kubernetes云平台管理实战：k8s附加组件DNS服务（十三）

一、为什么需要DNS组件

进入容器

[root@master ~]# kubectl exec -it myweb-7vjgt sh
root@myweb-7vjgt:/usr/local/tomcat# 

查看环境变量

root@myweb-7vjgt:/usr/local/tomcat# env
MYWEB_PORT_8080_TCP_PORT=8080
HOSTNAME=myweb-7vjgt
TOMCAT_VERSION=8.0.35
KUBERNETES_PORT_443_TCP_PORT=443
TERM=xterm
KUBERNETES_PORT=tcp://10.254.0.1:443
CATALINA_HOME=/usr/local/tomcat
MYWEB_PORT_8080_TCP_ADDR=10.254.202.136
MYWEB_PORT_8080_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_HOST=10.254.0.1
MYWEB_SERVICE_HOST=10.254.202.136
MYSQL_PORT_3306_TCP_PORT=3306
MYSQL_PORT_3306_TCP=tcp://10.254.168.177:3306
PATH=/usr/local/tomcat/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MYWEB_PORT_8080_TCP=tcp://10.254.202.136:8080
PWD=/usr/local/tomcat
JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64/jre
MYWEB_SERVICE_PORT=8080
LANG=C.UTF-8
JAVA_VERSION=7u101
SHLVL=1
JAVA_DEBIAN_VERSION=7u101-2.6.6-1~deb8u1
HOME=/root
TOMCAT_MAJOR=8
KUBERNETES_PORT_443_TCP_PROTO=tcp
OPENSSL_VERSION=1.0.2h-1
KUBERNETES_SERVICE_PORT_HTTPS=443
MYSQL_PORT_3306_TCP_PROTO=tcp
MYSQL_PORT_3306_TCP_ADDR=10.254.168.177
MYSQL_SERVICE_PORT=3306
TOMCAT_TGZ_URL=https://www.apache.org/dist/tomcat/tomcat-8/v8.0.35/bin/apache-tomcat-8.0.35.tar.gz
KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1
KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443
MYSQL_PORT=tcp://10.254.168.177:3306
MYWEB_PORT=tcp://10.254.202.136:8080
MYSQL_SERVICE_HOST=10.254.168.177
_=/usr/bin/env
root@myweb-7vjgt:/usr/local/tomcat# env|grep -iE 'kubernetes|mysql|myweb|wc -l'
MYWEB_PORT_8080_TCP_PORT=8080
HOSTNAME=myweb-7vjgt
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT=tcp://10.254.0.1:443
MYWEB_PORT_8080_TCP_ADDR=10.254.202.136
MYWEB_PORT_8080_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_HOST=10.254.0.1
MYWEB_SERVICE_HOST=10.254.202.136
MYSQL_PORT_3306_TCP_PORT=3306
MYSQL_PORT_3306_TCP=tcp://10.254.168.177:3306
MYWEB_PORT_8080_TCP=tcp://10.254.202.136:8080
MYWEB_SERVICE_PORT=8080
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT_HTTPS=443
MYSQL_PORT_3306_TCP_PROTO=tcp
MYSQL_PORT_3306_TCP_ADDR=10.254.168.177
MYSQL_SERVICE_PORT=3306
KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1
KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443
MYSQL_PORT=tcp://10.254.168.177:3306
MYWEB_PORT=tcp://10.254.202.136:8080
MYSQL_SERVICE_HOST=10.254.168.177
root@myweb-7vjgt:/usr/local/tomcat# env|grep -iE 'kubernetes|mysql|myweb|wc -l'
MYWEB_PORT_8080_TCP_PORT=8080
HOSTNAME=myweb-7vjgt
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT=tcp://10.254.0.1:443
MYWEB_PORT_8080_TCP_ADDR=10.254.202.136
MYWEB_PORT_8080_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_HOST=10.254.0.1
MYWEB_SERVICE_HOST=10.254.202.136
MYSQL_PORT_3306_TCP_PORT=3306
MYSQL_PORT_3306_TCP=tcp://10.254.168.177:3306
MYWEB_PORT_8080_TCP=tcp://10.254.202.136:8080
MYWEB_SERVICE_PORT=8080
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT_HTTPS=443
MYSQL_PORT_3306_TCP_PROTO=tcp
MYSQL_PORT_3306_TCP_ADDR=10.254.168.177
MYSQL_SERVICE_PORT=3306
KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1
KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443
MYSQL_PORT=tcp://10.254.168.177:3306
MYWEB_PORT=tcp://10.254.202.136:8080
MYSQL_SERVICE_HOST=10.254.168.177

环境变量数量统计

root@myweb-7vjgt:/usr/local/tomcat# env|grep -iE 'kubernetes|mysql|myweb' |wc -l
23

Kubernetes中有一个很重要的特性，服务自发现。一旦一个service被创建，该service的service IP和service port等信息都可以被注入到pod中供它们使用。
Kubernetes主要支持两种service发现，机制：环境变量和DNS。

没有dns服务的时候，kubernetes会采用环境变量的形式，一旦有很多个service，环境变量会变得很复杂，为了解决这个问题，我们使用DNS服务。

二、实验准备

1、文件结构与组成

[root@master skydns]# ll
total 16
-rw-r--r-- 1 root root 5696 May 13 10:26 skydns-rc.yaml
-rw-r--r-- 1 root root 1135 Feb  5  2018 skydns-svc.yaml
-rw-r--r-- 1 root root  243 Jun 25  2019 test_dns_pod.yaml

2、具体内容

skydns-rc.yaml

[root@master skydns]# cat skydns-rc.yaml
# Copyright 2016 The Kubernetes Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# TODO - At some point, we need to rename all skydns-*.yaml.* files to kubedns-*.yaml.*
# Should keep target in cluster/addons/dns-horizontal-autoscaler/dns-horizontal-autoscaler.yaml
# in sync with this file.

# __MACHINE_GENERATED_WARNING__

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
spec:
  replicas: 1
  # replicas: not specified here:
  # 1. In order to make Addon Manager do not reconcile this replicas parameter.
  # 2. Default is 1.
  # 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on.
  strategy:
    rollingUpdate:
      maxSurge: 10%
      maxUnavailable: 0
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
      annotations:
        scheduler.alpha.kubernetes.io/critical-pod: ''
        scheduler.alpha.kubernetes.io/tolerations: '[{"key":"CriticalAddonsOnly", "operator":"Exists"}]'
    spec:
      containers:
      - name: kubedns
        image: myhub.fdccloud.com/library/kubedns-amd64:1.9
        resources:
          # TODO: Set memory limits when we've profiled the container for large
          # clusters, then set request = limit to keep this container in
          # guaranteed class. Currently, this container falls into the
          # "burstable" category so the kubelet doesn't backoff from restarting it.
          limits:
            memory: 170Mi
          requests:
            cpu: 100m
            memory: 70Mi
        livenessProbe:
          httpGet:
            path: /healthz-kubedns
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        readinessProbe:
          httpGet:
            path: /readiness
            port: 8081
            scheme: HTTP
          # we poll on pod startup for the Kubernetes master service and
          # only setup the /readiness HTTP server once that's available.
          initialDelaySeconds: 3
          timeoutSeconds: 5
        args:
        - --domain=cluster.local.
        - --dns-port=10053
        - --config-map=kube-dns
        - --kube-master-url=http://192.168.118.18:8080
        # This should be set to v=2 only after the new image (cut from 1.5) has
        # been released, otherwise we will flood the logs.
        - --v=0
        #__PILLAR__FEDERATIONS__DOMAIN__MAP__
        env:
        - name: PROMETHEUS_PORT
          value: "10055"
        ports:
        - containerPort: 10053
          name: dns-local
          protocol: UDP
        - containerPort: 10053
          name: dns-tcp-local
          protocol: TCP
        - containerPort: 10055
          name: metrics
          protocol: TCP
      - name: dnsmasq
        image: myhub.fdccloud.com/library/kube-dnsmasq-amd64:1.4
        livenessProbe:
          httpGet:
            path: /healthz-dnsmasq
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        args:
        - --cache-size=1000
        - --no-resolv
        - --server=127.0.0.1#10053
        #- --log-facility=-
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
        # see: https://github.com/kubernetes/kubernetes/issues/29055 for details
        resources:
          requests:
            cpu: 150m
            memory: 10Mi
      - name: dnsmasq-metrics
        image: myhub.fdccloud.com/library/dnsmasq-metrics-amd64:1.0
        livenessProbe:
          httpGet:
            path: /metrics
            port: 10054
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        args:
        - --v=2
        - --logtostderr
        ports:
        - containerPort: 10054
          name: metrics
          protocol: TCP
        resources:
          requests:
            memory: 10Mi
      - name: healthz
        image: myhub.fdccloud.com/library/exechealthz-amd64:1.2
        resources:
          limits:
            memory: 50Mi
          requests:
            cpu: 10m
            # Note that this container shouldn't really need 50Mi of memory. The
            # limits are set higher than expected pending investigation on #29688.
            # The extra memory was stolen from the kubedns container to keep the
            # net memory requested by the pod constant.
            memory: 50Mi
        args:
        - --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
        - --url=/healthz-dnsmasq
        - --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1:10053 >/dev/null
        - --url=/healthz-kubedns
        - --port=8080
        - --quiet
        ports:
        - containerPort: 8080
          protocol: TCP
      dnsPolicy: Default  # Don't use cluster DNS.

skydns-svc.yaml

[root@master skydns]# cat skydns-svc.yaml
# Copyright 2016 The Kubernetes Authors.
......
# TODO - At some point, we need to rename all skydns-*.yaml.* files to kubedns-*.yaml.*
# Warning: This is a file generated from the base underscore template file: skydns-svc.yaml.base

apiVersion: v1
kind: Service
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    kubernetes.io/name: "KubeDNS"
spec:
  selector:
    k8s-app: kube-dns
  clusterIP: 10.254.230.254
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

test_dns_pod.yaml

[root@master skydns]# cat test_dns_pod.yaml
apiVersion: v1
kind: Pod
metadata:
  labels:
    name: busybox
    role: master
  name: busybox2
spec:
  containers:
  - name: busybox
    image: docker.io/busybox:latest
    imagePullPolicy: IfNotPresent
    command:
    - sleep
    - "3600"

三、操作演示过程

1、安装部署sky-dns

[root@master pod]# cd skydns
[root@master skydns]# ll
total 16
-rw-r--r-- 1 root root 5691 Jun 25  2019 skydns-rc.yaml
-rw-r--r-- 1 root root 1135 Feb  5  2018 skydns-svc.yaml
-rw-r--r-- 1 root root  243 Jun 25  2019 test_dns_pod.yaml
[root@master skydns]# vim skydns-rc.yaml 
[root@master skydns]# kubectl create -f skydns-rc.yaml
deployment "kube-dns" created
[root@master skydns]# kubectl create -f skydns-svc.yaml
service "kube-dns" created
[root@master skydns]# kubectl get pod --namespace=kube-system 
NAME                        READY     STATUS    RESTARTS   AGE
kube-dns-1835838994-jm5bk   4/4       Running   0          1m

2、修改kubelet配置

修改各node节点上的/etc/kubernetes/kubelet配置文件，增加如下行：

KUBELET_ARGS="--cluster_dns=10.254.230.254 --cluster_domain=cluster.local"

重启各node节点kubelet：

systemctl restart kubelet

四、测试代码及截图

创建测试pod

[root@master skydns]# kubectl create -f test_dns_pod.yaml
pod "busybox2" created

进入测试pod

[root@master skydns]# kubectl exec -it busybox2 sh

域名解析测试

/ # nslookup kubernetes
Server:	10.254.230.254
Address:	10.254.230.254:53

Non-authoritative answer:
Name:	kubernetes.default.svc.cluster.local
Address: 10.254.0.1

*** Can't find kubernetes.svc.cluster.local: No answer
*** Can't find kubernetes.cluster.local: No answer
*** Can't find kubernetes.localdomain: No answer
*** Can't find kubernetes.default.svc.cluster.local: No answer
*** Can't find kubernetes.svc.cluster.local: No answer
*** Can't find kubernetes.cluster.local: No answer
*** Can't find kubernetes.localdomain: No answer