服务自发现，是在服务启动后，有自发现服务自己发现启动服务的 IP 和 Port 并保存下来提供使用。
在 K8S 中，服务自发现通过两种方式：环境变量或 DNS。在没有 DNS 的时候， K8S 就用环境变量的方式，但一旦有很多 Service，环境变量就会变得极其复杂（每个服务都会有对应的环境变量），我们就需要用 DNS 的方式。
安装 DNS 服务
下载资料包： https://www.qstack.com.cn/skydns.zip
资料中有三个文件：
- skydns-rc.yaml，是启动 dns 服务的（是个 Deployment）
- skydns-svc.yaml，启动服务，其中配置了端口
- test_dns_pod.yaml，用于测试
apiVersion: extensions/v1beta1
kind: Deployment # 资源类型
metadata:
name: kube-dns
namespace: kube-system # 指定了 namespace
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: # 升级属性
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 # 第一个镜像
resources: # 资源使用的请求和限制
# 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: # 容器的探针服务，检查有没有运行起来，4xx/5xx 为不正常
httpGet:
path: /healthz-kubedns
port: 8080
scheme: HTTP
initialDelaySeconds: 60
timeoutSeconds: 5
successThreshold: 1
failureThreshold: 5
readinessProbe: # 检查服务能否可用
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: # 参数，指定了域名、端口、配置
- --domain=cluster.local.
- --dns-port=10053
- --config-map=kube-dns
- --kube-master-url=http://172.16.156.128:8080 # 这里要改成自己 api-server 的地址
# 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 # 第二个容器
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 # 指标，配合做监控使用
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 # 健康检查的镜像
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.
# 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 # 指定了 namespace
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 # v IP 地址
ports:
- name: dns
port: 53
protocol: UDP
- name: dns-tcp
port: 53
protocol: TCP
注意，这两个文件都指定了 namespace。以下是查看所有跑起来服务的截图。
image.png
要想使用此 DNS，我们需要改一下所有 kubelet 的配置文件。
# /etc/kubernetes/kubelet
KUBELET_ARGS="--cluster_dns=10.254.230.254 --cluster_domain=cluster.local"
# 更改完后重启 kubelet： systemctl restart kubelet
测试 DNS 生效
资料包中 test_dns_pod.yaml 文件是通过 busybox 来测试 DNS 的
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"
通过创建它，并进入容器
kubectl create -f test_dns_pod.yaml
kubectl exec -it busybox2 sh # 此容器通过 sh 进入，没有 bash
在容器中查询其他服务的名称，结果可以查询到服务地址：
image.png
注意，只有新启动的服务才能使用 DNS 服务，如上面的 busybox，其他服务需要重启才能查询。
上文中 tomcat 连 mysql 服务的 ip 地址可以改为服务名进行连接。
image.png
最后重启 tomcat 服务。（连接数据库的项目没做，所以部分内容忽略，先做笔记做参考）
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