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？
1 [root@k8s-master ~]# kubectl get all -o wide 2 NAME DESIRED CURRENT READY AGE CONTAINER(S) IMAGE(S) SELECTOR 3 rc/mysql 1 1 1 16h mysql 192.168.110.133:5000/mysql:5.7.30 app=mysql 4 rc/myweb 1 1 1 1h myweb 192.168.110.133:5000/tomcat:latest app=myweb 5 6 NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR 7 svc/kubernetes 10.254.0.1 <none> 443/TCP 13d <none> 8 svc/mysql 10.254.245.194 <none> 3306/TCP 16h app=mysql 9 svc/myweb 10.254.222.197 <nodes> 8080:30008/TCP 1h app=myweb 10 11 NAME READY STATUS RESTARTS AGE IP NODE 12 po/mysql-537xf 1/1 Running 1 16h 172.16.16.3 k8s-master 13 po/myweb-8b7n3 1/1 Running 0 1h 172.16.32.3 k8s-node3 14 [root@k8s-master ~]# kubectl exec -it myweb-8b7n3 /bin/bas 15 base64 basename bash bashbug bashbug-64 16 [root@k8s-master ~]# kubectl exec -it myweb-8b7n3 /bin/bas 17 base64 basename bash bashbug bashbug-64 18 [root@k8s-master ~]# kubectl exec -it myweb-8b7n3 /bin/bash 19 root@myweb-8b7n3:/usr/local/tomcat# env 20 KUBERNETES_SERVICE_PORT_HTTPS=443 21 MYSQL_PORT=tcp://10.254.245.194:3306 22 MYSQL_PORT_3306_TCP_ADDR=10.254.245.194 23 KUBERNETES_SERVICE_PORT=443 24 MYSQL_PORT_3306_TCP_PORT=3306 25 HOSTNAME=myweb-8b7n3 26 JAVA_HOME=/usr/local/openjdk-11 27 GPG_KEYS=05AB33110949707C93A279E3D3EFE6B686867BA6 07E48665A34DCAFAE522E5E6266191C37C037D42 47309207D818FFD8DCD3F83F1931D684307A10A5 541FBE7D8F78B25E055DDEE13C370389288584E7 61B832AC2F1C5A90F0F9B00A1C506407564C17A3 79F7026C690BAA50B92CD8B66A3AD3F4F22C4FED 9BA44C2621385CB966EBA586F72C284D731FABEE A27677289986DB50844682F8ACB77FC2E86E29AC A9C5DF4D22E99998D9875A5110C01C5A2F6059E7 DCFD35E0BF8CA7344752DE8B6FB21E8933C60243 F3A04C595DB5B6A5F1ECA43E3B7BBB100D811BBE F7DA48BB64BCB84ECBA7EE6935CD23C10D498E23 28 JAVA_BASE_URL=https://github.com/AdoptOpenJDK/openjdk11-upstream-binaries/releases/download/jdk-11.0.7%2B10/OpenJDK11U-jdk_ 29 MYSQL_PORT_3306_TCP=tcp://10.254.245.194:3306 30 PWD=/usr/local/tomcat 31 JAVA_URL_VERSION=11.0.7_10 32 TOMCAT_SHA512=75e16a00e02782961a7753dc9afaf6d209afa5f22d320319778fd0ee5e3b47009da522ac735599f1739bff6e809c2da9081dbbd4b8de54a82cf5b8cfbd8030ff 33 TOMCAT_MAJOR=9 34 HOME=/root 35 LANG=C.UTF-8 36 KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443 37 TOMCAT_NATIVE_LIBDIR=/usr/local/tomcat/native-jni-lib 38 TERM=xterm 39 MYSQL_SERVICE_PORT=3306 40 CATALINA_HOME=/usr/local/tomcat 41 MYSQL_SERVICE_HOST=10.254.245.194 42 MYSQL_PORT_3306_TCP_PROTO=tcp 43 SHLVL=1 44 KUBERNETES_PORT_443_TCP_PROTO=tcp 45 KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1 46 LD_LIBRARY_PATH=/usr/local/tomcat/native-jni-lib 47 KUBERNETES_SERVICE_HOST=10.254.0.1 48 KUBERNETES_PORT=tcp://10.254.0.1:443 49 KUBERNETES_PORT_443_TCP_PORT=443 50 PATH=/usr/local/tomcat/bin:/usr/local/openjdk-11/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin 51 TOMCAT_VERSION=9.0.36 52 JAVA_VERSION=11.0.7 53 _=/usr/bin/env 54 root@myweb-8b7n3:/usr/local/tomcat# java -version 55 openjdk version "11.0.7" 2020-04-14 56 OpenJDK Runtime Environment 18.9 (build 11.0.7+10) 57 OpenJDK 64-Bit Server VM 18.9 (build 11.0.7+10, mixed mode) 58 root@myweb-8b7n3:/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。
1 root@myweb-hsdwn:/usr/local/tomcat# env | grep -iE 'kubernetes|mysql|myweb' 2 KUBERNETES_SERVICE_PORT_HTTPS=443 3 MYSQL_PORT=tcp://10.254.207.238:3306 4 MYSQL_PORT_3306_TCP_ADDR=10.254.207.238 5 KUBERNETES_SERVICE_PORT=443 6 MYSQL_PORT_3306_TCP_PORT=3306 7 HOSTNAME=myweb-hsdwn 8 MYSQL_PORT_3306_TCP=tcp://10.254.207.238:3306 9 KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443 10 MYSQL_SERVICE_PORT=3306 11 MYSQL_SERVICE_HOST=10.254.207.238 12 MYSQL_PORT_3306_TCP_PROTO=tcp 13 KUBERNETES_PORT_443_TCP_PROTO=tcp 14 KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1 15 KUBERNETES_SERVICE_HOST=10.254.0.1 16 KUBERNETES_PORT=tcp://10.254.0.1:443 17 KUBERNETES_PORT_443_TCP_PORT=443 18 root@myweb-hsdwn:/usr/local/tomcat#
1 root@myweb-hsdwn:/usr/local/tomcat# env | grep -iE 'kubernetes|mysql|myweb' | wc -l 2 16 3 root@myweb-hsdwn:/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：
1 [root@k8s-master tomcat_demo]# wget https://www.qstack.com.cn/skydns.zip 2 --2020-06-18 15:31:25-- https://www.qstack.com.cn/skydns.zip 3 Resolving www.qstack.com.cn (www.qstack.com.cn)... 123.125.46.149, 111.202.85.37 4 Connecting to www.qstack.com.cn (www.qstack.com.cn)|123.125.46.149|:443... connected. 5 HTTP request sent, awaiting response... 200 OK 6 Length: 3411 (3.3K) [application/zip] 7 Saving to: ‘skydns.zip’ 8 9 100%[======================================================================================>] 3,411 --.-K/s in 0s 10 11 2020-06-18 15:31:26 (40.5 MB/s) - ‘skydns.zip’ saved [3411/3411] 12 13 [root@k8s-master tomcat_demo]# ls 14 mysql-rc.yml mysql-svc.yml skydns.zip tomcat-rc.yml tomcat-svc.yml 15 [root@k8s-master tomcat_demo]# cd .. 16 [root@k8s-master k8s]# mv tomcat_demo/skydns.zip . 17 [root@k8s-master k8s]# ls 18 book-master.war deploy pod rc skydns.zip svc tomcat_demo tomcat_demo.zip 19 [root@k8s-master k8s]# unzip skydns.zip 20 Archive: skydns.zip 21 creating: skydns/ 22 inflating: skydns/skydns-rc.yaml 23 inflating: skydns/skydns-svc.yaml 24 inflating: skydns/test_dns_pod.yaml 25 [root@k8s-master k8s]# ls 26 book-master.war deploy pod rc skydns skydns.zip svc tomcat_demo tomcat_demo.zip 27 [root@k8s-master k8s]#
修改skydns-rc.yaml配置文件。
1 # Copyright 2016 The Kubernetes Authors. 2 # 3 # Licensed under the Apache License, Version 2.0 (the "License"); 4 # you may not use this file except in compliance with the License. 5 # You may obtain a copy of the License at 6 # 7 # http://www.apache.org/licenses/LICENSE-2.0 8 # 9 # Unless required by applicable law or agreed to in writing, software 10 # distributed under the License is distributed on an "AS IS" BASIS, 11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 # See the License for the specific language governing permissions and 13 # limitations under the License. 14 15 # TODO - At some point, we need to rename all skydns-*.yaml.* files to kubedns-*.yaml.* 16 # Should keep target in cluster/addons/dns-horizontal-autoscaler/dns-horizontal-autoscaler.yaml 17 # in sync with this file. 18 19 # __MACHINE_GENERATED_WARNING__ 20 21 apiVersion: extensions/v1beta1 22 kind: Deployment 23 metadata: 24 name: kube-dns 25 namespace: kube-system 26 labels: 27 k8s-app: kube-dns 28 kubernetes.io/cluster-service: "true" 29 spec: 30 replicas: 1 31 # replicas: not specified here: 32 # 1. In order to make Addon Manager do not reconcile this replicas parameter. 33 # 2. Default is 1. 34 # 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on. 35 strategy: 36 rollingUpdate: 37 maxSurge: 10% 38 maxUnavailable: 0 39 selector: 40 matchLabels: 41 k8s-app: kube-dns 42 template: 43 metadata: 44 labels: 45 k8s-app: kube-dns 46 annotations: 47 scheduler.alpha.kubernetes.io/critical-pod: '' 48 scheduler.alpha.kubernetes.io/tolerations: '[{"key":"CriticalAddonsOnly", "operator":"Exists"}]' 49 spec: 50 containers: 51 - name: kubedns 52 image: myhub.fdccloud.com/library/kubedns-amd64:1.9 53 resources: 54 # TODO: Set memory limits when we've profiled the container for large 55 # clusters, then set request = limit to keep this container in 56 # guaranteed class. Currently, this container falls into the 57 # "burstable" category so the kubelet doesn't backoff from restarting it. 58 limits: 59 memory: 170Mi 60 requests: 61 cpu: 100m 62 memory: 70Mi 63 livenessProbe: 64 httpGet: 65 path: /healthz-kubedns 66 port: 8080 67 scheme: HTTP 68 initialDelaySeconds: 60 69 timeoutSeconds: 5 70 successThreshold: 1 71 failureThreshold: 5 72 readinessProbe: 73 httpGet: 74 path: /readiness 75 port: 8081 76 scheme: HTTP 77 # we poll on pod startup for the Kubernetes master service and 78 # only setup the /readiness HTTP server once that's available. 79 initialDelaySeconds: 3 80 timeoutSeconds: 5 81 args: 82 - --domain=cluster.local. 83 - --dns-port=10053 84 - --config-map=kube-dns 85 - --kube-master-url=http://10.0.0.11:8080 86 # This should be set to v=2 only after the new image (cut from 1.5) has 87 # been released, otherwise we will flood the logs. 88 - --v=0 89 #__PILLAR__FEDERATIONS__DOMAIN__MAP__ 90 env: 91 - name: PROMETHEUS_PORT 92 value: "10055" 93 ports: 94 - containerPort: 10053 95 name: dns-local 96 protocol: UDP 97 - containerPort: 10053 98 name: dns-tcp-local 99 protocol: TCP 100 - containerPort: 10055 101 name: metrics 102 protocol: TCP 103 - name: dnsmasq 104 image: myhub.fdccloud.com/library/kube-dnsmasq-amd64:1.4 105 livenessProbe: 106 httpGet: 107 path: /healthz-dnsmasq 108 port: 8080 109 scheme: HTTP 110 initialDelaySeconds: 60 111 timeoutSeconds: 5 112 successThreshold: 1 113 failureThreshold: 5 114 args: 115 - --cache-size=1000 116 - --no-resolv 117 - --server=127.0.0.1#10053 118 #- --log-facility=- 119 ports: 120 - containerPort: 53 121 name: dns 122 protocol: UDP 123 - containerPort: 53 124 name: dns-tcp 125 protocol: TCP 126 # see: https://github.com/kubernetes/kubernetes/issues/29055 for details 127 resources: 128 requests: 129 cpu: 150m 130 memory: 10Mi 131 - name: dnsmasq-metrics 132 image: myhub.fdccloud.com/library/dnsmasq-metrics-amd64:1.0 133 livenessProbe: 134 httpGet: 135 path: /metrics 136 port: 10054 137 scheme: HTTP 138 initialDelaySeconds: 60 139 timeoutSeconds: 5 140 successThreshold: 1 141 failureThreshold: 5 142 args: 143 - --v=2 144 - --logtostderr 145 ports: 146 - containerPort: 10054 147 name: metrics 148 protocol: TCP 149 resources: 150 requests: 151 memory: 10Mi 152 - name: healthz 153 image: myhub.fdccloud.com/library/exechealthz-amd64:1.2 154 resources: 155 limits: 156 memory: 50Mi 157 requests: 158 cpu: 10m 159 # Note that this container shouldn't really need 50Mi of memory. The 160 # limits are set higher than expected pending investigation on #29688. 161 # The extra memory was stolen from the kubedns container to keep the 162 # net memory requested by the pod constant. 163 memory: 50Mi 164 args: 165 - --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null 166 - --url=/healthz-dnsmasq 167 - --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1:10053 >/dev/null 168 - --url=/healthz-kubedns 169 - --port=8080 170 - --quiet 171 ports: 172 - containerPort: 8080 173 protocol: TCP 174 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 [root@k8s-master skydns]# kubectl create -f skydns-rc.yaml 2 deployment "kube-dns" created 3 [root@k8s-master 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。
1 [root@k8s-master ~]# kubectl get svc 2 NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE 3 kubernetes 10.254.0.1 <none> 443/TCP 13d 4 mysql 10.254.207.238 <none> 3306/TCP 42m 5 myweb 10.254.29.22 <nodes> 8080:30008/TCP 28m 6 [root@k8s-master ~]#
创建svc的命令，如下所示：
1 [root@k8s-master skydns]# vim skydns-svc.yaml 2 [root@k8s-master skydns]# kubectl create -f skydns-svc.yaml 3 service "kube-dns" created 4 [root@k8s-master 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。
1 [root@k8s-master skydns]# kubectl get pod --namespace=kube-system 2 NAME READY STATUS RESTARTS AGE 3 kube-dns-778415672-f9ssw 4/4 Running 0 6m 4 [root@k8s-master skydns]#
1 [root@k8s-master skydns]# kubectl get all --namespace=kube-system 2 NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE 3 deploy/kube-dns 1 1 1 1 7m 4 5 NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE 6 svc/kube-dns 10.254.230.254 <none> 53/UDP,53/TCP 3m 7 8 NAME DESIRED CURRENT READY AGE 9 rs/kube-dns-778415672 1 1 1 7m 10 11 NAME READY STATUS RESTARTS AGE 12 po/kube-dns-778415672-f9ssw 4/4 Running 0 7m 13 [root@k8s-master 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。
1 [root@k8s-master skydns]# vim /etc/kubernetes/kubelet 2 [root@k8s-master skydns]# kubectl get svc --namespace=kube-system 3 NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE 4 kube-dns 10.254.230.254 <none> 53/UDP,53/TCP 9m 5 [root@k8s-master skydns]#
然后重启三台Node节点的kubelet服务。
1 [root@k8s-master skydns]# systemctl restart kubelet.service 2 3 [root@k8s-node2 ~]# systemctl restart kubelet.service 4 5 [root@k8s-node3 ~]# 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。
1 [root@k8s-master skydns]# ls 2 skydns-rc.yaml skydns-svc.yaml test_dns_pod.yaml 3 [root@k8s-master skydns]# cat test_dns_pod.yaml 4 apiVersion: v1 5 kind: Pod 6 metadata: 7 labels: 8 name: busybox 9 role: master 10 name: busybox2 11 spec: 12 containers: 13 - name: busybox 14 image: docker.io/busybox:latest 15 imagePullPolicy: IfNotPresent 16 command: 17 - sleep 18 - "3600" 19 [root@k8s-master skydns]# kubectl create -f test_dns_pod.yaml 20 pod "busybox2" created 21 [root@k8s-master skydns]# kubectl get pods 22 NAME READY STATUS RESTARTS AGE 23 busybox2 1/1 Running 0 20s 24 mysql-lmx4s 1/1 Running 0 59m 25 myweb-hsdwn 1/1 Running 0 45m 26 [root@k8s-master skydns]# kubectl exec -it busybox2 sh 27 / #
可以检测一下，svc的vip是否可以解析出来。
1 / # nslookup mysql 2 Server: 10.254.230.254 3 Address: 10.254.230.254:53 4 5 Name: mysql.default.svc.cluster.local 6 Address: 10.254.207.238
可以看出来和SVC的地址一样。
1 [root@k8s-master ~]# kubectl get svc 2 NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE 3 kubernetes 10.254.0.1 <none> 443/TCP 13d 4 mysql 10.254.207.238 <none> 3306/TCP 1h 5 myweb 10.254.29.22 <nodes> 8080:30008/TCP 46m 6 [root@k8s-master ~]#
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。