Docker學習筆記（四）Service

       最簡單的情況下，我們的應用運行在一個container中，能夠提供的服務和性能非常有限。在實際項目中，應用大多是一般由大量的service組成，比如鑑權、告警等等。當然，每個service也可以有多個instance，來達到高性能和高可用性的目的。

       在docker中部署應用時，每個service有自己的image，並且一個service可以啓動多個container，service中的單個container叫作task。docker通過yml配置來定義service的生命週期，簡化service的部署，下面使用筆記三中build的image來演示service的基本應用。

Note

本文demo參考docker官方文檔，有條件的朋友建議直接看原文Link：https://docs.docker.com/get-started/part3/#recap-and-cheat-sheet-optional

hello-service demo

創建service-hello.yml文件

version: "3"
services:
  web:
    # replace username/repo:tag with your name and image details
    image: hebostary/gohead:demo1
    deploy:
      replicas: 5
      resources:
        limits:
          cpus: "0.1"
          memory: 50M
      restart_policy:
        condition: on-failure
    ports:
      - "4000:80"
    networks:
      - webnet
networks:
  webnet:

部署service

docker swarm init #first deploy need
docker stack deploy -c docker-service.yml hello-service

查詢servservice及container

[root@izuf682lz6444cynn96up0z service]# docker service ls
ID            NAME               MODE        REPLICAS  IMAGE
dpwa2lyvnrly  hello-service_web  replicated  5/5       hebostary/gohead:demo1
[root@izuf682lz6444cynn96up0z service]# docker service ps hello-service_web
ID            NAME                 IMAGE                   NODE                     DESIRED STATE  CURRENT STATE           ERROR  PORTS
ywf3ge6efoh0  hello-service_web.1  hebostary/gohead:demo1  izuf682lz6444cynn96up0z  Running        Running 40 seconds ago         
v4djymxdqopb  hello-service_web.2  hebostary/gohead:demo1  izuf682lz6444cynn96up0z  Running        Running 40 seconds ago         
j6qfm5k170n1  hello-service_web.3  hebostary/gohead:demo1  izuf682lz6444cynn96up0z  Running        Running 40 seconds ago         
g4t1etgfja8v  hello-service_web.4  hebostary/gohead:demo1  izuf682lz6444cynn96up0z  Running        Running 40 seconds ago         
sou1glk6ygtw  hello-service_web.5  hebostary/gohead:demo1  izuf682lz6444cynn96up0z  Running        Running 40 seconds ago         
[root@izuf682lz6444cynn96up0z service]# docker container ls
CONTAINER ID        IMAGE                                                                                      COMMAND             CREATED              STATUS              PORTS               NAMES
0043de2a9c83        hebostary/gohead@sha256:969c4f12d7c1d9e3f167498e1779aceefc631a158ec4e18730d16f5602569d03   "python app.py"     About a minute ago   Up About a minute   80/tcp              hello-service_web.2.v4djymxdqopb4ib9ilto9xvhm
e483dd3fcce9        hebostary/gohead@sha256:969c4f12d7c1d9e3f167498e1779aceefc631a158ec4e18730d16f5602569d03   "python app.py"     About a minute ago   Up About a minute   80/tcp              hello-service_web.3.j6qfm5k170n12k60huesg1lpl
377dc8046ba9        hebostary/gohead@sha256:969c4f12d7c1d9e3f167498e1779aceefc631a158ec4e18730d16f5602569d03   "python app.py"     About a minute ago   Up About a minute   80/tcp              hello-service_web.1.ywf3ge6efoh0mvxxg09gfgjle
32834e797374        hebostary/gohead@sha256:969c4f12d7c1d9e3f167498e1779aceefc631a158ec4e18730d16f5602569d03   "python app.py"     About a minute ago   Up About a minute   80/tcp              hello-service_web.5.sou1glk6ygtwdjphmdwnf2c5w
682f529a98ab        hebostary/gohead@sha256:969c4f12d7c1d9e3f167498e1779aceefc631a158ec4e18730d16f5602569d03   "python app.py"     About a minute ago   Up About a minute   80/tcp              hello-service_web.4.g4t1etgfja8vf8bzgxcfv3s2f

note：前面部署的service的名字是hello-service_web。hello-service實際上是stack，這個概念在後面會做描述。

[root@izuf682lz6444cynn96up0z service]# docker stack ls
NAME           SERVICES
hello-service  1

訪問http://ip:4000

Hello World!

Hostname: 32834e797374
Visits: cannot connect to Redis, counter disabled

每次訪問返回的Hostname幾乎都是不一樣的，這個hostname就是container的ID。這也說明，hello-service_web的5個instance共同分擔了多次請求的處理，有loadbalance的過程。

增加instance（scale）

將yml中的replicas修改成6，然後再次deploy，看到docker只是add了一個新的container，並沒有去修改原有的5個container。[root@izuf682lz6444cynn96up0z service]# docker stack deploy -c docker-service.yml hello-service Updating service hello-service_web (id: dpwa2lyvnrly17fz9ey3itba0)

刪除service

[root@izuf682lz6444cynn96up0z service]# docker stack rm hello-service
Removing service hello-service_web
Removing network hello-service_webnet
[root@izuf682lz6444cynn96up0z service]# docker swarm leave --force
Node left the swarm.

用到的命令

docker stack ls                                            # List stacks or apps
docker stack deploy -c <composefile> <appname>  # Run the specified Compose file
docker service ls                 # List running services associated with an app
docker service ps <service>                  # List tasks associated with an app
docker inspect <task or container>                   # Inspect task or container
docker container ls -q                                      # List container IDs
docker stack rm <appname>                             # Tear down an application
docker swarm leave --force      # Take down a single node swarm from the manager