡效果
[root@node-1 ~]# curl http://10.102.1.1
web4
[root@node-1 ~]# curl http://10.102.1.1
web4
[root@node-1 ~]# curl http://10.102.1.1
web2
[root@node-1 ~]# curl http://10.102.1.1
web3
[root@node-1 ~]# curl http://10.102.1.1
web1
[root@node-1 ~]# curl http://10.102.1.1
web2
[root@node-1 ~]# curl http://10.102.1.1
web1
由此可知，弹性伸缩会自动自动加入到service中实现服务自动发现和负载均衡，应用的扩展相比于传统应用快速非常多。
5. 滚动升级
在kubernetes中更新应用程序时可以将应用程序打包到镜像中，然后更新应用程序的镜像以实现升级。默认Deployments的升级策略为RollingUpdate，其每次会更新应用中的25%的pod，新建新的pod逐个替换，防止应用程序在升级过程中不可用。同时，如果应用程序升级过程中失败，还可以通过回滚的方式将应用程序回滚到之前的状态，回滚时通过replicasets的方式实现。
1、更换nginx的镜像，将应用升级至最新版本,打开另外一个窗口使用kubectl get pods -w观察升级过程
[root@node-1 ~]# kubectl set image deployments/nginx-app-demo nginx-app-demo=nginx:latest
deployment.extensions/nginx-app-demo image updated
2、观察升级过程，通过查看可知，升级过程中是通过新建+删除的方式逐个替换pod的方式
[root@node-1 ~]# kubectl get pods -w
NAME READY STATUS RESTARTS AGE
nginx-app-demo-7bdfd97dcd-7t72x 1/1 Running 0 145m
nginx-app-demo-7bdfd97dcd-hsrft 1/1 Running 0 145m
nginx-app-demo-7bdfd97dcd-j6lgd 1/1 Running 0 12m
nginx-app-demo-7bdfd97dcd-qtbzd 1/1 Running 0 145m
nginx-app-demo-5cc8746f96-xsxz4 0/1 Pending 0 0s #新建一个pod
nginx-app-demo-5cc8746f96-xsxz4 0/1 Pending 0 0s
nginx-app-demo-7bdfd97dcd-j6lgd 1/1 Terminating 0 14m #删除旧的pod，替换
nginx-app-demo-5cc8746f96-xsxz4 0/1 ContainerCreating 0 0s
nginx-app-demo-5cc8746f96-s49nv 0/1 Pending 0 0s #新建第二个pod
nginx-app-demo-5cc8746f96-s49nv 0/1 Pending 0 0s
nginx-app-demo-5cc8746f96-s49nv 0/1 ContainerCreating 0 0s
nginx-app-demo-7bdfd97dcd-j6lgd 0/1 Terminating 0 14m #更换第二个pod
nginx-app-demo-5cc8746f96-s49nv 1/1 Running 0 7s
nginx-app-demo-7bdfd97dcd-qtbzd 1/1 Terminating 0 146m
nginx-app-demo-5cc8746f96-txjqh 0/1 Pending 0 0s
nginx-app-demo-5cc8746f96-txjqh 0/1 Pending 0 0s
nginx-app-demo-5cc8746f96-txjqh 0/1 ContainerCreating 0 0s
nginx-app-demo-7bdfd97dcd-j6lgd 0/1 Terminating 0 14m
nginx-app-demo-7bdfd97dcd-j6lgd 0/1 Terminating 0 14m
nginx-app-demo-5cc8746f96-xsxz4 1/1 Running 0 9s
nginx-app-demo-5cc8746f96-txjqh 1/1 Running 0 1s
nginx-app-demo-7bdfd97dcd-hsrft 1/1 Terminating 0 146m
nginx-app-demo-7bdfd97dcd-qtbzd 0/1 Terminating 0 146m
nginx-app-demo-5cc8746f96-rcpmw 0/1 Pending 0 0s
nginx-app-demo-5cc8746f96-rcpmw 0/1 Pending 0 0s
nginx-app-demo-5cc8746f96-rcpmw 0/1 ContainerCreating 0 0s
nginx-app-demo-7bdfd97dcd-7t72x 1/1 Terminating 0 146m
nginx-app-demo-7bdfd97dcd-7t72x 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-hsrft 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-hsrft 0/1 Terminating 0 147m
nginx-app-demo-5cc8746f96-rcpmw 1/1 Running 0 2s
nginx-app-demo-7bdfd97dcd-7t72x 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-7t72x 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-hsrft 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-hsrft 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-qtbzd 0/1 Terminating 0 147m
nginx-app-demo-7bdfd97dcd-qtbzd 0/1 Terminating 0 147m
3、再次查看deployments的详情可知道，deployments已经更换了新的replicasets，原来的replicasets的版本为1，可用于回滚。
[root@node-1 ~]# kubectl describe deployments nginx-app-demo
Name: nginx-app-demo
Namespace: default
CreationTimestamp: Sun, 11 Aug 2019 21:52:32 +0800
Labels: run=nginx-app-demo
Annotations: deployment.kubernetes.io/revision: 2 #新的版本号，用于回滚
Selector: run=nginx-app-demo
Replicas: 4 desired | 4 updated | 4 total | 4 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: run=nginx-app-demo
Containers:
nginx-app-demo:
Image: nginx:latest
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: nginx-app-demo-5cc8746f96 (4/4 replicas created) #新的replicaset，实际是替换新的replicasets
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 19m deployment-controller Scaled up replica set nginx-app-demo-7bdfd97dcd to 4
Normal ScalingReplicaSet 4m51s deployment-controller Scaled up replica set nginx-app-demo-5cc8746f96 to 1
Normal ScalingReplicaSet 4m51s deployment-controller Scaled down replica set nginx-app-demo-7bdfd97dcd to 3
Normal ScalingReplicaSet 4m51s deployment-controller Scaled up replica set nginx-app-demo-5cc8746f96 to 2
Normal ScalingReplicaSet 4m43s deployment-controller Scaled down replica set nginx-app-demo-7bdfd97dcd to 2
Normal ScalingReplicaSet 4m43s deployment-controller Scaled up replica set nginx-app-demo-5cc8746f96 to 3
Normal ScalingReplicaSet 4m42s deployment-controller Scaled down replica set nginx-app-demo-7bdfd97dcd to 1
Normal ScalingReplicaSet 4m42s deployment-controller Scaled up replica set nginx-app-demo-5cc8746f96 to 4
Normal ScalingReplicaSet 4m42s deployment-controller Scaled down replica set nginx-app-demo-7bdfd97dcd to 0
4、查看滚动升级的版本，可以看到有两个版本，分别对应的两个不同的replicasets
[root@node-1 ~]# kubectl rollout history deployment nginx-app-demo
deployment.extensions/nginx-app-demo
REVISION CHANGE-CAUSE
1 <none>
2 <none>
查看replicasets列表,旧的包含pod为0
[root@node-1 ~]# kubectl get replicasets
NAME DESIRED CURRENT READY AGE
nginx-app-demo-5cc8746f96 4 4 4 9m2s
nginx-app-demo-7bdfd97dcd 0 0 0 155m
5、测试应用的升级情况,发现nginx已经升级到最新nginx/1.17.2版本
[root@node-1 ~]# curl -I http://10.102.1.1
HTTP/1.1 200 OK
Server: nginx/1.17.2 #nginx版本信息
Date: Sun, 11 Aug 2019 16:30:03 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Tue, 23 Jul 2019 11:45:37 GMT
Connection: keep-alive
ETag: "5d36f361-264"
Accept-Ranges: bytes
6、回滚到旧的版本
[root@node-1 ~]# kubectl rollout undo deployment nginx-app-demo --to-revision=1
deployment.extensions/nginx-app-demo rolled back
再次测应用,已经回滚到旧版本。
[root@node-1 ~]# curl -I http://10.102.1.1
HTTP/1.1 200 OK
Server: nginx/1.7.9
Date: Sun, 11 Aug 2019 16:34:33 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Tue, 23 Dec 2014 16:25:09 GMT
Connection: keep-alive
ETag: "54999765-264"
Accept-Ranges: bytes
写在最后：本文以命令行的方式实践探索kubernetes中涉及的最重要的几个概念：应用部署，负载均衡，弹性伸缩和滚动升级，并以命令行的形式实际操作，读者可以参照文档实现快速入门，后续会大部分以yaml文件的形式部署和kubernets交互。
参考文档
基础概念：https://kubernetes.io/docs/tutorials/kubernetes-basics/
部署应用：https://kubernetes.io/docs/tutorials/kubernetes-basics/deploy-app/deploy-intro/
访问应用：https://kubernetes.io/docs/tutorials/kubernetes-basics/explore/explore-intro/
外部访问：https://kubernetes.io/docs/tutorials/kubernetes-basics/expose/expose-intro/
访问应用：https://kubernetes.io/docs/tutorials/kubernetes-basics/scale/scale-intro/
滚动升级：https://kubernetes.io/docs/tutorials/kubernetes-basics/update/update-intro/
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