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" |
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：
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