环境准备，上一节中的flask-redis项目，将项目启动：

docker-compose up -d
Starting flask-redis_web_1   ... done
Starting flask-redis_redis_1 ... done

查看状态：

docker-compose psName                      Command               State           Ports
-------------------------------------------------------------------------------------
flask-redis_redis_1   docker-entrypoint.sh redis ...   Up      6379/tcp
flask-redis_web_1     python app.py                    Up      0.0.0.0:8080->5000/tcp

docker-compose scale

我们目前的docker-compose 中的service容器中各自只有一个，通过scale可以去扩展service。

docker-compose up --help--scale SERVICE=NUM        Scale SERVICE to NUM instances. Overrides the`scale` setting in the Compose file if present.

例如将web服务的数量变为三个：

docker-compose up --scale web=3 -d
WARNING: The "web" service specifies a port on the host. If multiple containers for this service are created on a single host, the port will clash.
Starting flask-redis_web_1 ...
Starting flask-redis_web_1 ... done
Creating flask-redis_web_2 ... error
Creating flask-redis_web_3 ... errorERROR: for flask-redis_web_2  Cannot start service web: driver failed programming external connectivity on endpoint flask-redis_web_2 (952f3eea8bdf14f0a94845fb6ef5039285f7ffe40620faca32f40643b802fa97): Bind for 0.0.0.0:8080 failed: port is already allocatedERROR: for flask-redis_web_3  Cannot start service web: driver failed programming external connectivity on endpoint flask-redis_web_3 (50c776deb73b272d04181a8ab385f27cc31689aeeed804436fd2b92836cf25b9): Bind for 0.0.0.0:8080 failed: port is already allocatedERROR: for web  Cannot start service web: driver failed programming external connectivity on endpoint flask-redis_web_2 (952f3eea8bdf14f0a94845fb6ef5039285f7ffe40620faca32f40643b802fa97): Bind for 0.0.0.0:8080 failed: port is already allocated
ERROR: Encountered errors while bringing up the project.

发现报错了，原因是接口已经被分配了。每个容器的端口都想绑定到8080上面，显然是不可能的。

将容器删除：

docker-compose down
Stopping flask-redis_web_1   ... done
Stopping flask-redis_redis_1 ... done
Removing flask-redis_web_3   ... done
Removing flask-redis_web_2   ... done
Removing flask-redis_web_1   ... done
Removing flask-redis_redis_1 ... done
Removing network flask-redis_default

将docker-compose.yml中端口绑定删除：

version: "3"services:redis:image: redisweb:build:context: .dockerfile: Dockerfileenvironment:REDIS_HOST: redis

执行命令docker-compose up --scale web=3 -d

docker-compose up --scale web=3 -d
Creating network "flask-redis_default" with the default driver
Creating flask-redis_web_1   ... done
Creating flask-redis_web_2   ... done
Creating flask-redis_web_3   ... done
Creating flask-redis_redis_1 ... done

可以成功执行。

docker-compose psName                      Command               State    Ports
-----------------------------------------------------------------------
flask-redis_redis_1   docker-entrypoint.sh redis ...   Up      6379/tcp
flask-redis_web_1     python app.py                    Up      5000/tcp
flask-redis_web_2     python app.py                    Up      5000/tcp
flask-redis_web_3     python app.py                    Up      5000/tcp

发现web端口并没有映射到主机的端口，全部是5000container端口。

想象一下假如有多个web服务，都会监听本地的5000端口，都会访问redis，那么我们就可以有一个负载均衡器，可以把访问量平均的分配到web服务，可以减轻单个服务的压力。如下图所示：

如果我们用这种方式来部署web服务的话，以后的扩展性是非常强的。例如我们开启10个web服务：

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis$ docker-compose up --scale web=10 -d
WARNING: The Docker Engine you're using is running in swarm mode.Compose does not use swarm mode to deploy services to multiple nodes in a swarm. All containers will be scheduled on the current node.To deploy your application across the swarm, use `docker stack deploy`.Creating network "docker-compose-flask-redis_default" with the default driver
Creating docker-compose-flask-redis_redis_1 ... done
Creating docker-compose-flask-redis_web_1   ... done
Creating docker-compose-flask-redis_web_2   ... done
Creating docker-compose-flask-redis_web_3   ... done
Creating docker-compose-flask-redis_web_4   ... done
Creating docker-compose-flask-redis_web_5   ... done
Creating docker-compose-flask-redis_web_6   ... done
Creating docker-compose-flask-redis_web_7   ... done
Creating docker-compose-flask-redis_web_8   ... done
Creating docker-compose-flask-redis_web_9   ... done
Creating docker-compose-flask-redis_web_10  ... done

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis$ docker-compose psName                             Command               State    Ports
--------------------------------------------------------------------------------------
docker-compose-flask-redis_redis_1   docker-entrypoint.sh redis ...   Up      6379/tcp
docker-compose-flask-redis_web_1     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_10    python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_2     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_3     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_4     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_5     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_6     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_7     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_8     python app.py                    Up      5000/tcp
docker-compose-flask-redis_web_9     python app.py                    Up      5000/tcp

我们为了演示真实的架构，使用HAproxy做负载均衡

将app.py的端口由5000改为80，app.py如下：

from flask import Flask
from redis import Redis
import os
import socketapp = Flask(__name__)
redis = Redis(host=os.environ.get('REDIS_HOST', '127.0.0.1'), port=6379)@app.route('/')
def hello():redis.incr('hits')return 'Hello Container World! I have been seen %s times and my hostname is %s.\n' % (redis.get('hits'),socket.gethostname())if __name__ == "__main__":app.run(host="0.0.0.0", port=80, debug=True)

Dockerfile的expose也改成80，内容如下：

FROM python:3.5
LABEL maintaner="vincent"
COPY . /app
WORKDIR /app
RUN pip install flask redis
EXPOSE 80
CMD [ "python", "app.py" ]

docker-compose.yml中添加haproxy，内容如下：

version: "3"services:redis:image: redisweb:build:context: .dockerfile: Dockerfileenvironment:REDIS_HOST: redislb:image: dockercloud/haproxylinks:- webports:- 8082:80volumes:- /var/run/docker.sock:/var/run/docker.sock

将上面的容器先docker-compose down，将容器删掉。

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ docker-compose up -d
WARNING: The Docker Engine you're using is running in swarm mode.Compose does not use swarm mode to deploy services to multiple nodes in a swarm. All containers will be scheduled on the current node.To deploy your application across the swarm, use `docker stack deploy`.Removing docker-compose-flask-redis-haproxy_lb_1
docker-compose-flask-redis-haproxy_redis_1 is up-to-date
docker-compose-flask-redis-haproxy_web_1 is up-to-date
Recreating d2b87be02ede_docker-compose-flask-redis-haproxy_lb_1 ... done

查看状态：

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ docker-compose psName                                 Command               State                    Ports
-----------------------------------------------------------------------------------------------------------------------------
docker-compose-flask-redis-haproxy_lb_1      /sbin/tini -- dockercloud- ...   Up      1936/tcp, 443/tcp, 0.0.0.0:8082->80/tcp
docker-compose-flask-redis-haproxy_redis_1   docker-entrypoint.sh redis ...   Up      6379/tcp
docker-compose-flask-redis-haproxy_web_1     python app.py                    Up      80/tcp 

测试访问：

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'1' times and my hostname is 9603ec0f2527.

测试通过。

接下来测试使用多个web服务：

先将之前的docker-compose down。

启动三个web服务：

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ docker-compose up --scale web=3 -d
WARNING: The Docker Engine you're using is running in swarm mode.Compose does not use swarm mode to deploy services to multiple nodes in a swarm. All containers will be scheduled on the current node.To deploy your application across the swarm, use `docker stack deploy`.Creating network "docker-compose-flask-redis-haproxy_default" with the default driver
Creating docker-compose-flask-redis-haproxy_web_1   ... done
Creating docker-compose-flask-redis-haproxy_web_2   ... done
Creating docker-compose-flask-redis-haproxy_web_3   ... done
Creating docker-compose-flask-redis-haproxy_redis_1 ... done
Creating docker-compose-flask-redis-haproxy_lb_1    ... done

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ docker-compose psName                                 Command               State                    Ports
-----------------------------------------------------------------------------------------------------------------------------
docker-compose-flask-redis-haproxy_lb_1      /sbin/tini -- dockercloud- ...   Up      1936/tcp, 443/tcp, 0.0.0.0:8082->80/tcp
docker-compose-flask-redis-haproxy_redis_1   docker-entrypoint.sh redis ...   Up      6379/tcp
docker-compose-flask-redis-haproxy_web_1     python app.py                    Up      80/tcp
docker-compose-flask-redis-haproxy_web_2     python app.py                    Up      80/tcp
docker-compose-flask-redis-haproxy_web_3     python app.py                    Up      80/tcp

依次访问我们的HAproxy：

iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'1' times and my hostname is 9a2d714aadad.
iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'2' times and my hostname is eda311882f3f.
iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'3' times and my hostname is 43f69f733c5e.
iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'4' times and my hostname is 9a2d714aadad.
iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'5' times and my hostname is eda311882f3f.
iie4bu@hostdocker:~/ddy/docker-compose-flask-redis-haproxy$ curl 127.0.0.1:8082
Hello Container World! I have been seen b'6' times and my hostname is 43f69f733c5e.

发现是轮询我们的web服务，haproxy会转发请求到三个web服务上。

我们目前的扩展是单机环境下的scale，无论将service扩展到多少，只能限制在单机环境下。但是一台服务器的资源是有限的，那么如何扩展多台服务器？那么就是需要使用swarm技术了。