在 docker 中分离运行时，Python 应用程序不打印任何内容 [英] Python app does not print anything when running detached in docker

问题描述

我有一个在我的 dockerfile 中启动的 Python (2.7) 应用程序:

I have a Python (2.7) app which is started in my dockerfile:

CMD ["python","main.py"]

main.py 在启动时打印一些字符串，然后进入循环:

main.py prints some strings when it is started and goes into a loop afterwards:

print "App started"
while True:
    time.sleep(1)

只要我用 -it 标志启动容器，一切都会按预期进行:

As long as I start the container with the -it flag, everything works as expected:

$ docker run --name=myapp -it myappimage
> App started

我稍后可以通过日志看到相同的输出:

And I can see the same output via logs later:

$ docker logs myapp
> App started

如果我尝试使用 -d 标志运行同一个容器，容器似乎正常启动，但我看不到任何输出:

If I try to run the same container with the -d flag, the container seems to start normally, but I can't see any output:

$ docker run --name=myapp -d myappimage
> b82db1120fee5f92c80000f30f6bdc84e068bafa32738ab7adb47e641b19b4d1
$ docker logs myapp
$ (empty)

但是容器好像还在运行；

But the container still seems to run;

$ docker ps
Container Status ...
myapp     up 4 minutes ... 

Attach 也不显示任何内容:

Attach does not display anything either:

$ docker attach --sig-proxy=false myapp
(working, no output)

任何想法出了什么问题?在后台运行时，打印"的行为是否有所不同?

Any ideas whats going wrong? Does "print" behave differently when ran in background?

Docker 版本:

Client version: 1.5.0
Client API version: 1.17
Go version (client): go1.4.2
Git commit (client): a8a31ef
OS/Arch (client): linux/arm
Server version: 1.5.0
Server API version: 1.17
Go version (server): go1.4.2
Git commit (server): a8a31ef

推荐答案

我终于找到了在 Docker 中运行守护进程时查看 Python 输出的解决方案，感谢@ahmetalpbalkan 在 GitHub.自己在这里回答以供进一步参考:

Finally I found a solution to see Python output when running daemonized in Docker, thanks to @ahmetalpbalkan over at GitHub. Answering it here myself for further reference :

使用无缓冲输出

CMD ["python","-u","main.py"]

代替

CMD ["python","main.py"]

解决问题；您可以通过

docker logs myapp

现在！

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