docker学习笔记(七)docker-swarm

官网:https://docs.docker.com/swarm/overview/

Docker Swarm is native clustering for Docker. It turns a pool of Docker hosts into a single, virtual Docker host.

Swarm 是 Docker 官方提供的集群管理工具，其主要作用是把若干台 Docker 主机抽象为一个整体，并且通过一个入口统一管理这些 Docker 主机上的各种 Docker 资源。

一个 Swarm由一个或多个可以互相通信的Docker 节点组成.
节点会被分为两类，Manager节点和Worker节点。
Manager负责控制集群，监控集群状态、分发任务至worker节点等操作;Worker节点则接收来自Master节点的任务并在其上执行
相当于Manager是包工头，Worker是底层实际干活的工人。

搭建Swarm环境

这里使用的docker在线环境 https://labs.play-with-docker.com/

(1)准备3台centos7机器
192.168.0.31 (Manager)
192.168.0.32 (Worker01)
192.168.0.33 (Worker02)
(2)初始化Manager节点
docker swarm init --advertise-addr=192.168.0.31
(3)将worker节点加入到集群里

docker swarm join --token SWMTKN-1-5rxv93eb0hg3mzxze2lukaye7rkqm5uvlyk30n2lk9h2z36j2t-650nf075oarceftbefx6palr2 192.168.0.31:2377

查看集群状态

(4)node类型的转换

#可以将worker提升成Manager节点，从而保证swarm的高可用
docker node promote node2
docker node promote node1

#降级可以用demote
docker node demote node2

swarm基本操作

Service是自 Docker 1.12 后新引入的概念，仅适用于 docker swarm

Service配置的属性和docker的容器属性基本一致，比如容器名、端口映射、network和image. Servcie可以简单理解为一组相同的容器副本

(1)创建一个tomcat的service
  docker service create --name my-tomcat tomcat
(2)查看当前swarm的service
  docker service ls
(3)查看service的启动日志
  docker service logs my-tomcat
(4)查看service的详情
  docker service inspect my-tomcat
(5)查看my-tomcat运行在哪个node上
docker service ps my-tomcat

(6)水平扩展service
docker service scale my-tomcat=3
docker service ls
docker service ps my-tomcat

(7)如果停掉一个node的container,service会自动帮我们维护容器副本，创建一个新的容器

(8)删除service
docker service rm my-tomcat

swarm实战

单机docker中使用bridge网络进行连接通信，多机中使用的是overlay网络

1)在manager节点创建一个overlay网络，用于docker swarm中多机通信
docker network create -d overlay my-overlay-net
docker network ls

(2)创建mysql和wordpress的service(Manager node)

docker service create --name mysql --mount type=volume,source=v1,destination=/var/lib/mysql -e MYSQL_ROOT_PASSWORD=examplepass -e MYSQL_DATABASE=db_wordpress --network my-overlay-net mysql:5.6

docker service create --name wordpress -e WORDPRESS_DB_USER=root -e WORDPRESS_DB_PASSWORD=examplepass -e WORDPRESS_DB_HOST=mysql:3306 -e WORDPRESS_DB_NAME=db_wordpress -p 8080:80 --network my-overlay-net wordpress

运行成功

通过各个node的ip:8080都能访问成功(这里我通过play-with-docker open port访问8080端口)

这里的wordpress连接mysql是通过服务名mysql来连接的，说明其中一定有dns解析,会根据serviceName查找到对应的ip,进行连接，这样在部署(扩容)的时候就无需关心容器的ip怎么变化

For most situations, you should connect to the service name, which is load-balanced and handled by all containers (“tasks”) backing the service .

docker swarm服务发布模式

Docker Swarm 支持两种服务发布模式：Ingress模式（默认),Host模式。
通过 Ingress 模式发布的服务，可以保证从 Swarm 集群内任一节点（即使没有运行服务的节点）都能访问该服务；以 Host 模式发布的服务只能通过运行服务副本的节点来访问。下图展示了两种模式的区别。

想要进一步了解ingress和服务发现的底层可以阅读以下文章:
https://www.jianshu.com/p/c83a9173459f
https://www.cnblogs.com/zonehoo/p/11401930.html

(1)单机部署一个tomcat service,各个集群node都可以访问到

[node3] (local) [email protected] ~
$ docker service create --name tomcat  -p 8080:8080 --network my-overlay-net tomcat
fywyxuvpbpurt3ha0pkq4wwyu
overall progress: 1 out of 1 tasks 
1/1: running   [==================================================>] 
verify: Service converged 
[node3] (local) [email protected] ~
$ docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
fywyxuvpbpur        tomcat              replicated          1/1                 tomcat:latest       *:8080->8080/tcp
$ docker service ps tomcat
ID                  NAME                IMAGE               NODE                DESIRED STATE       CURRENT STATE            ERROR               PORTS
8pjqve65ebww        tomcat.1            tomcat:latest       node1               Running             Running 40 seconds ago         

#该tomcat容器实际部署再node1上,container为4fa7
[node1] (local) [email protected] ~
$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
4fa7f6681778        tomcat:latest       "catalina.sh run"   5 minutes ago       Up 5 minutes        8080/tcp            tomcat.1.8pjqve65ebwwi3adp53eb3xbg

其他node节点都能通过访问本地的8080端口访问到该tomcat

(2)部署多副本的whoami service,可以通过serviceName进行负载均衡

[node3] (local) [email protected] ~
$ docker service create --name whoami -p 8000:8000 --network my-overlay-net -d  jwilder/whoami
k1d6tus51sirz9xd4elgz2xvm
[node3] (local) [email protected] ~
$ docker service ps whoami
ID                  NAME                IMAGE                   NODE                DESIRED STATE       CURRENT STATE            ERROR               PORTS
8kaudc0xvpdm        whoami.1            jwilder/whoami:latest   node3               Running             Running 10 seconds ago                       
[node3] (local) [email protected] ~
$ docker ps 
CONTAINER ID        IMAGE                   COMMAND             CREATED             STATUS              PORTS               NAMES
cb723685302a        jwilder/whoami:latest   "/app/http"         48 seconds ago      Up 47 seconds       8000/tcp            whoami.1.8kaudc0xvpdmax2k12nf7h6m5

#不同节点上的tomcat,whomi服务,可以容器内通过serviceName ping通
[node3] (local) [email protected] ~
$ docker exec -it cb72368  ping tomcat 
PING tomcat (10.0.0.2): 56 data bytes
64 bytes from 10.0.0.2: seq=0 ttl=64 time=0.117 ms
64 bytes from 10.0.0.2: seq=1 ttl=64 time=0.093 ms
64 bytes from 10.0.0.2: seq=2 ttl=64 time=0.097 ms
$ docker exec -it 4fa7 ping whoami
PING whoami (10.0.0.5) 56(84) bytes of data.
64 bytes from 10.0.0.5 (10.0.0.5): icmp_seq=1 ttl=64 time=0.137 ms
64 bytes from 10.0.0.5 (10.0.0.5): icmp_seq=2 ttl=64 time=0.052 ms
64 bytes from 10.0.0.5 (10.0.0.5): icmp_seq=3 ttl=64 time=0.061 ms

#扩容成3个副本,通过whoami:8000访问,返回不同的hostid
[node3] (local) [email protected] ~
$ docker service scale whoami=3
whoami scaled to 3
overall progress: 3 out of 3 tasks 
1/3: running   [==================================================>] 
2/3: running   [==================================================>] 
3/3: running   [==================================================>] 
verify: Service converged 
[node3] (local) [email protected] ~
$ docker service ps whoami 
ID                  NAME                IMAGE                   NODE                DESIRED STATE       CURRENT STATE           ERROR               PORTS
8kaudc0xvpdm        whoami.1            jwilder/whoami:latest   node3               Running             Running 3 minutes ago                       
4jv21432xgqo        whoami.2            jwilder/whoami:latest   node2               Running             Running 8 seconds ago                       
svg62zqee2g1        whoami.3            jwilder/whoami:latest   node1               Running             Running 8 seconds ago 

[node1] (local) [email protected] ~
$ docker exec -it 4fa7 curl whoami:8000
I'm bca5e1a05a00
[node1] (local) [email protected] ~
$ docker exec -it 4fa7 curl whoami:8000
I'm 6f25815a733c
[node1] (local) [email protected] ~
$ docker exec -it 4fa7 curl whoami:8000
I'm cb723685302a
[node1] (local) [email protected] ~
$ docker exec -it 4fa7 curl whoami:8000
I'm bca5e1a05a00

service对其他服务提供了一个统一的VIP入口，接收其他服务访问时会做负载均衡。

最好再画一张图。

docker stack

在docker中有docker-compose帮助简化部署操作，docker swarm中也可以使用docker stack来进行部署管理servcie
具体的定义方式跟compose差不多，这里就不一一解释了
(1)新建service.yml文件

version: '3'

services:

  wordpress:
    image: wordpress
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_USER: exampleuser
      WORDPRESS_DB_PASSWORD: examplepass
      WORDPRESS_DB_NAME: exampledb
    networks:
      - ol-net
    volumes:
      - wordpress:/var/www/html
    deploy:
      mode: replicated
      replicas: 3
      restart_policy:
        condition: on-failure
        delay: 5s
        max_attempts: 3
      update_config:
        parallelism: 1
        delay: 10s

  db:
    image: mysql:5.7
    environment:
      MYSQL_DATABASE: exampledb
      MYSQL_USER: exampleuser
      MYSQL_PASSWORD: examplepass
      MYSQL_RANDOM_ROOT_PASSWORD: '1'
    volumes:
      - db:/var/lib/mysql
    networks:
      - ol-net
    deploy:
      mode: global
      placement:
        constraints:
          - node.role == manager

volumes:
  wordpress:
  db:

networks:
  ol-net:
    driver: overlay

(2)根据service.yml创建service
docker statck deploy -c service.yml my-service
(3)常见操作
查看stack具体信息
docker stack ls

查看具体的service
docker stack services my-service