Reduce Docker Image size by Using Multi stage build

In Docker, one of the main issues is the size of the final image. It’s not uncommon to end up with images over 1 GB even for simple Java applications.

Since version 17.05 of Docker, it’s possible to have multiple builds in a single Dockerfile, and to access the output of the previous build into the current one.

Those are called multi-stage builds. The final image will be based on the last build stage.

Now, we will create two docker images: one without multi-stage builds and another with multi-stage builds and compare the size of both.

Let’s consider one maven project, which is hosted on GitHub and we have to build that project and deploy it on Tomcat server.

1.So, First we will install JAVA as below

2. then Install Git and clone repository

3. Now, install maven and build maven project to create WAR file i.e webapp.war

4. Finally, we have to install tomcat and after configuration, copy WAR file into webapps folder and start service.

Complete dockerfile will look like this:

To create multi stage build image, follow these steps:

1. First, create a directory by name “with_MSB” and a dockerfile in it and add the above content.

2. Build image by using below command

3. To create Container, run below command

4. Now, you can check your application on browser

5. Check image size by using below command

Image size will be more than 600MB

6. Stop container and remove it by using below command

Now create docker image with multi-stage builds for same application

So build stages would be as follows:

1. Clone the Maven project repository from Git.

2. Copy the files from the previous stage and build the app with Maven.

3. Copy the WAR file from the previous stage deploys it on Tomcat i.e in webapp folder.

Complete dockerfile will look like this

# Dockerfile

To create multi-stage builds image,

1. First, create directory “with_MSB” and dockerfile in it and add the above content.

2. Build image by using below command

3. To create Container run below command

4. Now you can check your application on browser

5. Check image size by using below command

Image size will be 6 times less than earlier size (without multi-stage build image)

6. Stop container and remove it by using below command

Conclusion:

We have created two images here, one without multi-stage i.e app_image and another one by using multi-stage i.e app_image_msb.

We have noticed that app_image_msb size is 6 times lesser than app_image.

So by using multi-stage build we can reduce the size of the image.