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‫In this lecture, we're going to talk about bind mounting and persistent data in those mounts. The

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‫requirements are really that you just know about container management and how to run containers.

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‫Let's jump in. Let's talk about bind mounts. They're actually pretty cool.

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‫When I first learned about them, it sort of gave me an aha of how I could use Docker easily for local

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‫development.

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‫Really, a bind mount is just a mapping of the host files, or directories, into a container file or

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‫directory. You can do just that.

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‫You can either specify a directory or just a single file. In the background,

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‫it's basically just having the two locations point to the same physical locations on disk.

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‫Again, this actually skips the UFS like the other volumes do so that it's not going to wipe out your

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‫host location when you delete the container.

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‫If there are any files in the container that you map the host files to, the host files win. It

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‫doesn't actually delete the files in the container that it overwrote because it's not really overwriting

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‫anything in the container.

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‫It's just there while the bind mount exists.

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‫The minute you don't need the bind mount any more and you re-run the container without it, you would

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‫actually see the underlying data that was there before. Because bind mounts are usually host specific,

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‫they need specific data to be on the hard drive of the host in order to work.

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‫You can't specify them in a Dockerfile.

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‫You have to use them at runtime when you use the docker container run command. You can see the format

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‫here.

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‫It's really the -v that we used before, only on the left side of the colon,

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‫we're actually putting in a full path rather than just a name.

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‫And the way the Docker actually can tell the difference between the named volume, like we did a while ago,

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‫and the bind mount, is the bind mount starts with a forward slash.

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‫On Windows, you'll notice that it's a two forward slashes and then the drive letter, and then your

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‫path.

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‫As long as you have the left colon and right sides, you can really map anything you want from the

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‫host into the container, and you can also specify things like read-only.

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‫Where this really comes to shine is with development and running services inside your container

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‫that are accessing files you're using on your host or changing.

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‫Let's do that with Nginx.

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‫If you go to the root of our repository for this course, and then we go into the Dockerfile sample

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‫2 directory. Now we were in here earlier.

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‫If you remember, there's two files. This is for Nginx, right?

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‫If we look at the Dockerfile real quick, it's pretty simple. It's just specifying a working directory

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‫and then copying an index file into that directory.

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‫There's no volumes here.

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‫A bind mount doesn't require a volume to work, although one could certainly be there.

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‫The host always wins, remember? So, when we're doing a docker container run, then we do a

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‫-d...let's name it nginx.

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‫Let's give it the port 8080 like before.

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‫Then we're going to give it the volume this time. And I need to tell it my current working directory

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‫is going to be actually mounted into that working directory in the container. Because my index file is

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‫here in this folder,

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‫I want it to be in the container so I can edit it here, and it is seen live in the container.

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‫So it will make sense in a second.

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‫Here's a quick little tip. Instead of me having to figure out my whole path and type the whole thing

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‫in, you can use pwd here like so.

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‫Which is a shell shortcut that says, 'print out the working directory and replace this command with that

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‫path.'

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‫Then we're just going to use the same working directory from the Dockerfile there, and then we're going to

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‫specify the Nginx image.

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‫What I'm going to do, real quick, is I'm actually going to open up another terminal window so we can

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‫do two things at once.

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‫You don't really need to do this.

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‫Basically, we're just going to edit the file on our host, and then I'm going to be in the container and

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‫see what's happening.

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‫So just to make sure it's working,

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‫let's go to localhost.

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‫OK, so this isn't the default Nginx HTML file.

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‫And we used the regular Nginx image.

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‫We didn't actually use the custom one from this directory.

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‫We just used a stock image. To prove that point, we can actually do that same, exact command again but

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‫take out the -v, and I'll run it on port 8080 instead. And I'll call this one nginx2.

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‫If I go over to my browser and go to localhost 8080, that's the default nginx index.html

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‫file.

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‫This one is the custom one that we have living in this directory.

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‫So, already we can see that it mapped it correctly.

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‫If I open up another tab here and get a command line in the container.

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‫Then go to that directory.

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‫You'll notice that we can actually see the Dockerfile because we map the whole directory.

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‫If over on the left, if we actually made a new file and I can just use that Linux touch command here

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‫to create a new file. Then over on the right...oops...just keep forgetting that...ls -al, and you'll

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‫see that in your file.

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‫Hopefully you understand what's going on here, that both these locations are the same location.

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‫And if I echoed something into that testme file,

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‫and then...

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‫there you go.

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‫Our nginx is able to see the changes because it's just a normal file path in the container,

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‫and those files are on the host.

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‫If I was to delete them in the container, they would be deleted on the host because it is the same

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‫file.

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‫This is when I usually get a developer to get their mind thinking about all of their development environments

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‫that they have that are this complicated setup. Maybe they're using Vagrant, or some other manual method

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‫of setting up their perfect environment, and they can start to see how this could make that so much simpler.

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‫Because I didn't have to do any complicated setup on my Mac, I just ran a container.

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‫I used the -v command with the mount, and now my code, on my host, can be edited on my host.

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‫And I really never need to go into the shell of the container.

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‫Usually, you can just run the container and look at its logs to see if there's any errors while you're

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‫coding.

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‫Of course, this is a simple example with Nginx. Later on, we're actually going to have specific

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‫examples of different development environments for local development and containers.