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So now we learn about volumes,

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and specifically named volumes are useful.

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Anonymous volumes, I would say,

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their use is not entirely clear yet.

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I'll come back to those.

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But I actually now wanna dive into bind mounts first,

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before we have a look at anonymous volumes again.

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Because bind mounts, can help us with

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a different kind of problem we might be facing.

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And here is the kind of problem we might be facing.

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Whenever we change anything in our source code,

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be that in the server JS file, or in any HTML file here,

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those changes are not reflected in the running container

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unless we rebuild the image.

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I mean, we do have a running application here.

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And if I go back to localhost 3000,

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it's actually the feedback HTML file which is loaded.

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But if I add, please here, after your feedback,

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and I save this file, if I reload here,

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we don't see please on the page.

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And it should be clear why this is happening.

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I emphasized this a lot in the last module and this module,

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we only copy a snapshot off this folder,

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into the Docker image when it's created,

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and subsequent changes to anything in that folder,

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will therefore not be reflected in the image,

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and therefore also not in the container.

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But of course, during development, if we're using Docker,

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it would be pretty important to us,

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that such changes are reflected.

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Because otherwise, we always have

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to rebuild the entire image and restart a container,

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whenever we change anything.

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And of course, during development, we tend to change a lot.

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So restarting everything all the time is pretty cumbersome.

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That's where bind mounts can help us.

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Bind mounts have some similarities with volumes,

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but there is one key difference.

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Where volumes are managed by Docker,

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and we don't really know where

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on our host machine file system they are.

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For bind mounts, we do know it.

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Because for bind mounts, we, as a developer,

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set the path to which the container internal path

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should be mapped on our host machine.

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So here, we're fully aware off the path

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on our localhost machine.

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And since that is the case,

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and containers cannot just write to volumes,

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but also read from there,

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of course we could put our source code

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into such a bind mount.

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And if we do that, we could then make sure that

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the container is aware of that,

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and that the source code is actually not used

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from that copied in snapshot,

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but instead from that bind mount.

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So from that connection to some folder on our host machine.

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And therefore the container would always have access

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to the latest code.

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And not just to the snapshot we put into our image here

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when it was created at the beginning.

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So bind mounts are therefore perfect,

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for persistent and editable data.

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And that's the difference to normal volumes.

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A named volume can help us with persistent data,

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but editing is not really possible, since we don't know

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where it's stored on our host machine.

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So how can we then add such a bind mount?

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Again, it's not something we can do

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from inside the Docker file.

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Because it's actually specific to a container which you run,

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not to the image, it doesn't affect the image,

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it just affects the container.

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And therefore, we have to set up a bind mount

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from inside the terminal when we run our container.

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So for that, first of all, I'll stop.

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I'll stop my currently running container

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with Docker stop feedback app.

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And once this is stopped, I will rerun it,

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I will create a new container in the same way,

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by using Docker run.

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But now I'll add more than one volume,

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not just this one named volume, but a second volume,

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simply by again adding dash V.

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And now there is a line break,

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but it's dash V and then a whitespace.

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So a blank.

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And then again, a volume as we added it before.

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But now here's the key difference.

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The folder to which I wanna map it inside of the container,

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is just slash app, of course.

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So just slash app, because I'm also copying

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all my source code into just slash app here.

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So I wanna control the entire app folder now.

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But, and that's the difference.

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The name which I now assign in front of the colon,

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is now not app or anything like that.

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Instead it is a path to the folder on my host machine,

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where I have all the code, all the content,

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that should go into this mapped folder.

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And this must be an absolute path here, not a relative one.

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You can get such a path here in Visual Studio Code

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by right clicking on server JS, for example,

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and choosing copy path.

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Choose that, and added in front of the colon.

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Yes, it's quite long, but that is what we need.

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Make sure you remove the file at the end though,

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it should just be the path to your project folder.

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So your project folder name should be the last thing here.

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In this case, at least, you can also bind a single file,

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in case you just wanna share a single file with a container,

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you can bind a file to a file.

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But here when I wanna bind to a folder,

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and therefore I wanna bind a complete folder

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on my hosting machine to this app folder in the container.

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That's why we're removing the file name at the end.

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Because I don't just wanna share the file,

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I wanna share the complete folder.

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You might also wanna consider putting this into quotes,

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this entire statement here.

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So your absolute path, the colon, and the MapPath,

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to ensure that it doesn't break in case your path

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includes special characters or whitespace.

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Mine doesn't, except for the slashes, which are okay.

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But if your path has some blanks in it

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or anything like that, simply wrap everything here,

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the entire volume mapping with quotes.

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Now, one important note about bind mounts

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and mounting folders, which you know, into containers.

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You should make sure that Docker has access to the folder

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which you're sharing as a bind mount.

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And you can do this by accessing the preferences of Docker,

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by using that running Docker service,

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this Docker process you started.

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And there, make sure that under Resources file sharing,

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your folder which you are sharing right now, is listed here.

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It doesn't have to be the full folder,

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but it should be a parent folder,

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of the folder you're sharing.

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If you don't have this file sharing area under Resources,

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you are most likely on windows

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and their you don't have this option,

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you don't have this area in the settings.

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If you are running Docker with help of the WSL integration,

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you might remember the setup lecture,

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from the first course section.

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Well, if that option is missing, that's no problem,

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it's missing because you won't have any problems

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with file sharing anyways, with the setup you're using,

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so you're fine.

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Now if you should be using Docker Toolbox to run Docker,

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then by default your users folder will be shared,

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and attached you find a link to an article

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which explains how you can share other folders as well.

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So that is what you should do then,

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if you are using Docker Toolbox to ensure that,

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Docker is able to really write to your

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localhost system machine for the given folder

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you wanna use as a volume in your container.

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So the attached link is for you,

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if you are using Docker Toolbox.

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So in my case, for example, the project I'm sharing

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is in some sub folder of my users directory.

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And that will be accessible by Docker,

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because it's listed here, under file sharing Resources.

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Now if your project is in some folder,

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which is not a sub folder of one of the resources

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specified here, you should make sure

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that you add your project folder,

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or a parent folder of it, even better,

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as a shareable resource in this list

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in your Docker preferences, that's important.

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And if we now hit enter, this starts the container again.

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And now our entire folders here,

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will be mounted as a volume, into the app folder,

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inside of the container.

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Nonetheless, you'll notice if you reload, that it crashes.

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And if we inspect our running

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and shutdown containers thereafter,

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we see this container is nowhere to be found.

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And we don't find it in the closed containers,

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in the stopped containers,

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because we remove all containers which are shut down.

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But this of course also means that,

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it seems to shut down immediately.

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So something seems to be very wrong here.

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And to find out what's wrong, I'll restart it again.

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But now without dash, dash RM,

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to not automatically remove it

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when it shuts down.

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And thereafter we see it here, under stopped containers.

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And we can now use Docker logs, to look into our container,

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to see the error that was thrown.

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And we see that the problem is,

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that it fails to find the module Express.

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And that simply means that our node code

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doesn't even start executing,

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because an important dependency is missing.

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Now up to this point, it always worked, of course.

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And after all, we are installing all dependencies

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with the npm install instruction in the Docker file.

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So why is it missing now?

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Well, that has something to do with

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our newly added bind mount.

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With this bind mount that binds our entire project folder

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to the app folder.

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And we'll see what's wrong and how to solve the problem,

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in the next lecture.