#openshift
#openshift complete tutorial | Create Custom Docker Images| Docker Image from Dockerfile
Learning Objective: Design and code a Docker file to build a custom container image.
Building an Image from a Dockerfile- Using an S2I builder to create an application image simplifies the build process, as the builder does all the hard work for you. Although you can override the S2I build and deployment process for an application, the extent of the customizations you can make is restricted. You cannot, for example, install additional operating system packages or run any actions that require root privileges. In order to have full control over how the image is built and the application run, you will need to use the Docker build strategy.
The Docker Build Strategy
The Docker build strategy takes the instructions from a Dockerfile and uses them to construct a container image. The Dockerfile and associated files required to construct the image need to be in a hosted source code repository accessible to the OpenShift cluster where you perform the builds. This strategy can be used to construct an application image or an S2I builder image. The building of the image can also be linked via image triggers to any builds or deployments dependent on the image. An update to the image will therefore trigger the subsequent builds and deployments, automating your workflow.
Docker File
A text document that contains all the commands a user could call on the command line to assemble an image.
How to run commands
Add files or directories
Create environment variables
What process to run when launching container
Result from building Dockerfile is Docker image
Docker FROM instruction, Docker ADD instruction, Docker Copy, Dockerfile Commands
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