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‫This lecture is going to be all about adding image building into your Compose files so that it automatically

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‫ensures that you have an image ready to go

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‫when you're running compose commands. Like other lecturers in this section, you really need to have a good

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‫sense of Docker container and Docker image command line functionality.

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‫Another thing that Compose can do for you is build your images at runtime. It'll actually look in the

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‫cache for images, and if it has build options in it, it will build that image when you use the up command.

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‫It won't build the image every single time.

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‫It'll only build it if it doesn't find it.

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‫You'll need to either use the docker compose build to rebuild your images if you change them,

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‫or you can use docker compose up --build.

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‫We'll actually see that in a minute.

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‫This is really great for when you're using Compose locally and you have images you want to build. Maybe

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‫you don't want to use volume mount. You actually want to copy files in, or something, into the image.

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‫Your build command might be fairly complex. It might have some custom environment variables or build

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‫arguments.

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‫By the way, build arguments, we haven't talked about. That's really just environment variables that

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‫are available only during builds. You can look at the docs. docker.com documentation on Dockerfiles

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‫and it'll talk about build arguments in depth.

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‫Here, we're going to look at an example of how you might use that locally.

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‫I'm in the compose sample 3 directory. You can see here I have a pre-built Docker Compose file

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‫here.

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‫I have actually a Dockerfile called nginx.Dockerfile. Then a similar nginx config to what

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‫we had earlier, where we're actually using Nginx as a reverse proxy for our website.

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‫If we go into the Docker Compose, you can see how I've architected this solution.

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‫I've actually got two services.

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‫One is the Nginx proxy like before, and one is the Apache web server like before.

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‫But a couple of things are different.

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‫Instead of me specifying the default image for Nginx, I'm actually building a custom one.

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‫You can see here that I've actually given it some arguments where I'm telling it that the Dockerfile

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‫it needs to use is a specially named Dockerfile.

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‫I want it to build that Dockerfile in this current directory that it's in. I want it to name that image

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‫when it builds it, nginx

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‫-custom. It's going to store that in my local cache. Then down there at the bottom, we have a web

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‫server running Apache.

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‫What I've done here is I've actually mounted some HTML source files that I have into the Apache server.

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‫So the scenario here is maybe I'm a web developer,

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‫I have a static website here,

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‫underneath this HTML directory that I don't really need to worry about too much.

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‫It's just using a little bootstrap template.

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‫I'm going to be editing on that locally, in my editor here, but I know when I go to production with this,

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‫it's actually going to be sitting behind an Nginx proxy.

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‫So, I want to emulate that production environment as much as possible, locally, just to make sure that

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‫I've weeded out any bugs or any problems. In this case,

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‫I want this Nginx, and I know that this Nginx config is the one they're going to use on the

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‫production server, so that I'm just going to use that here.

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‫This is actually the same Nginx config as before.

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‫When I run the docker compose up command, it's going to first check for the name of this image in

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‫my cache. If it doesn't find it, then it's going to use these build commands here to look up the Dockerfile

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‫and then build my image. You can see from this Dockerfile, it's pretty simple actually.

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‫It's just going to use a specific version of Nginx and then it's just going to copy a file in.

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‫It's going to get the rest of its information from that Nginx config from Docker Hub and then

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‫it's going to copy in my Nginx config.

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‫If you remember in a previous example, we actually did a bind mount to get this Nginx config in

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‫through our compose file.

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‫In this case, we're just wanting it to build the whole image.

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‫We don't really need to be changing this proxy config, so I don't really need to mount it so that I can

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‫change it all the time.

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‫I just want it to run. Right? So, I'm going to build it. Let it sit in the image cache. Once it's built the

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‫first time, it won't need to be really rebuilt very often.

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‫So I'm just going to leave there.

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‫Then when I'm editing and developing on my website, I'm going to have this configuration so I can

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‫do live edits. If we go back over here and I do a docker compose up,

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‫let's step through what happened.

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‫It first created the network.

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‫That's a normal thing. It does that.

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‫Then it actually is seen that the proxy service doesn't have the image it's looking for. So it's

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‫going to build that.

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‫So it's pulling out the Dockerfile and building it just like it would do a normal docker build command.

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‫Then it's giving me this helpful tip to let me know that it built the image this time because it

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‫couldn't find it.

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‫But in the future, if I need to change that image, I'm going to need to use the docker compose build

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‫or the docker compose up --build commands. Now that it's got the image,

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‫it can actually create the containers. Then it's starting my web server and my proxy server.

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‫If everything worked correctly, I should be able to get a localhost. It pulled up my default template

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‫here, which is a bootstrap template actually.

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‫It looks like everything works.

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‫Actually, I go over here and I can see all my logs coming up and obviously there's a lots of assets. There's

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‫a log entry for each one and it's going to go through the proxy and through the web server.

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‫Because I've bind mounted that directory for editing, I can actually go back into my editor. As

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‫a web developer, I could go in and maybe, you know, edit something on the website. Maybe I'll go into the start

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‫bootstrap title, which should be this little title up top here.

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‫I'll just save that file. Then if I refresh, my website's updated because of that bind mount again.

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‫This is a great example of a very common developer setup where you need to build some custom images

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‫locally.

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‫You also need to mount some files into your application so that you can edit them at runtime.

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‫And, of course, if this needed to be a database-backed application, I would just add a third service down

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‫here for the database server. Then, I'll go back and do my cleanup.

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‫You'll notice that, by default, it won't actually delete that image.

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‫You'll notice up at the top here, we have the nginx custom that it built. But there is a docker compose

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‫down command.

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‫If you look at the help, you see that there's an rmi option that actually removes images it may have

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‫built or it may be using.

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‫There's this actual option here says, 'remove only images that don't have a custom tag set by the image

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‫field.'

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‫One thing I could do here if I wanted to make this a little more automated, is I could just take out

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‫that image command right there. Let's just remove that. Then I want to clean up real quick. I'm just

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‫going to remove my image. docker image rm custom. As you can see, it's gone there.

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‫All right. I want to do docker compose up again.

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‫And this time we'll do a -d.

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‫You'll notice throughout these examples of Compose, that it actually names containers, volumes, and

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‫networks with the name of the directory as the project name.

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‫That's actually something in Compose where, to prevent name conflicts,

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‫it will actually always add the directory name on the beginning of all of the assets so that they don't

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‫conflict with other ones.

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‫You can actually change that proxy name through the command line.

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‫If you go check out the Compose documentation.

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‫But the point I wanted to make here is if I do a docker image ls here, you'll see that it actually

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‫named my image for me.

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‫So I don't technically have to use that image option.

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‫But if I wanted a specific name for it so that I could maybe identify it later, I could.

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‫The reason I was bringing that up is this is actually a little bit cleaner because what I can do

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‫then is docker compose down, and remember in the help, it said I could use an rmi type. So when I clean

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‫it up, and I like to keep my Docker environment clean, I can do am rmi local.

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‫What that will do is actually delete those images as well.

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‫You'll see here down at the bottom that it deleted the image.

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‫Not something that I do all the time but maybe if I have a big project with lots of custom images

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‫and I don't want it to blow up my system when I'm not developing on that project, I'll use the rmi

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‫local, and it'll always keep track of the custom images it had to create.

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‫Of course, here if I use the all, it will actually delete every image that was used in this project

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‫which you may not want to do because in this case, it might delete the httpd Apache web server, and you

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‫might want that image to stay around for a while. OK.

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‫You learned a lot about Compose in this section.

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‫We're going to be using Compose throughout the rest of this course.

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‫We'll keep building on these skills as we go.