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So that were volumes and bind mounts.

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Here's a quick overview, since I know it's a lot to digest

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and easy to mix up these concepts.

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You basically have these three ways

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of using the dot v option when you use docker run.

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And, this first example would create

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an anonymous volume since you don't assign any name.

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The second example would create a named volume

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since you do assign a name.

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And in the third example, the name is actually

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an absolute path to a folder on your host machine

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and therefore this is then a bind mount.

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It's actually as easy as that.

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Now when it comes to the different features

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these different concepts have,

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I've got another comparison for you.

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With anonymous volumes, you create a volume

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which is kind of attached to a container.

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It's removed if the container is removed.

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It survives container shut down and restart,

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but if it's removed, it's gone and therefore

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if you use the dash dash rm

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when you ran the container,

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of course the volume is all gone when you stop the container

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because stopping then basically also means

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removing the container.

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Therefore, since it is removed when the container

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is removed, you can't use anonymous volumes

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to share data across containers.

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And you also can't use it to save data across container

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destruction and recreation as you saw.

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Anonymous volumes are not useful for that.

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But anonymous volumes either created

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with the volume instruction in the dockerfile

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or created with dash v, like this,

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can be useful for locking in certain data

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which already exists in the container.

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They can be useful for avoiding

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that this data then gets overwritten by another module.

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And that's something where anonymous volumes

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can save the day.

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In addition, anonymous volumes also still create

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a counterpart, a folder, on your host machine.

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Of course that's removed when the container's removed,

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but that exists as long as the container is running.

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And that of course means that docker

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doesn't have to store all the data inside

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of the container and doesn't have

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to manage all the data inside

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of this container read write layer.

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But that instead it can outsource certain data

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to your host machine file system.

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And this can also help with performance and efficiency.

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So that's why anonymous modules can be worth a closer look.

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And in this example,

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we could consider creating another anonymous volume,

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maybe inside of the docker file

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to mix things up for the temp folder.

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It's okay if we lose that folder

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when the container is removed,

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but for the reasons I just mentioned,

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for example for tiny performance improvements,

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it can be worth mapping this temp folder

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to an anonymous volume so the data managed in there

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is not managed in the docker container anymore,

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but actually well outsourced

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to the host file system, you could say.

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That could be useful and therefore

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it is something we can do here for sure.

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Obviously very useful, are named volumes.

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Named volumes can not be created in the dockerfile,

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but instead you create them with the dash v instruction

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when you run a container.

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They are named because you assign a name

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in front of the colon.

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Now the great thing about named volumes

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is that they're created in general.

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They're not tied to any specific container.

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They do survive container shut down

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and also the removal of containers.

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If you want to remove a named volume,

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you can still do that, but you have to do it

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with a separate command built into the Docker CLI.

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00:04:07,100 --> 00:04:08,763
We'll have a look at that later.

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Now since they survived container removal,

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you can use named volumes

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to share data across multiple containers,

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Something we didn't do in this module,

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but of course you could do that.

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You could mount one of the same named module

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to multiple different containers,

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and hence the data in there

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could be shared between containers.

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And you can also use them

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to store data across container shutdowns and removals.

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That is what we did in this module.

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And then we had bind mounts.

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Bind mounts serve a different purpose.

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00:04:46,610 --> 00:04:51,200
Here we know where data is stored on the host machine.

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Bind mounts are also not tied to one specific container.

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00:04:55,040 --> 00:04:57,400
You can attach them to multiple containers

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00:04:57,400 --> 00:05:01,350
and they do survive container shutdown and removal.

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00:05:01,350 --> 00:05:04,830
If you want to clear the data of a bind mount,

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00:05:04,830 --> 00:05:08,200
you actually have to delete it on your host machine.

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00:05:08,200 --> 00:05:10,850
So here I would have to delete all the content here

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in my project to also remove it in the container.

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You can't delete it with a docker command.

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And that makes a lot of sense,

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because it is a folder on your system after all

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and you don't want to accidentally delete this somehow.

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Now of course you can share them across containers

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and you can also reuse them on one

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of the same container across restarts.

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This also works.

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And these are the three main ways we have

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for managing data inside of a container.

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I hope I could make it clear what the differences are

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and when you use which.

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And of course it should be needless to say

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that throughout this course,

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we'll also have plenty of other examples

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where it shows this.