http://127.0.0.1:8080 in the browser, you'll see a default response page.custom-nginx in there. Now, create a new file named Dockerfile inside that directory. A Dockerfile is a collection of instructions that once processed by the daemon, results into an image. Content for the Dockerfile is as follows:Dockerfile starts with a FROM instruction. This instruction sets the base image for your resultant image. By setting ubuntu:latest as the base image here, you get all the goodness of Ubuntu already available in your custom image hence, you can use things like the apt-get command for easy package installation.EXPOSE instruction is used to indicate the port that needs to be published. Using this instruction doesn't mean that you won't need to --publish the port. You'll still need to use the --publish option explicitly. This EXPOSE instruction works like a documentation for someone who's trying to run a container using your image. It also has some other usages that I won't be discussing here.RUN instruction in a Dockerfile executes a command inside the container shell. The apt-get update && apt-get install nginx -y command checks for updated package versions and installs NGINX. The apt-get clean && rm -rf /var/lib/apt/lists/* command is used for clearing the package cache because you don't want any unnecessary baggage in your image. These two commands are simple Ubuntu stuff, nothing fancy. The RUN instructions here, are written in shell form. These can also be written in exec form. You can consult the official reference for more information.CMD instruction sets the default command for your image. This instruction is written in exec form here comprising of three separate parts. Here, nginx refers to the NGINX executable. The -g and daemon off are options for NGINX. Running NGINX as a single process inside containers is considered a best practice hence the usage of this option. The CMD instruction can also be written in shell form. You can consult the official reference for more information.Dockerfile you can build an image out of it. Just like the container related commands, the image related commands can be issued using the following syntax:Dockerfile you just wrote, open up your terminal inside the custom-nginx directory and execute the following command:Dockerfile and the build context. In the issued command above:docker image build is the command for building the image. The daemon finds any file named Dockerfile within the context.. at the end sets the context for this build. The context means the directory accessible by the daemon during the build process.container run command coupled with the image ID that you received as the result of the build process. In my case the id is 3199372aa3fc evident by the Successfully built 3199372aa3fc line in the previous code block.http://127.0.0.1:8080 and you should see the default response page.--tag or -t option is used in such cases. Generic syntax for the option is as follows:docker container run mysql:5.7 where mysql is the image repository and 5.7 is the tag.custom-nginx:packaged you can execute the following command:custom-nginx:packaged instead of some long random string.image tag command to do that:container ls command, you can use the image ls command to list all the images in your local system:image rm command. The generic syntax is as follows:custom-nginx:packaged image, you may execute the following command:image prune command to cleanup all un-tagged dangling images as follows:--force or -f option skips any confirmation questions. You can also use the --all or -a option to remove all cached images in your local registry.custom-nginx:packaged image from the previous sub-section.image history command. The various layers of the custom-nginx:packaged image can be visualized as follows:d70eaf7277ea to 7f16387f7307 image. I'll ignore the bottom four layers where the IMAGE is <missing> as they are not of our concern.Dockerfile will create a layer in the image.d70eaf7277ea was created by /bin/sh -c #(nop) CMD ["/bin/bash"] which indicates that the default shell inside Ubuntu has been loaded successfully.6fe4e51e35c1 was created by /bin/sh -c #(nop) EXPOSE 80 which was the second instruction in your code.587c805fe8df was created by /bin/sh -c apt-get update && apt-get install nginx -y && apt-get clean && rm -rf /var/lib/apt/lists/* which was the third instruction in your code. You can also see that this image has a size of 60MB given all necessary packages were installed during the execution of this instruction.7f16387f7307 was created by /bin/sh -c #(nop) CMD ["nginx", "-g", "daemon off;"] which sets the default command for this image.FROM, EXPOSE, RUN and CMD instructions. In this sub-section you'll be learning a lot more about other instructions.apt-get in the previous example.nginx-1.19.2.tar.gz inside the custom-nginx directory. You'll use this archive as the source for building NGINX.nginx-1.19.2.tar.gz file inside the image.make tool.nginx executable.Dockerfile and update its contet as follows:Dockerfile reflects the seven steps I talked about beforehand.FROM instruction sets Ubuntu as the base image making an ideal environment for building any application.RUN instruction installs standard packages necessary for building NGINX from source.COPY instruction here is something new. This instruction is responsible for copying the the nginx-1.19.2.tar.gz file inside the image. The generic syntax for the COPY instruction is COPY <source> <destination> where source is in your local filesystem and the destination is inside your image. The . as the destination means the working directory inside the image which is by default / unless set otherwise.RUN instruction here extracts the contents from the archive using tar and gets rid of it afterwards.nginx-1.19.2 containing the source code. Hence on the next step, you'll have to cd inside that directory and perform the build process. You can read the How to Install Software from Source Code… and Remove it Afterwards article at It's Foss to learn more on the topic.nginx-1.19.2 directory using rm command.nginx-1.19.2.tar.gz, you can create an argument using the ARG instruction. This way, you'll be able to change the version or filename by just changing the argument.COPY called the ADD instruction which is capable of adding files from the internet.Dockerfile file and update it's content as follows:ARG on line 13, 14 and the usage of the ADD instruction on line 16. Explanation for the updated code is as follows:ARG instruction lets you declare variables like in other languages. These variables or arguments can later be accessed using the ${argument name} syntax. Here, I've put the filename nginx-1.19.2 and the file extension tar.gz in two separate arguments. This way I can switch between newer versions of NGINX or the archive format by making a change in just one place. In the code above, I've added default values to the variables. Variable values can be passed as options of the image build command as well. You can consult the official reference for more details.ADD instruction, I've formed the download URL dynamically using the arguments declared above. The https://nginx.org/download/${FILENAME}.${EXTENSION} line will result in something like https://nginx.org/download/nginx-1.19.2.tar.gz during the build process. You can change the file version or the extension by changing it in just one place thanks to the ARG instruction.ADD instruction doesn't extract files obtained from the internet by default hence, the usage of tar on line 18.custom-nginx:built-v2 image.custom-nginx:built-v2 image has been successfully run. The container should be accessible at http://127.0.0.1:8080 address now.image ls command:Dockerfile first:RUN instruction installs a lot of stuff. Although these packages are necessary for building NGINX from source, they are not necessary for running it. Out of the 6 packages that we installed, only two are necessary for running NGINX. These are libpcre3 and zlib1g. So a better idea can be to uninstall the other packages once the build process is done.Dockerfile as follows:RUN instruction is doing all the necessary heavy-lifting. The exact chain of events is as follows:libpcre3 and zlib1g packages are needed for running NGINX hence they're kept.RUN instruction instead of nicely splitting them into multiple instructions, like we did previously. Well that's a mistake. If you install packages and then remove them in separate RUN instructions, they'll live in separate layers of the image. Although the final image will not have the removed packages, their size will still be added to the final image given they exist in one of the layers consisting the image. So make sure you make these kind of changes on a single layer.Dockerfile and see the differences.musl libc and busybox and is lightweight. Where the latest ubuntu image weighs at around 28MB, alpine is 2.8MB. Apart from the lightweight nature, Alpine is also secure and is a much better fit for creating containers than the other distributions.custom-nginx image by using the alpine image as its base.Dockerfile and update its content as follows:apt-get install for installing packages, we use apk add and the --no-cache option means that the downloaded package won't be cached. Likewise apk del is used instead of apt-get remove to uninstall packages.--virtual option for apk add command is used for bundling a bunch of packages into a single virtual package for easier management. Packages that are needed only for building the program is labeled as .build-deps which is then removed on line 29 by executing apk del .build-deps command. You can learn more about virtuals in the official docs.Dockerfile and see the difference in file size:apk package manager, there are some other things that differ in Alpine from Ubuntu but they're not that much of big deal. You can just search the internet whenever you get stuck.rmbyext application resides inside the sub-directory with the same name.Dockerfile take a moment to plan out what the final output should be. In my opinion it should be like something as follows:rmbyext script.rmbyext script should be set as the entrypoint so the image can take extension names as arguments.rmbyext as the entry-point for this image.Dockerfile inside the rmbyext directory and put following code in it:FROM instruction sets python as the base image making an ideal environment for running python scripts. The 3-alpine tag indicates that you want the Alpine variant of Python 3.WORKDIR instruction sets the default working directory to /zone here. The name of the working directory is completely random here. I found zone to be a fitting name, you may use anything you want.rmbyext script is installed from GitHub, git is an install time dependency. The RUN instruction on line 5 installs git then installs the rmbyext script using git and pip. It also gets rid of git afterwards.ENTRYPOINT instruction sets the rmbyext script as the entry-point for this image.latest by default. You should be able to run the image as you saw in the previous section. Remember to refer to the actual image name you've set, instead of fhsinchy/rmbyext here.--tag or -t option is as follows:custom-nginx image online. To do so, open up a new terminal window inside the custom-nginx project directory. To share an image online, you'll have to tag it following the <docker hub username>/<image name>:<image tag> syntax. My username is fhsinchy so the command will look like as follows:fhsinchy/custom-nginx is the image repository and latest is the tag. The image name can be anything you want and can not be changed once you've uploaded the image. The tag can be changed whenever you want and usually reflects the version of the software or different kind of builds.node image as an example. The node:lts image refers to the long term support version of Node.js whereas the node:lts-alpine version refers to the Node.js version built for Alpine Linux which is much smaller than the regular one.latest. But that doesn't mean that the latest tag will always refer to the latest version. If for some reason you explicitly tag an older version of the image as latest then Docker will not make any extra effort to cross check that.