Docker Compose

简介：

Compose 是用于定义和运行多容器 Docker 应用程序的工具。通过 Compose，您可以使用 YML 文件来配置应用程序需要的所有服务。然后，使用一个命令，就可以从 YML 文件配置中创建并启动所有服务。一键配置所有的服务，启动所有服务；

使用步骤：

第一步、下载Docker Compose

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curl -L https://get.daocloud.io/docker/compose/releases/download/1.24.0/docker-compose-`uname -s`-`uname -m` > /usr/local/bin/docker-compose

第二步、更改文件权限

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

第三步、按照官网准备文件

  1. Create a directory for the project:

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    $ mkdir composetest
    $ cd composetest

  2. Create a file called app.py in your project directory and paste this in:

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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)

    In this example, redis is the hostname of the redis container on the application’s network. We use the default port for Redis, 6379.

    Handling transient errors

    Note the way the get_hit_count function is written. This basic retry loop lets us attempt our request multiple times if the redis service is not available. This is useful at startup while the application comes online, but also makes our application more resilient if the Redis service needs to be restarted anytime during the app’s lifetime. In a cluster, this also helps handling momentary connection drops between nodes.

  3. Create another file called requirements.txt in your project directory and paste this in:

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    flask
    redis

Step 2: Create a Dockerfile

In this step, you write a Dockerfile that builds a Docker image. The image contains all the dependencies the Python application requires, including Python itself.

In your project directory, create a file named Dockerfile and paste the following:

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FROM python:3.7-alpine
WORKDIR /code
ENV FLASK_APP=app.py
ENV FLASK_RUN_HOST=0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
EXPOSE 5000
COPY . .
CMD ["flask", "run"]

This tells Docker to:

  • Build an image starting with the Python 3.7 image.
  • Set the working directory to /code.
  • Set environment variables used by the flask command.
  • Install gcc and other dependencies
  • Copy requirements.txt and install the Python dependencies.
  • Add metadata to the image to describe that the container is listening on port 5000
  • Copy the current directory . in the project to the workdir . in the image.
  • Set the default command for the container to flask run.

For more information on how to write Dockerfiles, see the Docker user guide and the Dockerfile reference.

Step 3: Define services in a Compose file

Create a file called docker-compose.yml in your project directory and paste the following:

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version: "3.8"
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"