Understand Flows: The Core Units of Kestra Orchestration

A flow is a container for tasks and their orchestration logic.

Components of a flow

A flow organizes tasks, their inputs and outputs, error handling, and orchestration logic. It specifies what tasks run, when they run, and how they interact (sequentially, in parallel, or conditionally).

Flows are defined declaratively in YAML or built using the No Code editor.

A flow must have:

• identifier (id)
• namespace
• list of tasks

Optionally, a flow can also have:

• inputs: typed parameters passed at execution time
• outputs: values or files a flow produces for downstream use
• variables: reusable key/value pairs scoped to the flow
• triggers: schedule or event conditions that start executions automatically
• labels: key/value metadata for filtering and grouping executions
• errors: tasks that run when a flow or task fails
• finally: tasks that always run at the end, regardless of execution outcome
• retries: automatic retry policy on task failure
• sla: time-based constraints that fail or alert when exceeded
• concurrency: limits on how many executions of this flow can run simultaneously
• descriptions: Markdown documentation attached to flows and tasks
• disabled: prevent a flow from executing without deleting it
• checks: assertions that must pass before an execution is created

Flow sample

The example below uses several of the optional components listed above; refer to each component’s documentation for full configuration details.

id: hello-world
namespace: company.team

description: flow **documentation** in *Markdown*

labels:
  env: prod
  team: engineering

inputs:
  - id: my-value
    type: STRING
    defaults: "default value"
    description: This input has a default value.

variables:
  first: "1"
  second: "{{ vars.first }} > 2"

tasks:
  - id: hello
    type: io.kestra.plugin.core.log.Log
    description: "Log the input value passed at execution time."
    message: "Hello, {{ inputs.['my-value'] }}!"

  - id: date
    type: io.kestra.plugin.core.debug.Return
    description: "Return the current date as a task output."
    format: "{{ taskrun.startDate }}"

outputs:
  - id: execution_date
    type: STRING
    value: "{{ outputs.date.value }}"

triggers:
  - id: daily
    type: io.kestra.plugin.core.trigger.Schedule
    cron: "0 9 * * *"

Revision

Every change to a flow creates a new revision. Kestra automatically manages revisions, similar to version control, and you can view them in the Revisions tab.

Save as draft stages changes without affecting running executions. Draft revisions are not executed: any trigger or manual run falls back to the last published revision until you publish the draft. See Draft revisions for details.

Flow variable expressions

See also

• Synchronize Local Flows
• Sync Flows from a Git Repository
• Draft revisions
• Namespace Files