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Kubernetes（简称为K8S）是目前流行的容器编排平台之一，提供了便捷的容器管理和部署功能。在K8S中，Pod是最基础的工作单元，可由一个或多个容器组成。每个Pod都会被分配一个唯一的IP地址，以便在集群内部进行服务发现和网络通信。本文将详细介绍K8S中Pod IP的分配方法，并提供代码示例帮助读者理解和实践。
在Kubernetes中，Pod IP的分配过程包含以下几个步骤：
步骤 | 描述 |
1. 为节点分配CIDR范围 | 配置网络插件，为每个节点分配一个CIDR范围 |
2. 为Pod分配IP地址 | 控制平面根据节点的CIDR范围为Pod分配一个可用的IP地址 |
3. 给Pod分配IP地址 | 使用网络插件为Pod分配并配置IP地址 |
下面我们来具体的解释每个步骤需要做什么，并提供相应的代码示例：
步骤1. 为节点分配CIDR范围 在K8S集群中，每个节点都需要一个CIDR（无类型域间选路前缀）范围来分配给Pod。可以通过编辑kubelet的配置文件来指定CIDR范围，示例代码如下：
vi /etc/kubernetes/kubelet.conf修改配置文件kubelet.conf中的参数--pod-cidr，配置每个节点的CIDR范围。
步骤2. 为Pod分配IP地址 在Pod被创建时，Kubernetes控制平面会为其分配一个可用的IP地址。这个过程是由kube-controller-manager组件完成的，无需开发者手动操作。
步骤3. 给Pod分配IP地址 在Pod被创建的同时，相关的网络插件也会为其分配和配置IP地址。目前Kubernetes支持多种网络插件，如Flannel、Calico等。以下是Flannel网络插件的示例代码，供参考：
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/main/Documentation/kube-flannel.yml这条命令将通过kubectl工具应用kube-flannel.yml配置文件来部署Flannel网络插件。Flannel会为每个Node创建一个虚拟网络，并为Pod分配IP地址。
至此，Kubernetes中Pod IP的分配过程已经完成。
结论： 本文详细介绍了Kubernetes中Pod IP的分配方法，并提供了相关的代码示例和注释。开发者可以按照步骤进行操作，通过配置节点CIDR范围、使用kube-controller-manager自动分配IP和应用网络插件为Pod分配IP地址，来达到分配Pod IP地址的目的。通过本文的指导，相信开发者可以快速上手并成功实现该功能。
附录 - Flannel网络插件配置文件kube-flannel.yml示例：
---
apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
name: psp.flannel.unprivileged
annotations:
seccomp.security.alpha.kubernetes.io/allowedProfileNames: docker/default
seccomp.security.alpha.kubernetes.io/defaultProfileName: docker/default
apparmor.security.beta.kubernetes.io/allowedProfileNames: runtime/default
apparmor.security.beta.kubernetes.io/defaultProfileName: runtime/default
spec:
privileged: false
volumes:
- configMap
- secret
- emptyDir
- hostPath
allowedHostPaths:
- pathPrefix: "/etc/cni/net.d"
- pathPrefix: "/etc/kube-flannel"
- pathPrefix: "/run/flannel"
readOnlyRootFilesystem: false
# Users and groups
runAsUser:
rule: RunAsAny
supplementalGroups:
rule: RunAsAny
fsGroup:
rule: RunAsAny
# Privilege Escalation
allowPrivilegeEscalation: false
defaultAllowPrivilegeEscalation: false
# Capabilities
allowedCapabilities: ['NET_ADMIN', 'NET_RAW']
defaultAddCapabilities: []
requiredDropCapabilities: []
# Host namespaces
hostPID: false
hostIPC: false
hostNetwork: true
hostPorts:
- min: 0
max: 65535
# SELinux
seLinux:
# SELinux is unused in CaaSP
rule: 'RunAsAny'
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: flannel
rules:
- apiGroups: ['extensions']
resources: ['podsecuritypolicies']
verbs: ['use']
resourceNames: ['psp.flannel.unprivileged']
- apiGroups:
- ""
resources:
- pods
verbs:
- get
- apiGroups:
- ""
resources:
- nodes
verbs:
- list
- watch
- apiGroups:
- ""
resources:
- nodes/status
verbs:
- patch
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
name: flannel
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: flannel
subjects:
- kind: ServiceAccount
name: flannel
namespace: kube-system
---
apiVersion: v1
kind: ServiceAccount
metadata:
name: flannel
namespace: kube-system
---
kind: ConfigMap
apiVersion: v1
metadata:
name: kube-flannel-cfg
namespace: kube-system
labels:
tier: node
app: flannel
data:
cni-conf.json: |
{
"name": "cbr0",
"cniVersion": "0.3.1",
"plugins": [
{
"type": "flannel",
"delegate": {
"hairpinMode": true,
"isDefaultGateway": true
}
},
{
"type": "portmap",
"capabilities": {
"portMappings": true
}
}
]
}
net-conf.json: |
{
"Network": "10.244.0.0/16",
"Backend": {
"Type": "vxlan"
}
}
---
apiVersion: apps/v1
kind: DaemonSet
metadata:
name: kube-flannel-ds
namespace: kube-system
labels:
tier: node
app: flannel
spec:
selector:
matchLabels:
app: flannel
template:
metadata:
labels:
tier: node
app: flannel
spec:
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/os
operator: In
values:
- linux
hostNetwork: true
priorityClassName: system-node-critical
tolerations:
- operator: Exists
effect: NoSchedule
serviceAccountName: flannel
initContainers:
- name: install-cni
image: quay.io/coreos/flannel:v0.13.1-rc1
command:
- cp
args:
- -f
- /etc/kube-flannel/cni-conf.json
- /etc/cni/net.d/10-flannel.conflist
volumeMounts:
- name: cni
mountPath: /etc/cni/net.d
- name: flannel-cfg
mountPath: /etc/kube-flannel/
containers:
- name: kube-flannel
image: quay.io/coreos/flannel:v0.13.1-rc1
command:
- /opt/bin/flanneld
args:
- --ip-masq
- --kube-subnet-mgr
resources:
requests:
cpu: "100m"
memory: "50Mi"
limits:
cpu: "100m"
memory: "50Mi"
securityContext:
privileged: false
capabilities:
add: ["NET_ADMIN", "NET_RAW"]
env:
- name: POD_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
- name: POD_NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
volumeMounts:
- name: run
mountPath: /run/flannel
- name: flannel-cfg
mountPath: /etc/kube-flannel/
volumes:
- name: run
hostPath:
path: /run/flannel
- name: cni
hostPath:
path: /etc/cni/net.d
- name: flannel-cfg
configMap:
name: kube-flannel-cfg
