The simplest Docker image you can ever imagin!

This is the 4-line code for the simplest Docker image. BUT

1. What is this FROM scratch ?
2. Do we need a base image like ubuntu or alpine ?
3. What are the benefits of doing this ?

let's answer these all questions !

Lets clear the basics first

Running a Docker container means running the single application inside the Docker container. The single application is nothing but a process inside the host machine.

We use different base images, like ubuntu and alpine Because these images contain the files and dependencies which our application may require to run.

Ever wondered how the base images are made?

Every Docker image starts with an empty image called scratch which is empty inside, meaning it has nothing inside it. The files and folders required are copied inside it.
Let's take an example of the base image 'ubuntu`.

linux directory example

all the directory structure are created and all the required files are copied inside the scratch image and finally base image ubuntu is created.

so, ubuntu base image is nothing but a file & directory structures copied inside a scratch image.

If your application requires nothing else than your application binary, then you can just copy the binary inside the scratch base image and it will work. and this is what we are doing in the 4-line docker image file.

Answering the question.

1. What is this FROM scratch ?

Ans: scratch is a keyword in docker which tells docker that you are starting an empty image and you will copy files as required and nothing else than that.

1. Do we need a base image like ubuntu or alpine ?

Ans: if your application doesnot depends on any files or programs inside these image than you donot require them, you can just start from scratch.

1. What are the benefits of doing this ?

Ans: It minimizes the image size as much as possible. Additionally, since your Docker image includes only the necessary components, it reduces the risk of security vulnerabilities.

Things to remember

When you write your application in compiled languages like C Rust, Golang you must compile it into a static binary. Static binary refers to a binary of your application that does not require anything from the operating system and contains all the dependencies required by it. This allows the application to run independently. Read more here

Conclusion

You can use scratch to create image of your application which will be super simplified, containing only the required components and nothing else which makes your image smaller and less prone to security issues.

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Comments

[Sagar Chaurasia]

Great, sir I need this type of blog your knowledge is amazing

[Thinley]

Cleared my doubt on base image and will try to use scratch to create image for my application.
Need hands on using scratch to create image for application.

[Tanmay]

fantastic