Creating a basic S2I builder image

Getting started

Files and Directories

File	Required?	Description
Dockerfile	Yes	Defines the base builder image
s2i/bin/assemble	Yes	Script that builds the application
s2i/bin/usage	No	Script that prints the usage of the builder
s2i/bin/run	Yes	Script that runs the application
s2i/bin/save-artifacts	No	Script for incremental builds that saves the built artifacts
test/run	No	Test script for the builder image
test/test-app	Yes	Test application source code

Dockerfile

Create a Dockerfile that installs all of the necessary tools and libraries that are needed to build and run our application. This file will also handle copying the s2i scripts into the created image.

S2I scripts

assemble

Create an assemble script that will build our application, e.g.:

• build python modules
• bundle install ruby gems
• setup application specific configuration

The script can also specify a way to restore any saved artifacts from the previous image.

run

Create a run script that will start the application.

save-artifacts (optional)

Create a save-artifacts script which allows a new build to reuse content from a previous version of the application image.

usage (optional)

Create a usage script that will print out instructions on how to use the image.

Make the scripts executable

Make sure that all of the scripts are executable by running chmod +x s2i/bin/*

Create the builder image

The following command will create a builder image named kunkka-centos7 based on the Dockerfile that was created previously.

docker build -t kunkka-centos7 .

The builder image can also be created by using the make command since a Makefile is included.

Once the image has finished building, the command s2i usage kunkka-centos7 will print out the help info that was defined in the usage script.

Testing the builder image

The builder image can be tested using the following commands:

docker build -t kunkka-centos7-candidate .
IMAGE_NAME=kunkka-centos7-candidate test/run

The builder image can also be tested by using the make test command since a Makefile is included.

Creating the application image

The application image combines the builder image with your applications source code, which is served using whatever application is installed via the Dockerfile, compiled using the assemble script, and run using the run script. The following command will create the application image:

s2i build test/test-app kunkka-centos7 kunkka-centos7-app
---> Building and installing application from source...

Using the logic defined in the assemble script, s2i will now create an application image using the builder image as a base and including the source code from the test/test-app directory.

Running the application image

Running the application image is as simple as invoking the docker run command:

docker run -d -p 5678:5678 kunkka-centos7-app

The application, which consists of a simple static web page, should now be accessible at http://localhost:5678.

Using the saved artifacts script

Rebuilding the application using the saved artifacts can be accomplished using the following command:

s2i build --incremental=true test/test-app nginx-centos7 nginx-app
---> Restoring build artifacts...
---> Building and installing application from source...

This will run the save-artifacts script which includes the custom code to backup the currently running application source, rebuild the application image, and then re-deploy the previously saved source using the assemble script.