This portion of the course will explain the anatomy of a Dockerfile, and how that file is used to generate containers.
To begin, create a new file named Dockerfile in an empty directory. Paste the contents below into Dockerfile.
FROM nginx:latest
Within the directory where you created Dockerfile, run the following command:
docker build -t mycontainer:001 .Assuming all goes well, you should see the following similar output:
$ docker build -t mycontainer:001 .
Sending build context to Docker daemon 2.048kB
Step 1/1 : FROM nginx:latest
latest: Pulling from library/nginx
461246efe0a7: Pull complete
a96aaf9a9ec3: Pull complete
650d8b758441: Pull complete
b138da793ac8: Pull complete
bb1705539683: Pull complete
b9ed43dcc388: Pull complete
Digest: sha256:db345982a2f2a4257c6f699a499feb1d79451a1305e8022f16456ddc3ad6b94c
Status: Downloaded newer image for nginx:latest
---> 41b0e86104ba
Successfully built 41b0e86104ba
Successfully tagged mycontainer:001
We have effectively created a clone of the official nginx:latest container. A Dockerfile is a series of steps describing how to build a container, or how to extend an existing container with your customizations.
Let's break down the effects of our docker build command, and the FROM nginx:latest contents of our Dockerfile.
This command tells Docker you want to build a new container, name it mycontainer, with a tag of 001, and it should expect to find Dockerfile in the current directory. The last argument to the docker build command is a . character. That argument tells Docker where to look for Dockerfile. The . character is a UNIX concept that translates to the current directory you are in.
The first line in a Dockerfile specifies which existing container we intend to modify. Subsequent lines detail those modifications...but we don't specify any of those. Therefore we end up with a perfect clone of the nginx:latest container. By default, if a container does not exist on your local computer, Docker will attempt to look it up on Docker Hub. You can view the nginx container we are using on Docker Hub with this link.
Start your container with the following command:
docker run -p 38080:80 mycontainer:001That command does more than start the container, it also tells Docker to forward traffic to your localhost on port 38080 inside the container to port 80. This particular container happens to be a web server that listens on port 80. Forwarding port 38080 means that we can use our local computers web browser and visit http://localhost:38080, which would send our web request to the container.
If you have curl available, try it out to see the response from nginx:
curl 'http://localhost:38080/'You should see output resembling:
$ curl 'http://localhost:38080/'
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
Let's modify our nginx container to send back different output. If you're familiar with nginx, you probably know that by default, it serves web traffic from /usr/share/nginx/html. We can add content to that directory and our container will serve it back to us. Let's extend our Dockerfile with the example below:
FROM nginx:latest
RUN echo "Hello World!" > /usr/share/nginx/html/index.html
Build the container again with the command we used earlier...but this time let's increment the tag to from 001 to 002.
docker build -t mycontainer:002 .Now run the new container we just built, which is tagged mycontainer:002.
docker run -p 38080:80 mycontainer:002Now curl the container and see the response has changed to reflect us writing index.html to the correct path within the container.
$ curl 'http://localhost:38080/'
Hello World!
In the previous example, we edited index.html by using the echo command during the build process. This works, but there is a more efficient and elegant way to add files to a container. Next, we'll add a more polished website template named Dashmin.
For this example, you'll need to clone this git repository, and navigate to containercourse/resources/part001/dashmin.
Open the Dockerfile in that directory.
FROM nginx:latest
ADD dashmin_files/ /usr/share/nginx/html/
Notice how the echo command has been swapped for ADD. This command recursively copies all the files within the dashmin_files directory to /usr/share/nginx/html/ within the container.
Let's build the new container and see the output. Use the command below to build - notice how we've incremented our tag from 002 to 003.
docker build -t mycontainer:003 .Now run the container with the same command we've used previously, referencing the new tag.
docker run -p 38080:80 mycontainer:003Once the container is running, visit http://localhost:38080 to see the website.
The Dashmin website is a free and open source template. For more information about it visit it's official website at https://htmlcodex.com/bootstrap-admin-template-free.
A complete listing of all syntax and documentation for the Dockerfile format is available on the official Docker website, at https://docs.docker.com/engine/reference/builder/.