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Service discovery and load balancing mechanism -service

2022-07-03 21:02:00 【Zhong Ming】

What is? Service？

Service Is a logical group Pod, One can access Pod The strategy of , And other Pod Can pass Service Visit this Service Acting Pod, It can be understood as the reverse proxy in the traditional architecture .
be relative to Pod for ,Service Have a fixed name , No change , It also provides the function of load balancing .
adopt Service The definition of , You can mask the backend for client applications Pod Number of instances and Pod IP Address change , The load balancing strategy is used to realize the request to the back end Pod Forwarding of instances , Provide a stable service access portal address for client applications .
Service It implements several core functions in the microservice architecture ： Automatic service registration 、 Service discovery 、 Service load balancing, etc .

Create a Service example

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-svc
  name: nginx-svc
spec:
  ports:
  - name: http #service Port name 
    port: 80 #service Own port 
    protocol: TCP # Support TCP UDP SCTP etc. 
    targetPort: 80 # Back end application interface 
  - name: https
    port: 443
    protocol: TCP
    targetPort: 443
  selector:
    app: nginx  # This is the matching rule , The proxy tag contains nginx The back-end server 
  sessionAffinity: None
  type: ClusterIP

Execute the above yaml file , Create a service

[[email protected]-master01 ~]# kubectl create -f nginx-svc.yaml 
service/nginx-svc created
[[email protected]-master01 ~]# kubectl get svc
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP          9d
nginx-svc    ClusterIP   10.110.150.87   <none>        80/TCP,443/TCP   15s

We have access to svc Address to access the back-end nginx

[[email protected]-master01 ~]# curl 10.110.150.87
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html {
     color-scheme: light dark; }
body {
     width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

In the same namespace in , other Pod visit svc It only needs curl http://nginx-svc Can
Span namespace Words , Need to be in svc Add after name .namespace name That's all right. , Use with caution , There is no need not to recommend
It is not recommended to pass IP Address access , because IP Not fixed , After deletion or reconstruction IP Will randomly generate

Be careful , The above content can only be accessed within the cluster

————————————————————————

If you want to access... Outside the cluster svc Words , Below

Use Service agent k8s External application scenarios

Want to use a fixed name in production instead of IP Address to access external middleware services
hope Service Point to the other namespace Services in or other clusters
A project is being migrated to k8s colony , But some services are still outside the cluster , You can use service Agent external services

Create a proxy for external applications Service example

Let's define an external application service

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-svc-w
  name: nginx-svc-w
spec:
  ports:
  - name: http 
    port: 80 
    protocol: TCP 
    targetPort: 80 
# - name: https
# port: 443
# protocol: TCP
# targetPort: 443
# selector:
# app: nginx 
  sessionAffinity: None
  type: ClusterIP

The difference is that these two parameters are missing ：

  selector:
    app: nginx

View after creation , It can be found that although the creation was successful, there was no ENDPOINTS

[[email protected]-master01 ~]# kubectl get svc
NAME          TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
kubernetes    ClusterIP   10.96.0.1       <none>        443/TCP          9d
nginx-svc     ClusterIP   10.110.150.87   <none>        80/TCP,443/TCP   31m
nginx-svc-w   ClusterIP   10.110.144.61   <none>        80/TCP           58s
[[email protected]-master01 ~]# kubectl get ep
NAME         ENDPOINTS                                                          AGE
kubernetes   192.168.10.2:6443,192.168.10.3:6443,192.168.10.4:6443              9d
nginx-svc    172.17.125.10:443,172.18.195.22:443,172.17.125.10:80 + 1 more...   31m

Next we need to manually create a custom ENDPOINTS
Borrow existing ep Make a new one ep file

[[email protected]-master01 ~]# kubectl get ep nginx-svc -o yaml > nginx-ep-w.yaml

apiVersion: v1
kind: Endpoints
metadata:
  labels:
    app: nginx-svc-w
  name: nginx-svc-w
  namespace: default
subsets:
- addresses:
  - ip: 110.242.68.3 #  The address of the external service of the proxy 
  ports:
  - name: http
    port: 80
    protocol: TCP

You can see that there are already external agents

[[email protected]-master01 ~]# kubectl create -f nginx-ep-w.yaml 
endpoints/nginx-svc-w created
[[email protected]-master01 ~]# kubectl get ep
NAME          ENDPOINTS                                                          AGE
kubernetes    192.168.10.2:6443,192.168.10.3:6443,192.168.10.4:6443              9d
nginx-svc     172.17.125.10:443,172.18.195.22:443,172.17.125.10:80 + 1 more...   47m
nginx-svc-w   110.242.68.3:80                                                    11s

Next, try whether you can access it successfully

#  Direct access makes sense , Return value 200
[[email protected]-master01 ~]# curl baidu.com -I
HTTP/1.1 200 OK
Date: Mon, 14 Feb 2022 01:43:18 GMT
Server: Apache
Last-Modified: Tue, 12 Jan 2010 13:48:00 GMT
ETag: "51-47cf7e6ee8400"
Accept-Ranges: bytes
Content-Length: 81
Cache-Control: max-age=86400
Expires: Tue, 15 Feb 2022 01:43:18 GMT
Connection: Keep-Alive
Content-Type: text/html
#  By visiting service Of IP It can be seen that it is also true , Return value 200
[[email protected]-master01 ~]# curl 10.110.144.61 -I
HTTP/1.1 200 OK
Date: Mon, 14 Feb 2022 01:44:20 GMT
Server: Apache
Last-Modified: Tue, 12 Jan 2010 13:48:00 GMT
ETag: "51-47cf7e6ee8400"
Accept-Ranges: bytes
Content-Length: 81
Cache-Control: max-age=86400
Expires: Tue, 15 Feb 2022 01:44:20 GMT
Connection: Keep-Alive
Content-Type: text/html

If the business changes ep What if the address changes ? Only need ep Change the address of the agent .
For example, we change one taobao Address test for ：

#  Take out taobao Of IP
[[email protected]-master01 ~]# ping taobao.com
PING taobao.com (140.205.94.189) 56(84) bytes of data.
64 bytes from 140.205.94.189 (140.205.94.189): icmp_seq=1 ttl=128 time=27.4 ms
64 bytes from 140.205.94.189 (140.205.94.189): icmp_seq=2 ttl=128 time=27.4 ms
#  modify ep Of yaml file ：nginx-ep-w.yaml
apiVersion: v1
kind: Endpoints
metadata:
  labels:
    app: nginx-svc-w
  name: nginx-svc-w
  namespace: default
subsets:
- addresses:
  - ip: 140.205.94.189 # taobao
  ports:
  - name: http
    port: 80
    protocol: TCP
#  Reload 
[[email protected]-master01 ~]# kubectl replace -f nginx-ep-w.yaml

Visit and test to see if it is connected ： This returns 501 No problem .

[[email protected]-master01 ~]# curl 10.110.144.61 -I
HTTP/1.1 501 Not Implemented
Server: Tengine
Date: Mon, 14 Feb 2022 01:39:16 GMT
Content-Type: text/html
Content-Length: 583
Connection: close

Service Reverse the external domain name

Let's not talk about this , Just know how to match it .
Service Of yaml file ：

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-svc-wname
  name: nginx-svc-wname
spec:
  type: ExternalName
  externalName: www.baidu.com

Then create it ：

kubectl apply -f nginx-svc-wname.yaml

Service The type of ：

ClusterIP： Use within the cluster , Default
ExternalName： By returning the defined CNAME Alias
NodePort： In all installed kube-proxy Open a port on the node of , This port can proxy to the back end Pod, Then the nodes can be used outside the cluster IP Address and NodePort The port number accesses the cluster Pod service . The default port value range is 30000-32767
LoadBalancer： Use the load balancer provided by the cloud service provider to expose the service

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版权声明
本文为[Zhong Ming]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/02/202202142337556328.html