Instructor Demo: Basic Volume Usage

In this demo, we'll illustrate:

Creating, updating, destroying, and mounting docker named volumes
How volumes interact with a container's layered filesystem
Usecases for mounting host directories into a container

Using Named Volumes

Create a volume, and inspect its metadata:

PS: node-0 Administrator> docker volume create demovol
PS: node-0 Administrator> docker volume inspect demovol

[
    {
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "C:\\ProgramData\\docker\\volumes\\demovol\\_data",
        "Name": "demovol",
        "Options": {},
        "Scope": "local"
    }
]

We can see that by default, named volumes are created under C:\\ProgramData\\docker\\volumes\\<volume name>\\_data.

Run a container that mounts this volume, and list the filesystem therein:

PS: node-0 Administrator> docker container run `
    -it -v demovol:C:\demo microsoft/nanoserver powershell
PS C:\> ls

    Directory: C:\

Mode                LastWriteTime         Length Name
----                -------------         ------ ----
d----l        8/26/2018  12:10 AM                demo
d-----        8/26/2018  12:11 AM                Program Files
d-----        7/16/2016  12:09 PM                Program Files (x86)
d-r---        8/26/2018  12:11 AM                Users
d-----        8/26/2018  12:11 AM                Windows
-a----       11/20/2016  11:32 AM           1894 License.txt

The demo directory is created as the mountpoint for our volume, as specified in the flag -v demovol:C:\demo.

Put a file in this volume:

PS C:\> echo 'dummy file' > C:\demo\mydata.dat

Exit the container, and list the contents of your volume on the host:
```
PS: node-0 Administrator> ls C:\\ProgramData\\docker\\volumes\\demovol\\_data
```
You'll see your mydata.dat file present at this point in the host's filesystem. Delete the container:
```
PS: node-0 Administrator> docker container rm -f <container ID>
```
The volume and its contents will still be present on the host.

Start a new container mounting the same volume, and show that the old data is present in your new container:

PS: node-0 Administrator> docker container run `
    -it -v demovol:C:\demo microsoft/nanoserver powershell
PS C:\> cat C:\demo\mydata.dat

Exit this container, and inspect its mount metadata:

PS: node-0 Administrator> docker container inspect <container ID>

    "Mounts": [
        {
            "Type": "volume",
            "Name": "demovol",
            "Source": "C:\\ProgramData\\docker\\volumes\\demovol\\_data",
            "Destination": "c:\\demo",
            "Driver": "local",
            "Mode": "",
            "RW": true,
            "Propagation": ""
        }
    ],

Here we can see the volumes and host mountpoints for everything mounted into this container.

Clean up by removing that volume:
```
PS: node-0 Administrator> docker volume rm demovol
```
You will get an error saying the volume is in use - docker will not delete a volume mounted to any container (even a stopped container) in this way. Remove the offending container first, then remove the volume again.

Mounting Host Paths

In a fresh directory myweb, make a Dockerfile to make a simple containerization of nginx:

FROM microsoft/windowsservercore
RUN ["powershell", "wget", "http://nginx.org/download/nginx-1.11.6.zip", \
     "-UseBasicParsing", "-OutFile", "c:\\nginx.zip"]
RUN ["powershell", "Expand-Archive", "c:\\nginx.zip", "-Dest", "c:\\nginx"]
WORKDIR c:\\nginx\\nginx-1.11.6
ENTRYPOINT ["powershell", ".\\nginx.exe"]

Build this image, and use it to start a container that serves the default nginx landing page:
```
PS: node-0 myweb> docker image build -t nginx .
PS: node-0 myweb> docker container run -d -p 5000:80 nginx
```
Visit the landing page at <node-0 public IP>:5000 to confirm everything is working, then remove this container.

Create some custom HTML for your new website:

PS: node-0 myweb> echo "<h1>Hello Wrld</h1>" > index.html

The HTML served by nginx is found in the container's filesystem at C:\nginx\nginx-1.11.6\html. Attempt to mount your myweb directory at this path:
```
PS: node-0 myweb> docker container run -d -p 5000:80 `
    -v C:\Users\Administrator\myweb:C:\nginx\nginx-1.11.6\html `
    nginx
```
The container startup fails, since the C:\nginx\nginx-1.11.6\html directory isn't empty.
Modify your Dockerfile to remove the default content in this directory by adding one more line at the end:
```
RUN ["powershell", "Remove-Item", "C:\\nginx\\nginx-1.11.6\\html\\*"]
```
Rebuild your nginx image.
Launch an nginx container again based on this new nginx image, and mount in your custom html:
```
PS: node-0 myweb> docker container run -d -p 5000:80 `
    -v C:\Users\Administrator\myweb:C:\nginx\nginx-1.11.6\html `
    nginx
```
Visit your webpage <node 0 public IP>:5000; you should be able to see your custom webpage.
There's a typo in your custom html. Fix the spelling of 'world' in your HTML, and refresh the webpage; the content served by nginx gets updated without having to restart or replace the nginx container.

Conclusion

In this demo, we saw two key points about volumes: first, they persist and provision files beyond the lifecycle of any individual container. Second, we saw that manipulating files on the host that have been mounted into a container immediately propagates those changes to the running container; this is a popular technique for developers who containerize their running environment, and mount in their in-development code so they can edit their code using the tools on their host machine that they are familiar with, and have those changes immediately available inside a running container without having to restart or rebuild anything.