- 由 zhongluqiang创建, 最后修改于5月 07, 2022
docker compose 介绍
用于单机环境的容器编排,把一次性要创建的镜像、容器、网络、数据卷等内容写到docker-compose.yml
里去,然后通过docker-compose up
一条指令把全部的容器都跑起来。
除了可以批量启动容器,docker compose还可以实现水平扩展、管理环境变量、指定容器启动顺序、健康检查等功能。
docker compose 的安装
Windows和Mac在默认安装了docker desktop以后,docker-compose随之自动安装。
PS C:\Users\Peng Xiao\docker.tips> docker-compose --version docker-compose version 1.29.2, build 5becea4c
Linux用户需要自行安装,最新版本号可以在这里查询 https://github.com/docker/compose/releases。
$ sudo curl -L "https://github.com/docker/compose/releases/download/1.29.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose $ sudo chmod +x /usr/local/bin/docker-compose $ docker-compose --version docker-compose version 1.29.2, build 5becea4c
熟悉python的朋友,可以使用pip去安装docker-compose:
$ pip install docker-compose
compose文件语法结构
docker compose文件的语法说明 https://docs.docker.com/compose/compose-file/。
以下是一个典型的compose文件示例:
version: "3.8" services: # 容器 servicename: # 服务名字,这个名字也是内部 bridge网络可以使用的 DNS name image: # 镜像的名字 command: # 可选,如果设置,则会覆盖默认镜像里的 CMD命令 environment: # 可选,相当于 docker run里的 --env volumes: # 可选,相当于docker run里的 -v networks: # 可选,相当于 docker run里的 --network ports: # 可选,相当于 docker run里的 -p servicename2: volumes: # 可选,相当于 docker volume create networks: # 可选,相当于 docker network create
以Python Flask + Redis 练习为例子,改造成一个docker-compose文件:
docker image pull redis docker image build -t flask-demo . # create network docker network create -d bridge demo-network # create container docker container run -d --name redis-server --network demo-network redis docker container run -d --network demo-network --name flask-demo --env REDIS_HOST=redis-server -p 5000:5000 flask-demo
version: "3.8" services: flask-demo: image: flask-demo:latest environment: - REDIS_HOST=redis-server networks: - demo-network ports: - 8080:5000 redis-server: image: redis:latest networks: - demo-network networks: demo-network:
docker compose 水平扩展
源码结构
├── docker-compose.yml └── flask ├── Dockerfile └── app.py
from flask import Flask from redis import Redis import os import socket app = Flask(__name__) redis = Redis(host=os.environ.get('REDIS_HOST', '127.0.0.1'), port=6379) @app.route('/') def hello(): redis.incr('hits') return f"Hello Container World! I have been seen {redis.get('hits').decode('utf-8')} times and my hostname is {socket.gethostname()}.\n"
FROM python:3.9.5-slim RUN pip install flask redis && \ groupadd -r flask && useradd -r -g flask flask && \ mkdir /src && \ chown -R flask:flask /src USER flask COPY app.py /src/app.py WORKDIR /src ENV FLASK=app.py REDIS_HOST=redis EXPOSE 5000 CMD ["flask", "run", "-h", "0.0.0.0"]
version: "3.8" services: flask: build: context: ./flask dockerfile: Dockerfile image: flask-demo:latest environment: - REDIS_HOST=redis-server redis-server: image: redis:latest client: image: xiaopeng163/net-box:latest command: sh -c "while true; do sleep 3600; done;"
环境清理
删除容器和之前构建的镜像:
$ docker container rm -f $(docker container ps -aq) $ docker image rm flask
启动
$ docker-compose pull $ docker-compose build $ docker-compose up -d Creating network "compose-scale-example_default" with the default driver Creating compose-scale-example_flask_1 ... done Creating compose-scale-example_client_1 ... done Creating compose-scale-example_redis-server_1 ... done $ docker-compose ps Name Command State Ports ---------------------------------------------------------------------------------------- compose-scale-example_client_1 sh -c while true; do sleep ... Up compose-scale-example_flask_1 flask run -h 0.0.0.0 Up 5000/tcp compose-scale-example_redis-server_1 docker-entrypoint.sh redis ... Up 6379/tcp
水平扩展 scale
$ docker-compose up -d --scale flask=3 compose-scale-example_client_1 is up-to-date compose-scale-example_redis-server_1 is up-to-date Creating compose-scale-example_flask_2 ... done Creating compose-scale-example_flask_3 ... done $ docker-compose ps Name Command State Ports ---------------------------------------------------------------------------------------- compose-scale-example_client_1 sh -c while true; do sleep ... Up compose-scale-example_flask_1 flask run -h 0.0.0.0 Up 5000/tcp compose-scale-example_flask_2 flask run -h 0.0.0.0 Up 5000/tcp compose-scale-example_flask_3 flask run -h 0.0.0.0 Up 5000/tcp compose-scale-example_redis-server_1 docker-entrypoint.sh redis ... Up 6379/tcp
添加nginx实现负载均衡
源码结构如下,增加nginx作为反向代理:
├── docker-compose.yml ├── flask │ ├── Dockerfile │ └── app.py └── nginx └── nginx.conf
server { listen 80 default_server; location / { proxy_pass http://flask:5000; } }
version: "3.8" services: flask: build: context: ./flask dockerfile: Dockerfile image: flask-demo:latest environment: - REDIS_HOST=redis-server networks: - backend - frontend redis-server: image: redis:latest networks: - backend nginx: image: nginx:stable-alpine ports: - 8000:80 depends_on: - flask volumes: - ./nginx/nginx.conf:/etc/nginx/conf.d/default.conf:ro - ./var/log/nginx:/var/log/nginx networks: - frontend networks: backend: frontend:
验证步骤:
- 运行docker-compose up -d
- 浏览器访问localhost:8000
- 刷新网页
- 运行docker-compose up -d --scale flask=3,把flask容器水平扩展成3个
- 再次刷新网页,可以看到请求被平摊到3个flask容器上。
docker compose 环境变量
参考文档:https://docs.docker.com/compose/environment-variables/。
通过.env文件指定docker-compose要用到的环境变量,通过environment字段设置容器运行的环境变量。
.env文件一般会添加到.gitignore和.dockerignore中。
下面的示例通过环境变量来设置redis镜像启动时的密码,flask通过读取系统环境变量获得redis主机的密码。
├── .env ├── docker-compose.yml ├── flask │ ├── Dockerfile │ └── app.py └── nginx └── nginx.conf
from flask import Flask from redis import StrictRedis import os import socket app = Flask(__name__) redis = StrictRedis(host=os.environ.get('REDIS_HOST', '127.0.0.1'), port=6379, password=os.environ.get('REDIS_PASS')) @app.route('/') def hello(): redis.incr('hits') return f"Hello Container World! I have been seen {redis.get('hits').decode('utf-8')} times and my hostname is {socket.gethostname()}.\n"
REDIS_PASSWORD=ABC123
version: "3.8" services: flask: build: context: ./flask dockerfile: Dockerfile image: flask-demo:latest environment: - REDIS_HOST=redis-server - REDIS_PASS=${REDIS_PASSWORD} networks: - backend - frontend redis-server: image: redis:latest command: redis-server --requirepass ${REDIS_PASSWORD} networks: - backend nginx: image: nginx:stable-alpine ports: - 8000:80 depends_on: - flask volumes: - ./nginx/nginx.conf:/etc/nginx/conf.d/default.conf:ro - ./var/log/nginx:/var/log/nginx networks: - frontend networks: backend: frontend:
docker compose 服务依赖和健康检查
关于健康检查:
- https://docs.docker.com/engine/reference/builder/#healthcheck
- https://docs.docker.com/compose/compose-file/compose-file-v3/#healthcheck
健康检查是容器运行状态的高级检查,主要是检查容器所运行的进程是否能正常的对外提供“服务”,比如一个数据库容器,我们不光 需要这个容器是up的状态,我们还要求这个容器的数据库进程能够正常对外提供服务,这就是所谓的健康检查。
容器的健康检查
容器本身有一个健康检查的功能,但是需要在Dockerfile里定义,或者在执行docker container run 的时候,通过下面的一些参数指定:
--health-cmd string Command to run to check health --health-interval duration Time between running the check (ms|s|m|h) (default 0s) --health-retries int Consecutive failures needed to report unhealthy --health-start-period duration Start period for the container to initialize before starting health-retries countdown (ms|s|m|h) (default 0s) --health-timeout duration Maximum time to allow one check to
示例源码
我们以下面的这个flask容器为例,相关的代码如下:
from flask import Flask from redis import StrictRedis import os import socket app = Flask(__name__) redis = StrictRedis(host=os.environ.get('REDIS_HOST', '127.0.0.1'), port=6379, password=os.environ.get('REDIS_PASS')) @app.route('/') def hello(): redis.incr('hits') return f"Hello Container World! I have been seen {redis.get('hits').decode('utf-8')} times and my hostname is {socket.gethostname()}.\n"
FROM python:3.9.5-slim RUN pip install flask redis && \ apt-get update && \ apt-get install -y curl && \ groupadd -r flask && useradd -r -g flask flask && \ mkdir /src && \ chown -R flask:flask /src USER flask COPY app.py /src/app.py WORKDIR /src ENV FLASK_APP=app.py REDIS_HOST=redis EXPOSE 5000 HEALTHCHECK --interval=30s --timeout=3s \ CMD curl -f http://localhost:5000/ || exit 1 CMD ["flask", "run", "-h", "0.0.0.0"]
上面Dockerfili里的HEALTHCHECK 就是定义了一个健康检查。 会每隔30秒检查一次,如果失败就会退出,退出代码是1。
构建镜像和创建容器
构建镜像,创建一个bridge网络,然后启动容器连到bridge网络:
$ docker image build -t flask-demo . $ docker network create mybridge $ docker container run -d --network mybridge --env REDIS_PASS=abc123 flask-demo
查看容器状态:
$ docker container ls CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 059c12486019 flask-demo "flask run -h 0.0.0.0" 4 hours ago Up 8 seconds (health: starting) 5000/tcp dazzling_tereshkova
也可以通过docker container inspect 059 查看详情, 其中有有关health的:
"Health": { "Status": "starting", "FailingStreak": 1, "Log": [ { "Start": "2021-07-14T19:04:46.4054004Z", "End": "2021-07-14T19:04:49.4055393Z", "ExitCode": -1, "Output": "Health check exceeded timeout (3s)" } ] }
经过3次检查,一直是不通的,然后health的状态会从starting变为 unhealthy:
docker container ls CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 059c12486019 flask-demo "flask run -h 0.0.0.0" 4 hours ago Up 2 minutes (unhealthy) 5000/tcp dazzling_tereshkova
启动redis服务器
启动redis,连到mybridge上,name=redis, 注意密码:
$ docker container run -d --network mybridge --name redis redis:latest redis-server --requirepass abc123
经过几秒钟,我们的flask 变成了healthy:
$ docker container ls CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES bc4e826ee938 redis:latest "docker-entrypoint.s…" 18 seconds ago Up 16 seconds 6379/tcp redis 059c12486019 flask-demo "flask run -h 0.0.0.0" 4 hours ago Up 6 minutes (healthy) 5000/tcp dazzling_tereshkova
一个healthcheck不错的例子 https://gist.github.com/phuysmans/4f67a7fa1b0c6809a86f014694ac6c3a。
服务依赖
// TODO
docker compose 投票 app 练习
源码地址: https://github.com/dockersamples/example-voting-app
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