Kubernetes（k8s）安装dns附件组件以及使用
1、K8s附加组件DNS服务。
答：Kubernetes中有一个很重要的特性，服务子发现。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，第一种是环境变量，第二种是DNS。没有dns服务的时候，kubernetes会采用环境变量的形式，一个有很多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。
2、Pod的环境变量如何查看呢？
[ ~]# kubectl get all -o wide NAME DESIRED CURRENT READY AGE CONTAINER(S) IMAGE(S) SELECTOR rc/mysql 1 1 1 16h mysql 192.168.110.133:5000/mysql:5.7.30 app=mysql rc/myweb 1 1 1 1h myweb 192.168.110.133:5000/tomcat:latest app=myweb NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR svc/kubernetes 10.254.0.1 <none> 443/TCP 13d <none> svc/mysql 10.254.245.194 <none> 3306/TCP 16h app=mysql svc/myweb 10.254.222.197 <nodes> 8080:30008/TCP 1h app=myweb NAME READY STATUS RESTARTS AGE IP NODE po/mysql-537xf 1/1 Running 1 16h 172.16.16.3 k8s-master po/myweb-8b7n3 1/1 Running 0 1h 172.16.32.3 k8s-node3 [ ~]# kubectl exec -it myweb-8b7n3 /bin/bas base64 basename bash bashbug bashbug-64 [ ~]# kubectl exec -it myweb-8b7n3 /bin/bas base64 basename bash bashbug bashbug-64 [ ~]# kubectl exec -it myweb-8b7n3 /bin/bash :/usr/local/tomcat# env KUBERNETES_SERVICE_PORT_HTTPS=443 MYSQL_PORT=tcp://10.254.245.194:3306 MYSQL_PORT_3306_TCP_ADDR=10.254.245.194 KUBERNETES_SERVICE_PORT=443 MYSQL_PORT_3306_TCP_PORT=3306 HOSTNAME=myweb-8b7n3 JAVA_HOME=/usr/local/openjdk-11 GPG_KEYS=05AB33110949707C93A279E3D3EFE6B686867BA6 07E48665A34DCAFAE522E5E6266191C37C037D42 47309207D818FFD8DCD3F83F1931D684307A10A5 541FBE7D8F78B25E055DDEE13C370389288584E7 61B832AC2F1C5A90F0F9B00A1C506407564C17A3 79F7026C690BAA50B92CD8B66A3AD3F4F22C4FED 9BA44C2621385CB966EBA586F72C284D731FABEE A27677289986DB50844682F8ACB77FC2E86E29AC A9C5DF4D22E99998D9875A5110C01C5A2F6059E7 DCFD35E0BF8CA7344752DE8B6FB21E8933C60243 F3A04C595DB5B6A5F1ECA43E3B7BBB100D811BBE F7DA48BB64BCB84ECBA7EE6935CD23C10D498E23 JAVA_BASE_URL=https://github.com/AdoptOpenJDK/openjdk11-upstream-binaries/releases/download/jdk-11.0.7%2B10/OpenJDK11U-jdk_ MYSQL_PORT_3306_TCP=tcp://10.254.245.194:3306 PWD=/usr/local/tomcat JAVA_URL_VERSION=11.0.7_10 TOMCAT_SHA512=75e16a00e02782961a7753dc9afaf6d209afa5f22d320319778fd0ee5e3b47009da522ac735599f1739bff6e809c2da9081dbbd4b8de54a82cf5b8cfbd8030ff TOMCAT_MAJOR=9 HOME=/root LANG=C.UTF-8 KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443 TOMCAT_NATIVE_LIBDIR=/usr/local/tomcat/native-jni-lib TERM=xterm MYSQL_SERVICE_PORT=3306 CATALINA_HOME=/usr/local/tomcat MYSQL_SERVICE_HOST=10.254.245.194 MYSQL_PORT_3306_TCP_PROTO=tcp SHLVL=1 KUBERNETES_PORT_443_TCP_PROTO=tcp KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1 LD_LIBRARY_PATH=/usr/local/tomcat/native-jni-lib KUBERNETES_SERVICE_HOST=10.254.0.1 KUBERNETES_PORT=tcp://10.254.0.1:443 KUBERNETES_PORT_443_TCP_PORT=443 PATH=/usr/local/tomcat/bin:/usr/local/openjdk-11/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin TOMCAT_VERSION=9.0.36 JAVA_VERSION=11.0.7 _=/usr/bin/env :/usr/local/tomcat# java -version openjdk version "11.0.7" 2020-04-14 OpenJDK Runtime Environment 18.9 (build 11.0.7+10) OpenJDK 64-Bit Server VM 18.9 (build 11.0.7+10, mixed mode) :/usr/local/tomcat#
如果有几个Service就会有几个环境变量，这里进行简单的过滤。
:/usr/local/tomcat# env | grep -iE ‘kubernetes|mysql|myweb‘ KUBERNETES_SERVICE_PORT_HTTPS=443 MYSQL_PORT=tcp://10.254.207.238:3306 MYSQL_PORT_3306_TCP_ADDR=10.254.207.238 KUBERNETES_SERVICE_PORT=443 MYSQL_PORT_3306_TCP_PORT=3306 HOSTNAME=myweb-hsdwn MYSQL_PORT_3306_TCP=tcp://10.254.207.238:3306 KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443 MYSQL_SERVICE_PORT=3306 MYSQL_SERVICE_HOST=10.254.207.238 MYSQL_PORT_3306_TCP_PROTO=tcp KUBERNETES_PORT_443_TCP_PROTO=tcp KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1 KUBERNETES_SERVICE_HOST=10.254.0.1 KUBERNETES_PORT=tcp://10.254.0.1:443 KUBERNETES_PORT_443_TCP_PORT=443 :/usr/local/tomcat#
1 :/usr/local/tomcat# env | grep -iE ‘kubernetes|mysql|myweb‘ | wc -l 2 16 3 :/usr/local/tomcat#
如果环境变量过多的话，会变得很复杂，所以引入了DNS服务。
3、下载DNS的资料包，如下所示：
[ tomcat_demo]# wget https://www.qstack.com.cn/skydns.zip --2020-06-18 15:31:25-- https://www.qstack.com.cn/skydns.zip Resolving www.qstack.com.cn (www.qstack.com.cn)... 123.125.46.149, 111.202.85.37 Connecting to www.qstack.com.cn (www.qstack.com.cn)|123.125.46.149|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 3411 (3.3K) [application/zip] Saving to: ‘skydns.zip’ 100%[======================================================================================>] 3,411 --.-K/s in 0s 2020-06-18 15:31:26 (40.5 MB/s) - ‘skydns.zip’ saved [3411/3411] [master tomcat_demo]# ls mysql-rc.yml mysql-svc.yml skydns.zip tomcat-rc.yml tomcat-svc.yml [master tomcat_demo]# cd .. [ k8s]# mv tomcat_demo/skydns.zip . [master k8s]# ls book-master.war deploy pod rc skydns.zip svc tomcat_demo tomcat_demo.zip [master k8s]# unzip skydns.zip Archive: skydns.zip creating: skydns/ inflating: skydns/skydns-rc.yaml inflating: skydns/skydns-svc.yaml inflating: skydns/test_dns_pod.yaml [master k8s]# ls book-master.war deploy pod rc skydns skydns.zip svc tomcat_demo tomcat_demo.zip [ k8s]#
修改skydns-rc.yaml配置文件。
# 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://10.0.0.11:8080
# 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.需要将此地址的ip地址修改为自己api-server的地址。
开始创建RC，创建需要很长时间的。
1 [ skydns]# kubectl create -f skydns-rc.yaml 2 deployment "kube-dns" created 3 [ skydns]#
开始创建SVC，修改配置文件，使用kubectl get svc查看CLUSTER-IP的地址，只要未被使用，就可以配置到skydns-svc.yaml 配置文件中即可。
[ ~]# kubectl get svc NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes 10.254.0.1 <none> 443/TCP 13d mysql 10.254.207.238 <none> 3306/TCP 42m myweb 10.254.29.22 <nodes> 8080:30008/TCP 28m [ ~]#
创建svc的命令，如下所示：
[ skydns]# vim skydns-svc.yaml [ skydns]# kubectl create -f skydns-svc.yaml service "kube-dns" created [ skydns]#
根据命名空间来查看创建好的pod，可以看到这个Pod里面的四个容器都已经运行起来了。
[ skydns]# kubectl get pod --namespace=kube-system NAME READY STATUS RESTARTS AGE kube-dns-778415672-f9ssw 4/4 Running 0 6m [ skydns]#
[ skydns]# kubectl get all --namespace=kube-system NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE deploy/kube-dns 1 1 1 1 7m NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE svc/kube-dns 10.254.230.254 <none> 53/UDP,53/TCP 3m NAME DESIRED CURRENT READY AGE rs/kube-dns-778415672 1 1 1 7m NAME READY STATUS RESTARTS AGE po/kube-dns-778415672-f9ssw 4/4 Running 0 7m [ skydns]#
如果希望所有的Pod都使用DNS的话，还需要修改一下配置文件。修改kubelet配置，修改各个node节点上的/etc/kubernetes/kubelet配置文件，增加如下行。然后再重启各个node节点的kubelet。
4、修改kubelet配置，修改各个node节点上的/etc/kubernetes/kubelet配置文件，增加如下行。然后再重启各个node节点的kubelet。
1 KUBELET_ARGS="--cluster_dns=10.254.230.254 --cluster_domain=cluster.local"
这个地址就是刚才自己配置的svc的地址，可以使用命令进行查看。
[ skydns]# vim /etc/kubernetes/kubelet [ skydns]# kubectl get svc --namespace=kube-system NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE kube-dns 10.254.230.254 <none> 53/UDP,53/TCP 9m [ skydns]#
然后重启三台Node节点的kubelet服务。
[master skydns]# systemctl restart kubelet.service [ ~]# systemctl restart kubelet.service [ ~]# systemctl restart kubelet.service
如何测试DNS是否生效呢，可以使用下面的配置进行测试。
[master skydns]# ls
skydns-rc.yaml skydns-svc.yaml test_dns_pod.yaml
[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"
[ skydns]# kubectl create -f test_dns_pod.yaml
pod "busybox2" created
[ skydns]# kubectl get pods
NAME READY STATUS RESTARTS AGE
busybox2 1/1 Running 0 20s
mysql-lmx4s 1/1 Running 0 59m
myweb-hsdwn 1/1 Running 0 45m
[ skydns]# kubectl exec -it busybox2 sh
/ #可以检测一下，svc的vip是否可以解析出来。
/ # nslookup mysql Server: 10.254.230.254 Address: 10.254.230.254:53 Name: mysql.default.svc.cluster.local Address: 10.254.207.238
可以看出来和SVC的地址一样。
[ ~]# kubectl get svc NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes 10.254.0.1 <none> 443/TCP 13d mysql 10.254.207.238 <none> 3306/TCP 1h myweb 10.254.29.22 <nodes> 8080:30008/TCP 46m [ ~]#
注意，刚才创建的dns服务，只有新起的pod里面才可以使用，如果已经存在的pod里面还没有使用dns服务的。如果想要之前的pod使用dns服务，需要将他们删除掉，重新创建一下的。
备注：如果配置好了DNS之后，创建的RC里面就可以不使用环境变量的地址（即VIP的地址），可以使用service（svc）的名称既可以找到这个service。
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