Kubernetes的service资源介绍

service 

  三种工作模式：userspace、iptables、ipvs 

删除手动创建的service

[root@master ~]# kubectl delete svc redis
service "redis" deleted
[root@master ~]# kubectl get svc
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes   ClusterIP   10.96.0.1        <none>        443/TCP        17d
myapp        NodePort    10.103.191.244   <none>        80:31339/TCP   17d
nginx        ClusterIP   10.108.177.175   <none>        80/TCP         17d

定义service 的顶级资源清单帮助

[root@master ~]# kubectl explain svc
KIND:     Service
VERSION:  v1

DESCRIPTION:
     Service is a named abstraction of software service (for example, mysql)
     consisting of local port (for example 3306) that the proxy listens on, and
     the selector that determines which pods will answer requests sent through
     the proxy.

FIELDS:
   apiVersion	<string>  版本
     APIVersion defines the versioned schema of this representation of an
     object. Servers should convert recognized schemas to the latest internal
     value, and may reject unrecognized values. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#resources

   kind	<string>  类型
     Kind is a string value representing the REST resource this object
     represents. Servers may infer this from the endpoint the client submits
     requests to. Cannot be updated. In CamelCase. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#types-kinds

   metadata	<Object>  元数据
     Standard object's metadata. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata

   spec	<Object>  期望状态
     Spec defines the behavior of a service.
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status

   status	<Object>
     Most recently observed status of the service. Populated by the system.
     Read-only. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status

　　spec 的重要字段介绍

[root@master ~]# kubectl explain svc.spec
KIND:     Service
VERSION:  v1

RESOURCE: spec <Object>

DESCRIPTION:
     Spec defines the behavior of a service.
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status

     ServiceSpec describes the attributes that a user creates on a service.

FIELDS:
   clusterIP	<string>  集群的podIP，动态分配的，如果想要固定地址可以使用这个字段定义
     clusterIP is the IP address of the service and is usually assigned randomly
     by the master. If an address is specified manually and is not in use by
     others, it will be allocated to the service; otherwise, creation of the
     service will fail. This field can not be changed through updates. Valid
     values are "None", empty string (""), or a valid IP address. "None" can be
     specified for headless services when proxying is not required. Only applies
     to types ClusterIP, NodePort, and LoadBalancer. Ignored if type is
     ExternalName. More info:
     https://kubernetes.io/docs/concepts/services-networking/service/#virtual-ips-and-service-proxies

   externalIPs	<[]string>
     externalIPs is a list of IP addresses for which nodes in the cluster will
     also accept traffic for this service. These IPs are not managed by
     Kubernetes. The user is responsible for ensuring that traffic arrives at a
     node with this IP. A common example is external load-balancers that are not
     part of the Kubernetes system.

   externalName	<string>
     externalName is the external reference that kubedns or equivalent will
     return as a CNAME record for this service. No proxying will be involved.
     Must be a valid RFC-1123 hostname (https://tools.ietf.org/html/rfc1123) and
     requires Type to be ExternalName.

   externalTrafficPolicy	<string>
     externalTrafficPolicy denotes if this Service desires to route external
     traffic to node-local or cluster-wide endpoints. "Local" preserves the
     client source IP and avoids a second hop for LoadBalancer and Nodeport type
     services, but risks potentially imbalanced traffic spreading. "Cluster"
     obscures the client source IP and may cause a second hop to another node,
     but should have good overall load-spreading.

   healthCheckNodePort	<integer>
     healthCheckNodePort specifies the healthcheck nodePort for the service. If
     not specified, HealthCheckNodePort is created by the service api backend
     with the allocated nodePort. Will use user-specified nodePort value if
     specified by the client. Only effects when Type is set to LoadBalancer and
     ExternalTrafficPolicy is set to Local.

   loadBalancerIP	<string>
     Only applies to Service Type: LoadBalancer LoadBalancer will get created
     with the IP specified in this field. This feature depends on whether the
     underlying cloud-provider supports specifying the loadBalancerIP when a
     load balancer is created. This field will be ignored if the cloud-provider
     does not support the feature.

   loadBalancerSourceRanges	<[]string>
     If specified and supported by the platform, this will restrict traffic
     through the cloud-provider load-balancer will be restricted to the
     specified client IPs. This field will be ignored if the cloud-provider does
     not support the feature." More info:
     https://kubernetes.io/docs/tasks/access-application-cluster/configure-cloud-provider-firewall/

   ports	<[]Object>  端口与容器端口建立关系的定义
     The list of ports that are exposed by this service. More info:
     https://kubernetes.io/docs/concepts/services-networking/service/#virtual-ips-and-service-proxies

   publishNotReadyAddresses	<boolean>
     publishNotReadyAddresses, when set to true, indicates that DNS
     implementations must publish the notReadyAddresses of subsets for the
     Endpoints associated with the Service. The default value is false. The
     primary use case for setting this field is to use a StatefulSet's Headless
     Service to propagate SRV records for its Pods without respect to their
     readiness for purpose of peer discovery.

   selector	<map[string]string>  关联到那些pod资源上
     Route service traffic to pods with label keys and values matching this
     selector. If empty or not present, the service is assumed to have an
     external process managing its endpoints, which Kubernetes will not modify.
     Only applies to types ClusterIP, NodePort, and LoadBalancer. Ignored if
     type is ExternalName. More info:
     https://kubernetes.io/docs/concepts/services-networking/service/

   sessionAffinity	<string>  会话粘性
     Supports "ClientIP" and "None". Used to maintain session affinity. Enable
     client IP based session affinity. Must be ClientIP or None. Defaults to
     None. More info:
     https://kubernetes.io/docs/concepts/services -networking/service/#virtual-ips-and-service-proxies

   sessionAffinityConfig	<Object>
     sessionAffinityConfig contains the configurations of session affinity.

   type	<string>  指定type ，ClusterIP集群内部的通信地址NodePort  节点的地址供外部访问  LoadBalancer：公有云的负载均衡器  ExternalName：集群外部服务引入到集群内部使用
     type determines how the Service is exposed. Defaults to ClusterIP. Valid
     options are ExternalName, ClusterIP, ,NodePort and LoadBalancer.
     "ExternalName" maps to the specified externalName. "ClusterIP" allocates a
     cluster-internal IP address for load-balancing to endpoints. Endpoints are
     determined by the selector or if that is not specified, by manual
     construction of an Endpoints object. If clusterIP is "None", no virtual IP
     is allocated and the endpoints are published as a set of endpoints rather
     than a stable IP. "NodePort" builds on ClusterIP and allocates a port on
     every node which routes to the clusterIP. "LoadBalancer" builds on NodePort
     and creates an external load-balancer (if supported in the current cloud)
     which routes to the clusterIP. More info:
     https://kubernetes.io/docs/concepts/services-networking/service/#publishing-services-service-types

　　ports 字段的定义

[root@master ~]# kubectl explain svc.spec.ports
KIND:     Service
VERSION:  v1

RESOURCE: ports <[]Object>

DESCRIPTION:
     The list of ports that are exposed by this service. More info:
     https://kubernetes.io/docs/concepts/services-networking/service/#virtual-ips-and-service-proxies

     ServicePort contains information on service's port.

FIELDS:
   name	<string>  名字
     The name of this port within the service. This must be a DNS_LABEL. All
     ports within a ServiceSpec must have unique names. This maps to the 'Name'
     field in EndpointPort objects. Optional if only one ServicePort is defined
     on this service.

   nodePort	<integer>  节点的端口
     The port on each node on which this service is exposed when type=NodePort
     or LoadBalancer. Usually assigned by the system. If specified, it will be
     allocated to the service if unused or else creation of the service will
     fail. Default is to auto-allocate a port if the ServiceType of this Service
     requires one. More info:
     https://kubernetes.io/docs/concepts/services-networking/service/#type-nodeport

   port	<integer> -required-  对外部提供访问服务的端口
     The port that will be exposed by this service.

   protocol	<string>  协议
     The IP protocol for this port. Supports "TCP", "UDP", and "SCTP". Default
     is TCP.

   targetPort	<string>  容器的端口
     Number or name of the port to access on the pods targeted by the service.
     Number must be in the range 1 to 65535. Name must be an IANA_SVC_NAME. If
     this is a string, it will be looked up as a named port in the target Pod's
     container ports. If this is not specified, the value of the 'port' field is
     used (an identity map). This field is ignored for services with
     clusterIP=None, and should be omitted or set equal to the 'port' field.
     More info:
     https://kubernetes.io/docs/concepts/services-networking/service/#defining-a-service

　　service 的yml 文件定义

[root@master manifests]# cat redis-svc.yaml 
apiVersion: v1
kind: Service
metadata:
  name: redis-svc
  namespace: default
spec:
  selector:
    app: redis   绑定的pod资源根据标签绑定的
  clusterIP: 10.97.97.97    提供集群内访问地址
  type: ClusterIP  类型
  ports:
  - port: 6379  service 对外提供的服务端口
    targetPort: 6379   容器里暴露的端口

　　创建这个service服务

[root@master manifests]# kubectl apply -f redis-svc.yaml 
service/redis-svc created

　　查看这个service的运行状态

[root@master manifests]# kubectl describe svc redis-svc
Name:              redis-svc
Namespace:         default
Labels:            <none>
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"redis-svc","namespace":"default"},"spec":{"clusterIP":"10.97.97.9...
Selector:          app=redis
Type:              ClusterIP
IP:                10.97.97.97
Port:              <unset>  6379/TCP
TargetPort:        6379/TCP
Endpoints:         10.244.1.67:6379
Session Affinity:  None
Events:            <none>

　　DNS资源记录格式

SVC_NAME.NS_NAME.DOMAIN.LTD
服务名.名称空间.资源域名后缀
默认资源后缀：svc.cluster.local 

　　定一个节点级别的服务

[root@master manifests]# cat myapp-svc.yaml 
apiVersion: v1
kind: Service
metadata:
  name: myapp
  namespace: default
spec:
  selector:
    cx: yl  绑定的pod
  clusterIP: 10.99.99.99  集群内部的地址
  type: NodePort
  ports:
  - port: 80  集群内部访问端口
    targetPort: 80  容器里暴露的端口
    nodePort: 30080  外部访问端口

　　查看各个节点的端口

[root@master ~]# ss -lntp | grep 30080  主节点
LISTEN     0      128         :::30080                   :::*                   users:(("kube-proxy",pid=15320,fd=11))
[root@node01 ~]# ss -lntp | grep 30080   node01节点
LISTEN     0      128         :::30080                   :::*                   users:(("kube-proxy",pid=10352,fd=11))
[root@node02 ~]# ss -lntp | grep 30080   node02 节点
LISTEN     0      128         :::30080                   :::*                   users:(("kube-proxy",pid=10422,fd=11))

　　通过打补丁方式修改回话粘性

[root@master manifests]# kubectl patch svc myapp -p '{"spec":{"sessionAffinity":"ClientIP"}}'
service/myapp patched
[root@master manifests]# kubectl describe svc myapp
Name:                     myapp
Namespace:                default
Labels:                   <none>
Annotations:              kubectl.kubernetes.io/last-applied-configuration:
                            {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"myapp","namespace":"default"},"spec":{"clusterIP":"10.99.99.99","...
Selector:                 cx=yl
Type:                     NodePort
IP:                       10.99.99.99
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
NodePort:                 <unset>  30080/TCP
Endpoints:                10.244.1.60:80,10.244.1.61:80,10.244.1.64:80 + 2 more...
Session Affinity:         ClientIP
External Traffic Policy:  Cluster
Events:                   <none>