基于Kubernetes和Docke实现留言簿案例

一、介绍

本案例基于kubernetes和docker，其中包括
1、web前端
2、redis master
3、redis slave
其中web前端通过javascript redis api和redis master交互

kubernetes体系架构

二、配置

0、先决条件
kubernetes 集群

1、启动redis master
使用replication controller确保只有一个pod在运行（当某个节点down了，rc会在另一个健康的node启动redis master），但可能会有数据丢失。

[root@centos1 example]# kubectl create -f redis-master-controller.json 
replicationcontrollers/redis-master
[root@centos1 example]# kubectl get rc
controller   container(s)  image(s)  selector      replicas
redis-master  master     redis   name=redis-master  1

验证master运行成功，如下展示了pod运行在centos2/192.168.1.112这台机器上   

[root@centos1 example]# kubectl get pods
pod         ip      container(s)  image(s)  host          labels       status  created   message
redis-master-svar7  172.17.0.9               centos2/192.168.1.112  name=redis-master  running  55 seconds  
                 master     redis                         running  55 seconds  

ssh到centos2/192.168.1.112查看docker状态

[root@centos2 yum.repos.d]# docker ps
container id    image                 command        created       status       ports        names
91689ce56668    redis:latest              "/entrypoint.sh redi  3 minutes ago    up 3 minutes              k8s_master.52732b08_redis-master-svar7_default_5b6d5485-1894-11e5-b3ad-000c293c8c19_97e79b7b  
38c3180813c3    gcr.io/google_containers/pause:0.8.0  "/pause"        3 minutes ago    up 3 minutes              k8s_pod.49eee8c2_redis-master-svar7_default_5b6d5485-1894-11e5-b3ad-000c293c8c19_298e038f   

注意：kubectl create执行后，如果镜像不存在，会执行docker pull，根据网络情况，下载中的pods 在kubertnetes ui上会显示pending状态

2、启动master service
一个kubernetes service会对一个或多个container进行负载均衡，这是通过我们上面redis-master中定义的labels元数据实现的，值得注意的是，在redis中只有一个master，但是我们依然为它创建一个service，这是因为这样我们就能使用一个elastic ip来路由到具体某一个master。
kubernetes集群中的service是通过container中的环境变量实现服务发现的，service基于pod label实现container的负载均衡。
在第一步中创建的pod包含了一个label“name=redis-master”，service的selector字段决定了service将流量转发给哪个pod，port和targetport信息定义了service proxy运行在什么端口。

[root@centos1 example]# kubectl create -f redis-master-service.json 
services/redis-master
[root@centos1 example]# kubectl get services
name      labels                  selector      ip(s)      port(s)
redis-master  name=redis-master             name=redis-master  10.254.154.90  6379/tcp

上面的运行成功后，所有pods都能发现redis master运行在6379端口，从salve到master流量走向会有以下两步：
1、一个redis slave会连接到redis master service的port上
2、流量会从service节点上的port到targetport
如果targetport未指定，默认和port一致

3、启动replicated slave pod
虽然redis master是一个单独的pod，redis slaves是一个replicated pod，在kubernetes中，一个replication controller负责管理一个replicated pod的多个实例，rc会自动拉起down掉的replica（可以通过杀死docker 进程方式简单测试）

[root@centos1 example]# kubectl create -f redis-slave-controller.json 
replicationcontrollers/redis-slave
[root@centos1 example]# kubectl get rc
controller   container(s)  image(s)          selector      replicas
redis-master  master     redis            name=redis-master  1
redis-slave  slave     kubernetes/redis-slave:v2  name=redis-slave  2
[root@centos1 example]# kubectl get pods
pod         ip      container(s)  image(s)          host          labels       status  created   message
redis-master-svar7  172.17.0.9                        centos2/192.168.1.112  name=redis-master  running  41 minutes  
                  master     redis                                  running  41 minutes  
redis-slave-31tkb  172.17.0.10                       centos2/192.168.1.112  name=redis-slave  running  29 seconds  
                  slave     kubernetes/redis-slave:v2                        running  28 seconds  
redis-slave-uk8nu  172.17.0.11                       centos2/192.168.1.112  name=redis-slave  running  29 seconds  
                  slave     kubernetes/redis-slave:v2                        running  28 seconds  

可以看到一个master pod和两个slave pod

4、启动slave service
和master一样，我们希望有一个代理服务连接到redis slave，除了服务发现之外，slave service还为web app client提供了透明代理。
这次service 的selector是name=redis-slave，我们可以方便的使用kubectl get services -l "label=value"命令来定位这些服务

[root@centos1 example]# kubectl create -f redis-slave-service.json 
services/redis-slave
[root@centos1 example]# kubectl get services
name      labels                  selector      ip(s)      port(s)
redis-master  name=redis-master             name=redis-master  10.254.154.90  6379/tcp
redis-slave   name=redis-slave             name=redis-slave  10.254.159.145  6379/tcp

5、创建frontend pod
这是一个简单的php 服务，用来和master service（写请求）或slave service（读请求）交互

[root@centos1 example]# kubectl create -f frontend-controller.json 
replicationcontrollers/frontend
[root@centos1 example]# kubectl get rc
controller   container(s)  image(s)                  selector      replicas
frontend    php-redis   kubernetes/example-guestbook-php-redis:v2  name=frontend    3
redis-master  master     redis                    name=redis-master  1
redis-slave  slave     kubernetes/redis-slave:v2          name=redis-slave  2

运行成功后，查看当前pod运行状态

[root@centos1 example]# kubectl get pods
pod         ip      container(s)  image(s)                  host          labels       status  created   message
frontend-fr5z1    172.17.0.13                               centos2/192.168.1.112  name=frontend    running  2 minutes  
                  php-redis   kubernetes/example-guestbook-php-redis:v2                        running  2 minutes  
frontend-gjx3t    172.17.0.14                               centos2/192.168.1.112  name=frontend    running  2 minutes  
                  php-redis   kubernetes/example-guestbook-php-redis:v2                        running  2 minutes  
frontend-v608r    172.17.0.12                               centos2/192.168.1.112  name=frontend    running  2 minutes  
                  php-redis   kubernetes/example-guestbook-php-redis:v2                        running  2 minutes  
redis-master-svar7  172.17.0.9                                centos2/192.168.1.112  name=redis-master  running  53 minutes  
                  master     redis                                          running  53 minutes  
redis-slave-31tkb  172.17.0.10                               centos2/192.168.1.112  name=redis-slave  running  12 minutes  
                  slave     kubernetes/redis-slave:v2                                running  12 minutes  
redis-slave-uk8nu  172.17.0.11                               centos2/192.168.1.112  name=redis-slave  running  12 minutes  
                  slave     kubernetes/redis-slave:v2                                running  12 minutes  

可以看到一个redis master，两个redis slave和三个frontend pods

6、创建guestbook service
和其他service一样，你可以创建一个service管理frontend pods

[root@centos1 example]# kubectl create -f frontend-service.json 
services/frontend
[root@centos1 example]# kubectl get services
name      labels                  selector      ip(s)      port(s)
frontend    name=frontend               name=frontend    10.254.154.111  80/tcp
redis-master  name=redis-master             name=redis-master  10.254.154.90  6379/tcp
redis-slave   name=redis-slave             name=redis-slave  10.254.159.145  6379/tcp

我们可以通过frontend service（10.254.154.111）访问pods，但是这个ip明显是无法在外部访问的，下一节讲解如何在外部网络访问guestbook

7、外部网络访问guestbook
kubernetes 支持两种访问暴露一个服务到外部ip地址nodeports 和loadbalancers，另外可以查看防火墙，找到service对应的端口，如下

[root@centos1 example]# kubectl get pods,services
pod         ip      container(s)  image(s)                  host          labels       status  created     message
frontend-fr5z1    172.17.0.13                               centos2/192.168.1.112  name=frontend    running  22 minutes   
                  php-redis   kubernetes/example-guestbook-php-redis:v2                        running  22 minutes   
frontend-gjx3t    172.17.0.14                               centos2/192.168.1.112  name=frontend    running  22 minutes   
                  php-redis   kubernetes/example-guestbook-php-redis:v2                        running  22 minutes   
frontend-v608r    172.17.0.12                               centos2/192.168.1.112  name=frontend    running  22 minutes   
                  php-redis   kubernetes/example-guestbook-php-redis:v2                        running  22 minutes   
redis-master-svar7  172.17.0.9                                centos2/192.168.1.112  name=redis-master  running  about an hour  
                  master     redis                                          running  about an hour  
redis-slave-31tkb  172.17.0.10                               centos2/192.168.1.112  name=redis-slave  running  32 minutes   
                  slave     kubernetes/redis-slave:v2                                running  32 minutes   
redis-slave-uk8nu  172.17.0.11                               centos2/192.168.1.112  name=redis-slave  running  32 minutes   
                  slave     kubernetes/redis-slave:v2                                running  32 minutes   
name      labels                  selector      ip(s)      port(s)
frontend    name=frontend               name=frontend    10.254.154.111  80/tcp
kubernetes   component=apiserver,provider=kubernetes  <none>       10.254.0.2    443/tcp
kubernetes-ro  component=apiserver,provider=kubernetes  <none>       10.254.0.1    80/tcp
redis-master  name=redis-master             name=redis-master  10.254.154.90  6379/tcp
redis-slave   name=redis-slave             name=redis-slave  10.254.159.145  6379/tcp
[root@centos1 example]# kubectl get services
name      labels                  selector      ip(s)      port(s)
frontend    name=frontend               name=frontend    10.254.154.111  80/tcp
kubernetes   component=apiserver,provider=kubernetes  <none>       10.254.0.2    443/tcp
kubernetes-ro  component=apiserver,provider=kubernetes  <none>       10.254.0.1    80/tcp
redis-master  name=redis-master             name=redis-master  10.254.154.90  6379/tcp
redis-slave   name=redis-slave             name=redis-slave  10.254.159.145  6379/tcp

发现redis-master是在10.254.154.90上，登录到centos2上，执行iptables-save，发现其中有这样一条规则

-a kube-portals-host -d 10.254.154.90/32 -p tcp -m comment --comment "default/redis-master:" -m tcp --dport 6379 -j dnat --to-destination 192.168.1.112:49038

说明，centos2本机的49038端口映射到master container内的6379了，当然我们就能执行在本机访问redis了

[root@centos2 yum.repos.d]# redis-cli -p 49038
127.0.0.1:49038> set a b
ok
127.0.0.1:49038> get a
"b"

8、使用curl简单测试

提交数据

curl "localhost:8000/index.php?cmd=set&key=messages&value=jay_sais_hi"

查询数据

curl "localhost:8000/index.php?cmd=get&key=messages"

附本案例用到的6个.json文件
1、redis-master-controller.json

{
  "kind":"replicationcontroller",
  "apiversion":"v1beta3",
  "metadata":{
   "name":"redis-master",
   "labels":{
     "name":"redis-master"
   }
  },
  "spec":{
   "replicas":1,
   "selector":{
     "name":"redis-master"
   },
   "template":{
     "metadata":{
      "labels":{
        "name":"redis-master"
      }
     },
     "spec":{
      "containers":[
        {
         "name":"master",
         "image":"redis",
         "ports":[
           {
            "containerport":6379
           }
         ]
        }
      ]
     }
   }
  }
}

2、redis-master-service.json

{
  "kind":"service",
  "apiversion":"v1beta3",
  "metadata":{
   "name":"redis-master",
   "labels":{
     "name":"redis-master"
   }
  },
  "spec":{
   "ports": [
    {
     "port":6379,
     "targetport":6379
    }
   ],
   "selector":{
     "name":"redis-master"
   }
  }
}

3、redis-slave-controller.json

{
  "kind":"replicationcontroller",
  "apiversion":"v1beta3",
  "metadata":{
   "name":"redis-slave",
   "labels":{
     "name":"redis-slave"
   }
  },
  "spec":{
   "replicas":2,
   "selector":{
     "name":"redis-slave"
   },
   "template":{
     "metadata":{
      "labels":{
        "name":"redis-slave"
      }
     },
     "spec":{
      "containers":[
        {
         "name":"slave",
         "image":"kubernetes/redis-slave:v2",
         "ports":[
           {
            "containerport":6379
           }
         ]
        }
      ]
     }
   }
  }
}

4、redis-slave-service.json

{
  "kind":"service",
  "apiversion":"v1beta3",
  "metadata":{
   "name":"redis-slave",
   "labels":{
     "name":"redis-slave"
   }
  },
  "spec":{
   "ports": [
    {
     "port":6379
    }
   ],
   "selector":{
     "name":"redis-slave"
   }
  }
}

5、frontend-controller.json

{
  "kind":"replicationcontroller",
  "apiversion":"v1beta3",
  "metadata":{
   "name":"frontend",
   "labels":{
     "name":"frontend"
   }
  },
  "spec":{
   "replicas":3,
   "selector":{
     "name":"frontend"
   },
   "template":{
     "metadata":{
      "labels":{
        "name":"frontend"
      }
     },
     "spec":{
      "containers":[
        {
         "name":"php-redis",
         "image":"kubernetes/example-guestbook-php-redis:v2",
         "ports":[
           {
            "containerport":80
           }
         ]
        }
      ]
     }
   }
  }
}

6、frontend-service.json

{
  "kind":"service",
  "apiversion":"v1beta3",
  "metadata":{
   "name":"frontend",
   "labels":{
     "name":"frontend"
   }
  },
  "spec":{
   "ports": [
    {
     "port":80
    }
   ],
   "selector":{
     "name":"frontend"
   }
  }
}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。