Alauda DevOps Pipelines Docs

TaskRuns

A TaskRun is a Kubernetes Custom Resource that instantiates a Task for execution. TaskRuns are responsible for executing the steps defined in a Task and managing their lifecycle, providing a way to run Tasks either standalone or as part of a Pipeline.

TOC

Why TaskRuns are Needed

CI/CD Execution Challenges

In CI/CD systems, there are several challenges related to task execution:

  • Execution Tracking: Need to track the progress and status of each task execution
  • Resource Allocation: Need to allocate appropriate resources for each task
  • Input/Output Management: Need to manage inputs to and outputs from task executions
  • Error Handling: Need to handle failures and provide debugging information
  • Auditability: Need to maintain a record of all task executions for auditing purposes

Tekton's Solution

Tekton TaskRuns address these challenges by:

  • Execution Instance: Each TaskRun represents a single execution of a Task with specific inputs
  • Status Tracking: TaskRuns track the status of each Step's execution
  • Resource Binding: TaskRuns bind actual resources (volumes, credentials) to Task requirements
  • Result Collection: TaskRuns collect and store the results produced by Tasks
  • Kubernetes Integration: TaskRuns leverage Kubernetes for resource management and scheduling

Advantages

  • Isolation: Each TaskRun executes independently, allowing parallel execution of the same Task
  • Traceability: TaskRuns provide detailed execution history and logs
  • Flexibility: TaskRuns can override Task parameters and workspace bindings
  • Reusability: The same Task can be executed with different inputs via different TaskRuns
  • Integration: TaskRuns can be triggered by various systems through Kubernetes API
  • Observability: TaskRun status and logs can be monitored through Kubernetes tools

Scenarios

TaskRuns are useful in various scenarios, including:

  • Manual Task Execution: Running a Task on-demand for testing or debugging
  • Scheduled Operations: Running Tasks on a schedule for maintenance operations
  • Event-Driven Execution: Triggering Tasks in response to external events
  • Pipeline Components: Executing Tasks as part of a larger Pipeline
  • CI/CD Operations: Building, testing, and deploying applications

Constraints and Limitations

  • TaskRuns execute on a single Kubernetes node and cannot span multiple nodes
  • Once started, TaskRun parameters cannot be modified
  • TaskRuns have limited retry capabilities for failed Steps
  • TaskRun execution time is limited by the Kubernetes pod timeout
  • TaskRuns cannot be paused once they start executing

Principles

TaskRun Execution Model

When a TaskRun is created:

  1. Tekton validates the TaskRun specification
  2. Kubernetes creates a Pod for the TaskRun
  3. Each Step in the Task becomes a container in the Pod
  4. Tekton injects an entrypoint binary into each Step container
  5. Steps run sequentially in the order defined in the Task
  6. The TaskRun status is updated as each Step completes
  7. Results are collected and stored in the TaskRun status
  8. The Pod is terminated when all Steps complete or on failure

TaskRun Status

The TaskRun status provides detailed information about the execution:

  1. Overall status (Running, Succeeded, Failed, etc.)
  2. Start and completion times
  3. Individual Step statuses
  4. Task results
  5. Reason for failure (if applicable)
  6. Pod name for accessing logs

Configuration Examples

Basic TaskRun Example

apiVersion: tekton.dev/v1
kind: TaskRun
metadata:
  name: build-app-run
spec:
  taskRef:
    name: build-app
  params:
    - name: image
      value: my-registry/my-app:latest
  workspaces:
    - name: source
      persistentVolumeClaim:
        claimName: app-source-pvc

TaskRun with Embedded Task Definition

apiVersion: tekton.dev/v1
kind: TaskRun
metadata:
  name: print-message-run
spec:
  taskSpec:
    params:
      - name: message
        type: string
    steps:
      - name: print
        image: ubuntu
        script: |
          echo "$(params.message)"
  params:
    - name: message
      value: "Hello, Tekton!"

Important Parameters

Timeout

Timeout allows setting a maximum duration for TaskRun execution.

Use Cases

  • Preventing long-running Tasks from consuming resources indefinitely
  • Ensuring CI/CD pipelines complete within a reasonable timeframe
  • Handling hung or deadlocked Tasks

Principles

Timeouts are:

  • Specified in the TaskRun specification
  • Applied to the entire TaskRun execution
  • Measured from the start of the first Step to the completion of the last Step
  • Result in TaskRun failure if exceeded

Configuration Example

apiVersion: tekton.dev/v1
kind: TaskRun
metadata:
  name: build-with-timeout
spec:
  taskRef:
    name: build-app
  timeout: "10m"
  params:
    - name: image
      value: my-registry/my-app:latest

Pod Template

Pod templates allow customizing the Kubernetes Pod configuration for a TaskRun.

Use Cases

  • Setting resource limits and requests
  • Configuring node selectors and tolerations
  • Adding security contexts
  • Configuring service accounts

Principles

Pod templates:

  • Are applied to the Pod created for the TaskRun
  • Can override default Pod configurations
  • Allow fine-grained control over Pod execution environment
  • Can be used to meet specific security or resource requirements

Configuration Example

apiVersion: tekton.dev/v1
kind: TaskRun
metadata:
  name: build-with-pod-template
spec:
  taskRef:
    name: build-app
  podTemplate:
    securityContext:
      runAsNonRoot: true
    nodeSelector:
      disktype: ssd

References

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