Assembling a pipeline

A Pipeline represents a CI/CD flow and is defined by the Tasks to be executed. It specifies how the Tasks interact with each other and their order of execution using the inputs , outputs, and the run-After parameters. It is designed to be generic and reusable in multiple applications and environments.

For this tutorial, we create a Pipeline that takes the source code of the Spring PetClinic application from GitHub, builds the application, and deploys it on OpenShift as outlined below:

Procedure

Copy the contents of the following sample Pipeline YAML file and save it:
```
apiVersion: tekton.dev/v1alpha1
kind: Pipeline
metadata:
  name: petclinic-deploy-pipeline
spec:
  resources:
  - name: app-git
    type: git
  - name: app-image
    type: image
  tasks:
  - name: build
    taskRef:
      name: s2i-java-8
    params:
      - name: TLSVERIFY
        value: "false"
    resources:
      inputs:
      - name: source
        resource: app-git
      outputs:
      - name: image
        resource: app-image
  - name: deploy
    taskRef:
      name: openshift-client
    runAfter:
      - build
    params:
    - name: ARGS
      value: "rollout latest spring-petclinic"
```
This Pipeline performs the following tasks:
- Clones the source code of the application from a Git repository (app-git resource).
- Builds the container image using the S2I task which generates a Dockerfile for the application and uses Buildah to build an image.
- The application image is then pushed to an image registry (app-image resource).
- The new application image is deployed on OpenShift using the OpenShift-CLI.
  
  Note that, the Pipeline YAML file contains no references to the PetClinic Git repository and its image in the registry. These are defined in the PipelineResources.
  
  Pipeline s in Tekton are designed to be generic and re-usable across environments and stages through the applications lifecycle. They abstract away the specifics of the Git source repository and image registries to be used during Pipeline execution.
  
  The execution order of the tasks is determined by the dependencies defined between the tasks using the inputs and outputs parameters, and the explicit orders that are defined using runAfter.

Create the Pipeline:

$ oc create -f https://raw.githubusercontent.com/openshift/pipelines-tutorial/master/resources/petclinic-deploy-pipeline.yaml

Verify that the Pipeline has been added to the application as follows:

$ tkn pipeline ls

NAME             AGE             LAST RUN   STARTED   DURATION   STATUS
deploy-pipeline   8 seconds ago   ---        ---       ---        ---