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As long as you have Node on your machine, it will output Hello world! Once we close the REPL, the process is done. This interactive terminal could be for Node, Ruby, Rails or another technology. It should say "Hey world!" So what about those images on our machine? We could run a container with this image by just running the following command: However, it looks like nothing happens. It will clean up things a lot more nicely, which you can verify by running $ docker images. We use the $ docker run command to create a container. The script runs, ends, and then the process is finished and the container closes. Nothing special, right? When Docker spins up an interactive terminal, it sometimes runs into this exact communication issue and needs the help of winpty. What we name it doesn't matter. But what is a dangling image? That's because a Docker container runs a process. That means we need to trigger a build all over again so we can copy the latest updates to script.js. Then script.js was copied again, the image was successfully built, and Docker ran our container with the image. As you'll see, a REPL for Node opens up. And also, as you can see by the size of the image, you won't want to leave it on your machine if you aren't using it. Remember that COPY command? It takes a little time but it's not the end of the world. Docker provides public images that we can pull and use. Did you get this error message after running docker run -it node? You can type exit to leave the interactive shell and close the container. cd into the docker-example directory and test it with the following command (outside of Docker): node script.js. Using our example of creating a container with an interactive Node terminal, the command should look like this: So, what's happening here? Our script still says "Hello world!" It's an image that no longer has any use and is just wasting space. $ docker-compose down has no effect on the images on our machine. Both of these configuration files can get a lot more complicated. We can add other layers on top of that but we need that base layer. And the script is absolutely essential to your work. Then run the following command: It will take a little time for your machine to download this image, but once it's done, we can take a look at a list of all our images with the following command: So this image now lives on our machine. We'll need to use a Dockerfile and docker-compose.yaml so that we can configure our Docker container to load and run our script. In this case, we only need to copy over script.js. However, having database persistence isn't expected while you are a student at Epicodus so you don't need to worry about it. Well, docker-compose is for running our container. What gives? The following command will generally clean up all dangling images. By the way, if we ever want to stop a container from running, we use the following command in the root directory of the project where we ran $ docker-compose up: Note that this will do nothing in this particular case because our process isn't continuously running. This is the working directory inside the Docker container. So let's try something out. It's a Node command. It's common to put each part of that command in an array. The solution to this issue is exactly what the message suggests: prefix the command with winpty. At the very end, our application runs Hello world! There can be multiple services specified in a docker-compose.yaml file. Okay, so how do we get this script working? Under the hood, Git Bash uses MinTTY as a terminal emulator, and MinTTY is not compatible with Windows console programs. We are inside a container now and it's walled off from the contents of our local machine. We won't need to pull it again if we need to use it. Remember, we can't run a container without an image. In the next lesson, we'll learn about using aliases, which will automate the process of prefixing your Docker commands with winpty. (If we were to remove the image from our machine, it would be downloaded again.) Last updated July 31, 2022. We are using bash instead of the Node REPL. In the process, we'll also go over some basic concepts and commands that you'll be using with Docker containers and images. Finally, we run a specified command with CMD. It is isolated from your machine's environment. It's good to run this command sometimes just to clean things up but it's not going to remove the images we've just created. The first element in the array is the command we will run (node). Then node is the image that is actually running inside the container. That's because there's no continuous process involved. We will just call it app here. We can get everything running with the following command: The output will look something like this: As you can see, all the commands in our Dockerfile are run. Nothing can get in or get out. Just to clarify, this isn't a Docker command. What if we wanted to run a Node script within Docker? This is where winpty comes in. The one situation where you'd want to be careful with docker system prune is if you want to have database persistence with your volumes. This happens to some Windows users when they try to start an interactive terminal with Docker. Try out this command: If we run this command, we'll enter an interactive bash shell. If we were to run $ docker-compose up, Docker would have to download the public image from scratch instead of using the image on our machine. But it didn't rebuild it. If we moved our Dockerfile and script.js file into another directory called some-directory, it would be build: ./some-directory instead. We'll start by adding a Dockerfile to our project with several lines: A Dockerfile always starts with FROM. This is a very simple Docker configuration and it's common to copy over entire directories, more configuration files, and so on. Lesson 4 of 10 Next, let's add a little bit to docker-compose.yaml: We are keeping this very simple. This may seem like a lot of work to run Hello world! It'll look something like this: We now have two images here: one for node and one for our newly created image. The second element in the array is what node will run (/script.js). Or rather, hello, wait a minute. Hey, wait a minute. What do you think? If we run $ docker images in the command line again, we'll even see our new image. specified here. instead of "Hello world!. First, let's actually use this one. But if you try to run $ node script.js inside this interactive shell, you'll get the following error: The reason for this error should be easy to guess. Without this command, our Docker container won't include this file. So as we can see, Docker builds our image and then runs that image inside of a container. We need to use the --build flag to do that: We triggered a build with the --build flag. We don't have to download node again because we already have the image on our machine. However, usually our containers will be running local servers and databases. Can we run this script from inside a Docker interactive terminal? Well, let's start by creating a small Node script which we'll store in a directory called docker-example: This will just print Hello world! Let's start by looking at a very simple example of Docker in action. But imagine if you'd spent the last three hours trying to install software on your machine simply because you wanted to run a script. That's potentially very inefficient and a waste of time, especially in production. To close the Node REPL, you can type .exit in the REPL. We've added just one instruction: You'll usually see a . We can even check the version of Node that's being used inside our interactive shell (node -v) and it'll quite likely be different from the version you have installed on your local machine. Well, if the script had come with a Dockerfile configuration, you wouldn't have needed to spend all that time installing that software. This is the base layer. So now we're ready for the Docker magic to happen. Note that this is the copy inside the container in our working directory not the copy of the script on our local machine. Our test example will be extremely simple so we can really focus on Docker itself. This will set the groundwork to using containers that are specific for that section's development environment. Why would it? No Dockerfile, no docker-compose.yaml in fact, no project at all. Note that our Dockerfile automatically used a cache where possible to make the process faster. Here, we specify the version of docker-compose we are using. In this lesson, we'll use Docker to build an image and run a container. Now run $ docker-compose up again. But what's actually running here is the Node REPL inside of a Docker container. It works on someone else's computer but not on yours. It just means look in the current directory for the Dockerfile, any files that need to be copied over, and so on. Next, we set a working directory with WORKDIR. to the console. Since we already have this image on our machine, it will be easy for Docker to grab it. And yeah, they are big. Note the name of the new one docker-example_app. For our purposes, it'll be common to have one service for a web application (running a local server) and another for a database. We can name our service whatever we want. Well, it may not seem like it if you already have Node installed on your machine. We won't need any configuration for this. The -it flag specifies that Docker should open an interactive Node terminal. Node is being too formal. Make sure you have Docker installed and running. It's the name of our directory with the name of the service appended to it (app). Time to experiment. The latest update isn't on our image. That means the Node REPL. Well, we are writing our script in VS Code. We can use this command instead: This command will remove all stopped containers and unused images in addition to dangling images. If you are ever in a situation where you've updated your code on your local machine and it's not updating in Docker, you probably omitted the --build flag and you need to run $ docker-compose up --build. The Dockerfile specifies the build instructions so all of those commands run again. In this case, the base layer is a Node development environment. That is on our local machine. Once again, Docker is running a container with the Node image but this time, we are using a different process. You'll notice that the node image isn't there anymore. Anytime you see the message about prefixing your Docker command with winpty, do just that. Note that this isn't the Docker version we are using, it's the version of docker-compose we are using. We'll discuss how to remove images soon. The images we have so far were very big and we don't need them anymore now that we are done with this brief Docker tutorial. These are continuously running processes and we can use $ docker-compose down to stop those containers from running. It did that very faithfully. As you'll see, it now correctly says "Hey world!". In this case, the process is the Node REPL. Install Docker, run $ docker-compose up, and you're done. Next, we indicate the services we are using. As you'll see, the container will stop running once we leave the REPL. Let's make an update to our script in VS Code. 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