Time to take on your first Docker Compose file! You'll be creating a Compose
file for the nginx Dockerfile you made in Phase 1 of the Dockerfiles Galore
project.
Start off by taking a look at the skeleton. You've already created
the Dockerfile, so all you'll need to do is create a docker-compose.yml file
to build your custom image and start a container with a single command. If you
are unsure about syntax or would like to see an example, the Docker
Compose documentation is wonderfully thorough.
Reminder: indentation is how the YAML file formats group information, so indentation is important. Check out this quick YAML reference.
You'll start off, as with every Docker Compose file, by specifying the version
of Docker Compose you'll be using. For this docker-compose.yml use version
"3". Next, you'll be defining your services (the containers you'll be running).
Create a service named nginx. Your file should look like this:
version: "3"
services:
nginx:
Now you'll need to tell Compose to build a custom image for you. Reference the
build documentation if you need any guidance about syntax. Make
sure to name the image by adding a image command below your build command.
Finally, you'll want to tell Docker Compose which ports you want to expose when
it creates the container for you. Expose your local port 80, aiming traffic at
port 80 in the container.
Linux Users: Some students using Linux have had trouble exposing port 80 locally. If this happens, feel free to use port 81 instead.
Awesome! Use docker-compose up and when Compose tells you the container is
attached to the network, it will then "hang". Now try going to
http://localhost:80.
Awesome! Make sure to check out the color coded logs that Compose provides you
for each container. Now stop the server and use docker-compose down to have
compose automatically stop and remove the container it started up.
However, what if you wanted to change the HTML? Head into the index.html we
provided and change the text inside of the h1 tag. What happens if you use
docker-compose up again? Wait a second... the text doesn't change!
What you've just encountered is a common error with Compose. This error is so common you are even warned about it in the logs:
WARNING: Image for service custom-nginx was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
If you change your Dockerfile, or any source code your Dockerfile is using
in order to build your image, you will need to command Compose to rebuild the
image for you. Otherwise, Compose will use the previous image it built. You can
tell Docker Compose to rebuild your image by using the docker-compose up --build or docker-compose build command. Now let's try using Compose in
detached mode: docker-compose up -d --build to re-start your nginx server and
head to localhost:80 to see your HTML change.
Good job! Feel free to commit this file to Github for later use. Make sure to
use docker-compose down to clean up your container, or you could add the
--rmi to tell Compose to additionally remove the image it built.
In this project, you've used Docker Compose commands to build an image and run a single container - note that this is not the most common use case for Docker Compose. Where Compose really shines is running multiple containers, and effectively your whole application, with a single command. You'll get into more complex Compose files in the next project, but for now, be proud of your first Docker Compose file!