Pipeline CRD

This repo contains the API definition of the Pipeline CRD and an on cluster implementation of that API. The goal of the Pipeline CRD is to provide k8s-style resources that allow the declaration of CI/CD-style pipelines, which can be backed by any arbitrary implementation.

Features the Pipeline CRD will support include:

• Conditional, parallel and distributed execution
• Interaction with CI/CD resources such as source code, artifacts, resutls, deployments and clusters

The goal of the Pipeline CRD is to fit into and cooperate with the Knative ecosystem, specifically:

• The Build CRD
• The Eventing APIs

See examples for some examples of how this is intended to work.

The CRDs involved are:

• Task
• Pipeline
• PipelineParams
• TaskRun
• PipelineRun
• Resources

High level details of this design:

• Pipelines do not know what will trigger them, they can be triggered by events or by manually creating PipelineRuns
• Tasks can exist and be invoked completely independently of pipelines; they are highly cohesive and loosely coupled
• Test results are a first class concept, being able to navigate test results easily is powerful (e.g. see failures easily, dig into logs, e.g. like the Jenkins test analyzer plugin)
• Tasks can depend on artifacts, output and parameters created by other tasks.
• Resources are the artifacts used as inputs and outputs of TaskRuns.

Task

Task is a CRD that knows how to instantiate a Knative Build, either from a series of steps (i.e. Builders) or from a BuildTemplate. It takes Knative Build and adds inputs and outputs. Where these inputs and outputs are provided from is not known to a task, so they can be provided by a Pipeline or by a user invoking a Task directly.

Tasks are basically Knative BuildTemplates with additional input types and clearly defined outputs.

Pipeline

Pipeline describes a graph of Tasks to execute. It defines the DAG and expresses how all inputs (including PipelineParams and outputs from previous Tasks) feed into each Task.

Dependencies between parameters or inputs/outputs are expressed as references to k8s objects.

PipelineParams

PipelineParams contains parameters for a Pipeline. One Pipeline can be invoked with many different instances of PipelineParams, which can allow for scenarios such as running against PRs and against a user’s personal setup. PipelineParams can control:

• Which serviceAccount to use (provided to all tasks)
• Where results are stored (e.g. in GCS)

TaskRun

Creating a TaskRun will invoke a Task, running all of the steps until completion or failure. Creating a TaskRun will require satisfying all of the input requirements of the Task.

TaskRuns are basically Knative Builds with inputs and outputs, and in the future we may want to transition Builds to become Tasks.

TaskRuns can be created directly by a user or by a PipelineRun.

TaskRun Status

Once a TaskRun has been created, it will start excuting its steps sequentially. The conditions field will be updated as the TaskRun executes:

• The Started condition will be added when the first step starts.
• The Completed condition will be added when the last step completes, or after a non-zero exit code from a step.
• The Successful condition will be added after the Completed condition and will indicate if the run succeeded or failed.

When the TaskRun has completed, the steps field will indicate the exit code of all steps that completed.

PipelineRun

Creating a PipelineRun executes the pipeline, creating TaskRuns for each task in the pipeline.

PipelineRuns tie together a Pipeline and a PipelineParam. A PipelineRun could be created:

• By a user manually
• In response to an event (e.g. in response to a Github event, possibly processed via Knative eventing)

PipelineRun Status

Once a PipelineRun has been created, it will start excuting the DAG of its Tasks by creating a TaskRun for each of them. The conditions field will be updated as the PipelineRun executes:

• The Started condition will be added when the first TaskRun is created.
• The Completed condition will be added when the last TaskRun completes (or fails).
• The Successful condition will be added after the Completed condition and will indicate if the PipelineRun succeeded or failed.

When the PipelineRun has completed, the taskRuns field will contain references to all TaskRuns which were executed and their next and previous TaskRuns.

Resources

Resources in a pipelines are the set of objects that are going to be used as inputs and outputs of a TaskRun.

• Resources is created directly in a pipeline configuration and bound to TaskRun as an input and/or output source.
• The (optional) passedConstraint key on an input source defines a set of previous task names.
• When the passedConstraint key is specified on an input source, only the version of the resource that passed through the defined list of tasks is used.
• The passedConstraint allows for Tasks to fan in and fan out, and ordering can be expressed explicitly using this key since a task needing a resource from a another task would have to run after.