OpenShift - Build Automation

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In OpenShift, we have multiple methods of automating the build pipeline. In order to do that we need to create a BuildConfig resource to describe the build flow. The flow in BuildConfig can be compared with the job definition in Jenkins job definition. While creating the build flow, we have to choose the build strategy.

BuildConfig File

In OpenShift, BuildConfig is a rest object used to connect to API and then create a new instance.

kind: "BuildConfig"
apiVersion: "v1"
metadata:
   name: "<Name of build config file>"
spec:
   runPolicy: "Serial"
   triggers:
   -
      type: "GitHub"
      github:
         secret: "<Secrete file name>"
   - type: "Generic"
   generic:
      secret: "secret101"
   -
   type: "ImageChange"
   source:
      type: "<Source of code>"
      git:
   uri: "https://github.com/openshift/openshift-hello-world"
   dockerfile: "FROM openshift/openshift-22-centos7\nUSER example"
   strategy:
      type: "Source"
      
sourceStrategy:
   from:
      kind: "ImageStreamTag"
      name: "openshift-20-centos7:latest"
   output:
      to:
         kind: "ImageStreamTag"
         name: "origin-openshift-sample:latest"
   postCommit:
      script: "bundle exec rake test"

In OpenShift, there are four types of build strategies.

• Source-to-image strategy
• Docker strategy
• Custom strategy
• Pipeline strategy

Source-to-image Strategy

Allows creating container images starting from the source code. In this flow, the actual code gets downloaded first in the container and then gets compiled inside it. The compiled code gets deployed inside the same container and the image is built from that code.

strategy:
   type: "Source"
   sourceStrategy:
      from:
         kind: "ImageStreamTag"
         name: "builder-image:latest"
      forcePull: true

There are multiple strategy policies.

• Forcepull
• Incremental Builds
• External Builds

Docker Strategy

In this flow, OpenShift uses Dockerfile to build the image and then upload the created images to the Docker registry.

strategy:
   type: Docker
   dockerStrategy:
      from:
         kind: "ImageStreamTag"
         name: "ubuntu:latest"

Docker file option can be used in multiple locations starting from file path, no cache, and force pull.

• From Image
• Dockerfile path
• No cache
• Force pull

Custom Strategy

This is one of the different kinds of build strategy, wherein there is no such compulsion that the output of the build is going to be an image. It can be compared to a free style job of Jenkins. With this, we can create Jar, rpm, and other packages.

strategy:
   type: "Custom"
   customStrategy:
      from:
         kind: "DockerImage"
         name: "openshift/sti-image-builder"

It consists of multiple build strategies.

• Expose Docker socket
• Secrets
• Force pull

Pipeline Strategy

Pipeline strategy is used to create custom build pipelines. This is basically used to implement the workflow in the pipeline. This build flow uses custom build pipeline flow using Groovy DSL language. OpenShift will create a pipeline job in Jenkins and execute it. This pipeline flow can also be used in Jenkins. In this strategy, we use Jenkinsfile and append that in the buildconfig definition.

Strategy:
   type: "JenkinsPipeline"
   jenkinsPipelineStrategy:
   jenkinsfile: "node('agent') {\nstage 'build'\nopenshiftBuild(buildConfig: 'OpenShift-build', showBuildLogs: 'true')\nstage 'deploy'\nopenshiftDeploy(deploymentConfig: 'backend')\n}"

Using build pipeline

kind: "BuildConfig"
apiVersion: "v1"
metadata:
   name: "test-pipeline"
spec:
   source:
      type: "Git"
      git:
         uri: "https://github.com/openshift/openshift-hello-world"
   strategy:
      type: "JenkinsPipeline"
      jenkinsPipelineStrategy:
         jenkinsfilePath: <file path repository>