docker - 关于Docker文件系统的奥秘

Question

刚刚开始使用docker。我已经创建了一个镜像，启动了一个容器，但是当我在容器中写入文件时，它会显示在本地磁盘上。我很奇怪为什么会这样，如果那样，我怎么可能运行图像的许多实例。

这是我的工作

docker container ls
 CONTAINER ID        IMAGE               COMMAND                  
 CREATED             STATUS              PORTS                    NAMES
 5bf6d45b4f79        docker_1_web        "bundle exec rails s…"   About an hour ago   Up About an hour    0.0.0.0:3000->3000/tcp   docker_1_web_1
 d5d0991da014        postgres            "docker-entrypoint.s…"   About an hour ago   Up About an hour    5432/tcp                 docker_1_db_1

然后

docker exec -it 5bf6d45b4f79 echo "hello" > temp.txt

和

docker exec -it 5bf6d45b4f79 cat temp.txt
hello

但是在我的Mac命令行中的本地磁盘上

cat temp.txt
hello

在我的Mac命令行上

echo "goodbye" >> temp.txt
cat temp.txt
hello
goodbye

然后在容器中

docker exec -it 5bf6d45b4f79 cat temp.txt
hello
goodbye

h!怎么来的？我以为Docker容器写入了自己的文件系统。所以我完全迷惑了。

这也意味着我无法运行图像的多个实例，因为它们都将写入相同的文件。

Answer 1

让我们澄清一下:

When you do:

docker exec -it 5bf6d45b4f79 echo "hello" > temp.txt
docker exec -it 5bf6d45b4f79 cat temp.txt
hello

You're executing echo "hello" in your container but stdoutput is stored in your host. So, is normal that you see temp.txt in your host.

如果要在容器中保存temp.txt，请尝试:

docker exec -it 5bf6d45b4f79 bash -c "echo 'hello' > temp.txt"

并且temp.txt将在您的容器workdir上生成。

When you do:

But on my local disk in my Mac command line

cat temp.txt hello Followed on my Mac command line by

echo "goodbye" >> temp.txt cat temp.txt hello goodbye 

And then in the container

docker exec -it 5bf6d45b4f79 cat temp.txt hello goodbye

You're sharing temp.txt, maybe it's generated in a docker volume shared between host and docker