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
23Kubernetes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.yaml2、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: TCPtest_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 1m2、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来源：oschina
链接：https://my.oschina.net/u/4408441/blog/4287829