docker compose 服务依赖和健康检查#
Dockerfile healthcheck https://docs.docker.com/engine/reference/builder/#healthcheck
docker compose 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
PS C:\Users\Peng Xiao\code-demo\compose-env\flask> dir
目录: C:\Users\Peng Xiao\code-demo\compose-env\flask
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---- 2021/7/13 15:52 448 app.py
-a---- 2021/7/14 0:32 471 Dockerfile
PS C:\Users\Peng Xiao\code-demo\compose-env\flask> more .\app.py
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"
PS C:\Users\Peng Xiao\code-demo\compose-env\flask> more .\Dockerfile
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
docker-compose 健康检查#
示例代码下载(flask healthcheck) 本节源码
示例代码下载(flask + redis healthcheck) 本节源码
一个healthcheck不错的例子 https://gist.github.com/phuysmans/4f67a7fa1b0c6809a86f014694ac6c3a