Docker Compose学习笔记

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简介

Docker Compose是一个用于定义和运行多容器Docker应用程序的工具。通过使用YAML文件来配置应用程序的服务，并使用docker-compose相关命令从配置中创建并启动所有服务。

使用Compose通常分为以下三部：

  1. 使用Dockerfile定义应用
  2. 使用docker-compose.yml定义服务
  3. 使用docker-compose up构建并启动应用

docker-compose.yml配置文件一般长这样：

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version: '3'
services:
  web:
    build: .
    ports:
    - "5000:5000"
    volumes:
    - .:/code
    - logvolume01:/var/log
    links:
    - redis
  redis:
    image: redis
volumes:
  logvolume01: {}

安装Docker Compose（Linux）

安装

  1. 运行下面的命令下载最新的Docker Compose

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    $ sudo curl -L "https://github.com/docker/compose/releases/download/1.22.0/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

  2. 为docker-compose命令添加可执行权限

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    $ sudo chmod +x /usr/local/bin/docker-compose

  3. 测试安装是否正确

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    $ docker-compose --version

卸载

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$ sudo rm /usr/local/bin/docker-compose

官方Starting Up

步骤一：设置

  1. 创建一个测试目录

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    $ mkdir composetest
    $ cd composetest

  2. 创建一个名为app.py的文件：

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    import time

    import redis
    from flask import Flask


    app = Flask(__name__)
    cache = redis.Redis(host='redis', port=6379)


    def get_hit_count():
        retries = 5
        while True:
            try:
                return cache.incr('hits')
            except redis.exceptions.ConnectionError as exc:
                if retries == 0:
                    raise exc
                retries -= 1
                time.sleep(0.5)


    @app.route('/')
    def hello():
        count = get_hit_count()
        return 'Hello World! I have been seen {} times.\n'.format(count)

    if __name__ == "__main__":
        app.run(host="0.0.0.0", debug=True)

上述例子中的redis是redis容器的在应用所属网络上的hostname，多个docker应用处于相同网络下时，通过hostname即可互相访问。

  1. 创建另一个名为requirements.txt的文件并添加以下内容：
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    flask
    redis

步骤二：创建Dockerfile

在这个步骤中，创建一个Dockerfile来构建Docker镜像。这个镜像包含Python环境和Python应用所需的所有依赖。

在项目目录中创建一个名为Dockerfile的文件并添加以下内容：

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FROM python:3.4-alpine
ADD . /code
WORKDIR /code
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

Dockerfile构建为镜像步骤：

  • 以Python 3.4-alpine镜像为基础构建一个镜像
  • 把当前目录.下的所有文件添加到镜像的/code目录中
  • 设置工作目录为/code
  • 运行安装Python依赖的命令
  • 设置容器默认启动命令为python app.py

步骤三：在Compose文件中定义服务

在项目目录中创建一个名为docker-compose.yml的文件并添加以下内容：

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version: '3'
services:
  web:
    build: .
    ports:
     - "5000:5000"
  redis:
    image: "redis:alpine"

上面这个Compose文件定义了两个服务，web和redis。

web服务：

  • 使用当前目录下的Dockerfile所构建的镜像
  • 在容器和宿主机中暴露5000端口，这是Flask web的默认端口

redis服务使用Docker Hub registry中的镜像构建。

步骤四：使用Compose构建和运行应用

  1. 在工程目录下执行docker-compose命令：

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    $ docker-compose up
    Building web
    Step 1/5 : FROM python:3.4-alpine
     ---> 73266cf72156
    Step 2/5 : ADD . /code
     ---> 93d41f61c2f8
    Step 3/5 : WORKDIR /code
     ---> Running in 74e35fbb2368
    Removing intermediate container 74e35fbb2368
     ---> 2dc16f910cce
    Step 4/5 : RUN pip install -r requirements.txt
     ---> Running in c82ef26c57ea
    Collecting flask (from -r requirements.txt (line 1))
      Downloading https://files.pythonhosted.org/packages/7f/e7/08578774ed4536d3242b14dacb4696386634607af824ea997202cd0edb4b/Flask-1.0.2-py2.py3-none-any.whl (91kB)
    Collecting redis (from -r requirements.txt (line 2))
      Downloading https://files.pythonhosted.org/packages/3b/f6/7a76333cf0b9251ecf49efff635015171843d9b977e4ffcf59f9c4428052/redis-2.10.6-py2.py3-none-any.whl (64kB)
    Collecting Jinja2>=2.10 (from flask->-r requirements.txt (line 1))
      Downloading https://files.pythonhosted.org/packages/7f/ff/ae64bacdfc95f27a016a7bed8e8686763ba4d277a78ca76f32659220a731/Jinja2-2.10-py2.py3-none-any.whl (126kB)
    Collecting click>=5.1 (from flask->-r requirements.txt (line 1))
      Downloading https://files.pythonhosted.org/packages/34/c1/8806f99713ddb993c5366c362b2f908f18269f8d792aff1abfd700775a77/click-6.7-py2.py3-none-any.whl (71kB)
    Collecting Werkzeug>=0.14 (from flask->-r requirements.txt (line 1))
      Downloading https://files.pythonhosted.org/packages/20/c4/12e3e56473e52375aa29c4764e70d1b8f3efa6682bef8d0aae04fe335243/Werkzeug-0.14.1-py2.py3-none-any.whl (322kB)
    Collecting itsdangerous>=0.24 (from flask->-r requirements.txt (line 1))
      Downloading https://files.pythonhosted.org/packages/dc/b4/a60bcdba945c00f6d608d8975131ab3f25b22f2bcfe1dab221165194b2d4/itsdangerous-0.24.tar.gz (46kB)
    Collecting MarkupSafe>=0.23 (from Jinja2>=2.10->flask->-r requirements.txt (line 1))
      Downloading https://files.pythonhosted.org/packages/4d/de/32d741db316d8fdb7680822dd37001ef7a448255de9699ab4bfcbdf4172b/MarkupSafe-1.0.tar.gz
    Building wheels for collected packages: itsdangerous, MarkupSafe
      Running setup.py bdist_wheel for itsdangerous: started
      Running setup.py bdist_wheel for itsdangerous: finished with status 'done'
      Stored in directory: /root/.cache/pip/wheels/2c/4a/61/5599631c1554768c6290b08c02c72d7317910374ca602ff1e5
      Running setup.py bdist_wheel for MarkupSafe: started
      Running setup.py bdist_wheel for MarkupSafe: finished with status 'done'
      Stored in directory: /root/.cache/pip/wheels/33/56/20/ebe49a5c612fffe1c5a632146b16596f9e64676768661e4e46
    Successfully built itsdangerous MarkupSafe
    Installing collected packages: MarkupSafe, Jinja2, click, Werkzeug, itsdangerous, flask, redis
    Successfully installed Jinja2-2.10 MarkupSafe-1.0 Werkzeug-0.14.1 click-6.7 flask-1.0.2 itsdangerous-0.24 redis-2.10.6
    Removing intermediate container c82ef26c57ea
     ---> b7c7a9180594
    Step 5/5 : CMD ["python", "app.py"]
     ---> Running in 874657b8b1c8
    Removing intermediate container 874657b8b1c8
     ---> 3398cf709b5c
    Successfully built 3398cf709b5c
    Successfully tagged composetest_web:latest
    WARNING: Image for service web was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
    composetest_redis_1 is up-to-date
    Creating composetest_web_1 ... done
    Attaching to composetest_redis_1, composetest_web_1
    redis_1  | 1:C 08 Sep 07:35:46.399 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
    redis_1  | 1:C 08 Sep 07:35:46.400 # Redis version=4.0.11, bits=64, commit=00000000, modified=0, pid=1, just started
    redis_1  | 1:C 08 Sep 07:35:46.400 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
    redis_1  | 1:M 08 Sep 07:35:46.405 * Running mode=standalone, port=6379.
    redis_1  | 1:M 08 Sep 07:35:46.405 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
    redis_1  | 1:M 08 Sep 07:35:46.405 # Server initialized
    redis_1  | 1:M 08 Sep 07:35:46.406 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
    redis_1  | 1:M 08 Sep 07:35:46.406 * Ready to accept connections
    redis_1  | 1:signal-handler (1536392231) Received SIGTERM scheduling shutdown...
    redis_1  | 1:M 08 Sep 07:37:11.181 # User requested shutdown...
    redis_1  | 1:M 08 Sep 07:37:11.182 * Saving the final RDB snapshot before exiting.
    redis_1  | 1:M 08 Sep 07:37:11.188 * DB saved on disk
    redis_1  | 1:M 08 Sep 07:37:11.188 # Redis is now ready to exit, bye bye...
    redis_1  | 1:C 08 Sep 07:37:14.802 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
    redis_1  | 1:C 08 Sep 07:37:14.802 # Redis version=4.0.11, bits=64, commit=00000000, modified=0, pid=1, just started
    redis_1  | 1:C 08 Sep 07:37:14.802 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
    redis_1  | 1:M 08 Sep 07:37:14.803 * Running mode=standalone, port=6379.
    redis_1  | 1:M 08 Sep 07:37:14.804 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
    redis_1  | 1:M 08 Sep 07:37:14.804 # Server initialized
    redis_1  | 1:M 08 Sep 07:37:14.804 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
    redis_1  | 1:M 08 Sep 07:37:14.804 * DB loaded from disk: 0.000 seconds
    redis_1  | 1:M 08 Sep 07:37:14.804 * Ready to accept connections
    web_1    |  * Serving Flask app "app" (lazy loading)
    web_1    |  * Environment: production
    web_1    |    WARNING: Do not use the development server in a production environment.
    web_1    |    Use a production WSGI server instead.
    web_1    |  * Debug mode: on
    web_1    |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
    web_1    |  * Restarting with stat
    web_1    |  * Debugger is active!
    web_1    |  * Debugger PIN: 303-324-532

  2. 在浏览器输入http://localhost:5000/查看应用是否运行正常。

  3. 在终端中输入docker images ls查看本地镜像：

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    $ docker image ls
    REPOSITORY                                 TAG                 IMAGE ID            CREATED             SIZE
    composetest_web                            latest              3398cf709b5c        5 minutes ago       78.4MB
    redis                                      alpine              162794862d37        12 hours ago        30MB
    python                                     3.4-alpine          73266cf72156        3 days ago          67.1MB

步骤五：修改Compose文件添加目录挂载

修改docker-compose.yml，给web服务添加一个目录挂载

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version: '3'
services:
  web:
    build: .
    ports:
     - "5000:5000"
    volumes:
     - .:/code
  redis:
    image: "redis:alpine"

volumes键值把当前目录挂载到容器内/code目录

步骤六：使用Compose重新构建和运行应用

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$ docker-compose up
Creating network "composetest_default" with the default driver
Creating composetest_web_1   ... done
Creating composetest_redis_1 ... done
Attaching to composetest_redis_1, composetest_web_1
redis_1  | 1:C 08 Sep 08:00:35.940 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
redis_1  | 1:C 08 Sep 08:00:35.940 # Redis version=4.0.11, bits=64, commit=00000000, modified=0, pid=1, just started
redis_1  | 1:C 08 Sep 08:00:35.940 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
redis_1  | 1:M 08 Sep 08:00:35.941 * Running mode=standalone, port=6379.
redis_1  | 1:M 08 Sep 08:00:35.941 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
redis_1  | 1:M 08 Sep 08:00:35.941 # Server initialized
redis_1  | 1:M 08 Sep 08:00:35.941 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
redis_1  | 1:M 08 Sep 08:00:35.941 * Ready to accept connections
web_1    |  * Serving Flask app "app" (lazy loading)
web_1    |  * Environment: production
web_1    |    WARNING: Do not use the development server in a production environment.
web_1    |    Use a production WSGI server instead.
web_1    |  * Debug mode: on
web_1    |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
web_1    |  * Restarting with stat
web_1    |  * Debugger is active!
web_1    |  * Debugger PIN: 741-610-125

步骤七：试一下其他指令

如果你想让你的服务在后台运行，给docker-compose up添加-d参数，并使用docker-compse ps查看当前的运行：

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$ docker-compose up -d
Creating network "composetest_default" with the default driver
Creating composetest_redis_1 ... done
Creating composetest_web_1   ... done
$ docker-compse ps
       Name                      Command               State           Ports
-------------------------------------------------------------------------------------
composetest_redis_1   docker-entrypoint.sh redis ...   Up      6379/tcp
composetest_web_1     python app.py                    Up      0.0.0.0:5000->5000/tcp

使用docker-compose run指令可以在容器内运行指令，例如查看web服务所在容器的环境变量：

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$ docker-compose run web env
PATH=/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=e0e26cbbba01
TERM=xterm
LANG=C.UTF-8
GPG_KEY=97FC712E4C024BBEA48A61ED3A5CA953F73C700D
PYTHON_VERSION=3.4.9
PYTHON_PIP_VERSION=18.0
HOME=/root

如果使用docker-compose up -d启动应用，可以使用docker-compose stop指令停止应用。

docker-compose down指令用来关闭所有，包括启动的容器，如果加上--volumes也会删除挂载的目录。

Compose文件第3版编写指南

Compose和Docker版本兼容性

Compose 文件格式 Docker Engine 版本
3.7 18.06.0+
3.6 18.02.0+
3.5 17.12.0+
3.4 17.09.0+
3.3 17.06.0+
3.2 17.04.0+
3.1 1.13.1+
3.0 1.13.0+
2.4 17.12.0+
2.3 17.06.0+
2.2 1.13.0+
2.1 1.12.0+
2.0 1.10.0+
1.0 1.9.1.+

Compose文件结构和示例

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version: "3"
services:

  redis:
    image: redis:alpine
    ports:
      - "6379"
    networks:
      - frontend
    deploy:
      replicas: 2
      update_config:
        parallelism: 2
        delay: 10s
      restart_policy:
        condition: on-failure

  db:
    image: postgres:9.4
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - backend
    deploy:
      placement:
        constraints: [node.role == manager]

  vote:
    image: dockersamples/examplevotingapp_vote:before
    ports:
      - "5000:80"
    networks:
      - frontend
    depends_on:
      - redis
    deploy:
      replicas: 2
      update_config:
        parallelism: 2
      restart_policy:
        condition: on-failure

  result:
    image: dockersamples/examplevotingapp_result:before
    ports:
      - "5001:80"
    networks:
      - backend
    depends_on:
      - db
    deploy:
      replicas: 1
      update_config:
        parallelism: 2
        delay: 10s
      restart_policy:
        condition: on-failure

  worker:
    image: dockersamples/examplevotingapp_worker
    networks:
      - frontend
      - backend
    deploy:
      mode: replicated
      replicas: 1
      labels: [APP=VOTING]
      restart_policy:
        condition: on-failure
        delay: 10s
        max_attempts: 3
        window: 120s
      placement:
        constraints: [node.role == manager]

  visualizer:
    image: dockersamples/visualizer:stable
    ports:
      - "8080:8080"
    stop_grace_period: 1m30s
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock"
    deploy:
      placement:
        constraints: [node.role == manager]

networks:
  frontend:
  backend:

volumes:
  db-data:

服务配置指南

Compose文件是一个定义服务、网络、挂载卷的YAML文件，默认的路径是./docker-compose.yml。

.yml或.yaml扩展名都是可以的

服务定义包含了应用于该服务所启动的各个容器的配置，就像将命令行参数传递给docker container create一样。同样，网络和卷定义类似于docker network create和docker volume create。

跟docker container create一样，配置项是在Dockerfile中指定的，如CMD, EXPOSE, VOLUME, ENV, 因为这些都是默认的，所以不需要再docker-compose.yml中再次指定。

配置中可以使用类似Bash的${VARIABLE}语法在值中使用环境变量。

build

构建时应用的配置。

build可以指定为包含构建上下文路径的字符串：

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version: '3'
services:
  webapp:
    build: ./dir

或者作为一个在context下面指定路径的对象以及可选的Dockerfile和args：

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version: '3'
services:
  webapp:
    build:
      context: ./dir
      dockerfile: Dockerfile-alternate
      args:
        buildno: 1

如果在build时指定image，Compose会按照image中指定的imageName和tag构建镜像：

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build: ./dir
image: webapp:1.0

上面的配置表示从./dir目录构建一个名为webapp标签为1.0的镜像。

该配置项在使用deploying a stack in swarm mode构建时会被忽略。

CONTEXT

包含Dockerfile的目录的路径，或者是git仓库的url。

当提供的值是相对路径时，则表示相对于Compose文件的位置。此目录也是发送到Docker守护程序的构建上下文。

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build:
  context: ./dir

DOCKERFILE

Compose使用备用Dockerfile来构建，同时还必须指定构建路径。

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build:
  context: .
  dockerfile: Dockerfile-alternate

ARGS

添加构建参数，这些参数只能在构建过程中访问。

首先，在Dockerfile中指定参数：

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ARG buildno
ARG gitcommithash

RUN echo "Build number: $buildno"
RUN echo "Based on commit: $gitcommithash"

然后在构建键下指定参数。可以传递映射或列表：

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build:
  context: .
  args:
    buildno: 1
    gitcommithash: cdc3b19

build:
  context: .
  args:
    - buildno=1
    - gitcommithash=cdc3b19

参数也可以省略，在这种情况下，构建时的值是运行Compose的环境中的值。

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args:
  - buildno
  - gitcommithash

YAML中的布尔值(true, false, yes, no, on, off) 必须用引号括起来，以便解析器将它们解释为字符串。

CACHE_FROM

v3.2新增

设置一些引擎用于缓存解决方案的镜像：

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build:
  context: .
  cache_from:
    - alpine:latest
    - corp/web_app:3.14

LABELS

v3.3新增

使用Docker标签将元数据添加到生成的镜像中。可以使用数组或字典。

建议使用反向DNS表示法来防止标签与其他软件使用的标签冲突。

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build:
  context: .
  labels:
    com.example.description: "Accounting webapp"
    com.example.department: "Finance"
    com.example.label-with-empty-value: ""


build:
  context: .
  labels:
    - "com.example.description=Accounting webapp"
    - "com.example.department=Finance"
    - "com.example.label-with-empty-value"

SHM_SIZE

v3.5新增

为此构建的容器设置/dev/shm分区的大小。

指定表示字节数的整数值：

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build:
  context: .
  shm_size: 10000000

或表示字节值的字符串：

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build:
  context: .
  shm_size: '2gb'

TARGET

v3.4新增

根据Dockerfile中的定义构建指定的阶段：

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build:
    context: .
    target: prod

cap_add, cap_drop

添加或删除容器功能：

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cap_add:
  - ALL

cap_drop:
  - NET_ADMIN
  - SYS_ADMIN

该配置项在使用deploying a stack in swarm mode构建时会被忽略。

command

覆盖默认命令：

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command: bundle exec thin -p 3000

该命令也可以是一个列表，方式类似于dockerfile：

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command: ["bundle", "exec", "thin", "-p", "3000"]