擼了今年阿里、頭條和美團的面試，我有一個重要發現.......>>>

環境準備，上一節中的flask-redis項目，將項目啟動：

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

查看狀態：

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?

我們目前的docker-compose 中的service容器中各自只有一個，通過scale可以去擴展service。

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

例如將web服務的數量變為三個：

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.

發現報錯了，原因是接口已經被分配了。每個容器的端口都想綁定到8080上面，顯然是不可能的。

將容器刪除：

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

將docker-compose.yml中端口綁定刪除：

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

執行命令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

可以成功執行。

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

發現web端口并沒有映射到主機的端口，全部是5000container端口。

想象一下假如有多個web服務，都會監聽本地的5000端口，都會訪問redis，那么我們就可以有一個負載均衡器，可以把訪問量平均的分配到web服務，可以減輕單個服務的壓力。如下圖所示：

如果我們用這種方式來部署web服務的話，以后的擴展性是非常強的。例如我們開啟10個web服務：

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

我們為了演示真實的架構，使用HAproxy做負載均衡

將app.py的端口由5000改為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，內容如下：

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，內容如下：

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

將上面的容器先docker-compose down，將容器刪掉。

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

查看狀態：

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

測試訪問：

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.

測試通過。

接下來測試使用多個web服務：

先將之前的docker-compose down。

啟動三個web服務：

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

依次訪問我們的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.

發現是輪詢我們的web服務，haproxy會轉發請求到三個web服務上。

我們目前的擴展是單機環境下的scale，無論將service擴展到多少，只能限制在單機環境下。但是一臺服務器的資源是有限的，那么如何擴展多臺服務器？那么就是需要使用swarm技術了。

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