As neat as it is to quickly run preexisting images, we probably want to explore how we can create our own images. In this section, we'll be taking a look at Dockerfile.
A Dockerfile is the traditional naming of a file which contains instructions on how to build an image.
Before we start making Docker images, it's best if we familiarize ourselves with how images are stored in your Docker host (effectively, your laptop). Run the following command to get a list:
podman images
This will produce a list of images on your laptop that look like this:
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-world latest fce289e99eb9 3 weeks ago 1.84kB
busybox latest 3a093384ac30 3 weeks ago 1.2MB
nginx latest 7042885a156a 4 weeks ago 109MB
This effectively lists the images you have, the tags they are associated with, and the image ID. Note that you can also use image IDs as a reference when running Docker commands. Like so:
podman run -it 7042885a156a /bin/bash
Okay! Now let's make us some images. In the docker-101 directory, you'll find a file called Dockerfile. Inside this file, you'll see:
FROM nginx:mainline-alpine
This basically means that we're starting from the nginx:mainline-alpine image at the starting layer. This layer contains similar things to the nginx container you were running earlier.
To build the image, we can then run the following from inside the docker-101 directory:
podman build -t banana-smith-image .
This takes our Dockerfile file, reads the instructions, and creates the basic image on your Docker host called banana-smith-image. Again, change the name if you want. You can verify that the image is built by listing the images you now have:
podman images
You should see the image you just created. Finally, run the image by running:
podman run -d -P --name banana-smith-container banana-smith-image
To see that it's actually running, check the port by:
podman port banana-smith-container
If you get an error, something like :
podman: Error response from daemon: Conflict. The container name "/banana-smith-container" is already in use by container "dd22b733a855cafc3a9235efbe892828ca82a9ee02cd30b9c7120ba891825414". You have to remove (or rename) that container to be able to reuse that name.
See 'docker run --help'.
this might be because you already had a banana-smith-container and a banana-smith-image. You can remove the container by running
podman rm banana-smith-container
Error response from daemon: You cannot remove a running container b854db1f962007c030a3609683903644511337cde67da69d45d5702240a8cb9a. Stop the container before attempting removal or force remove
We need to stop the container first by running
podman stop banana-smith-container
Let's try that again:
podman rm banana-smith-container
and remove the image by running
podman image rm banana-smith-image
Then try building the image again.
Then open up your browser, and access the same page - e.g., http://localhost:32768. Once done, cleanup the running container by running:
podman stop banana-smith-container
Now, in the docker-101 directory, you'll find a file called index.html. Unfortunately, I have no eye for design - so feel free to modify the page to make it look as good as possible.
For the next section, we're going to be modifying our Dockerfile so that 1.) We replace the configuration, and 2.) We insert our index.html file. We'll do this by changing the Dockerfile so it looks like this:
FROM nginx:mainline-alpine
RUN rm /etc/nginx/conf.d/*
ADD wassup.conf /etc/nginx/conf.d/
ADD index.html /usr/share/nginx/html/
The RUN directive runs the command specified (in this case, rm /etc/nginx/conf.d/* - which cleans out the configuration directory for Nginx). The ADD directive adds the files from your current directory into the image's directories. What we're doing here is we're basically:
1.) Referencing the nginx:mainline-alpine image to start with
2.) Removing existing configuration files
3.) Adding a new configuration file (wassup.conf)
4.) And adding a new index.html file.
To build the image, run the same command as before:
podman build -t banana-smith-image .
Now, if you list out your images with docker images, you'll see something like:
REPOSITORY TAG IMAGE ID
banana-smith-image latest 98be87baf87e
hello-world latest fce289e99eb9
busybox latest 3a093384ac30
nginx latest 7042885a156a
What you might have noticed is that the IMAGE ID is now different. Run it the way you've run any other image:
podman run -d -P --name banana-smith-container banana-smith-image
Then check the port it's running under:
podman port banana-smith-container
Then open up your browser, and access the same page - e.g., http://localhost:32768. What you should see is your new, fresh image!
Why not try adding CSS to the index.html page?