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Scheduling

Cloudomation supports flexible and powerful means of repeatedly running a flow.

Use Cases

Use a Schedule to

  • Execute a flow in fixed or flexible time intervals (minutes, hours, days, weeks, months, etc...),
  • Execute a flow on particular days of a calendar,
  • Execute a flow in arbitrary complex intervals,
  • Permanently poll a third party system.

Concept

Cloudomation separates

  • the logic which ensures a flow is executed repeatedly (the Scheduler)
  • the configuration how the flow should be scheduled (the Setting)
  • the logic of the flow itself (the Flow)
  • the resource which combines all this (the Schedule)
schedulesSchedulerSchedulerScheduleScheduleScheduler->ScheduleExecutionExecutionSchedule->ExecutionSettingSettingSetting->ScheduleFlowFlowFlow->Schedule

Using this separation it is possible to use the same scheduler logic (e.g. schedule something daily) for different flows with varying settings (e.g. scheduled at different hours)

note

As soon as a schedule is enabled Cloudomation will make sure that an active execution of the scheduler exists. If the scheduled execution fails or is cancelled, Cloudomation will re-start it for you.

Scheduler

A scheduler contains the script which implements logic to wait until the next iteration and start the flow.

A scheduler script should start the scheduled flow only once and then end. Cloudomation will take care to start the next iteration. In case of an error in the Scheduler script Cloudomation will wait one minute and start another iteration.

note

Cancelling a scheduled execution will also result in Cloudomation starting anther iteration after one minute. To stop the schedule, the schedule resource must be disabled or deleted.

example
import flow_api

def handler(system: flow_api.System, this: flow_api.Execution):
"""A simple scheduler script which starts the flow every minute"""

# The execution receives the IDs of the referenced setting, flow,
# and schedule resources.
# In this example we'll only use the flow_id
inputs = this.get('input_value')
flow = system.flow(inputs['flow_id'], by='id')

# wait one minute
this.sleep(60)

# start the flow
this.flow(flow.get('name'))

return this.success('all done')

Setting

The associated setting contains configuration options for the scheduler. Different schedulers can support different options. E.g. the number of minutes between two iterations, or the time at which to start the flow every day.

example
time: '09:00'
timezone: 'Europe/Vienna'
days_of_week: [1, 2, 3, 4, 5]
danger

Changing the value of a setting which is used for a schedule does not immediately reload the changed values. It is best practice to restart the schedule after making any changes by disabling and enabling it.

Flow

The flow contains the script which is repeatedly executed.

A scheduler might pass context information to the flow execution. Which inputs are passed (if any) is up to the Scheduler script. The information passed can be used to have different behaviour in different iterations or for logging/audit purposes.

Here are some examples:

  • The iteration counter
  • A flag if the current day is a public holiday
  • Email of the operator on shift

Schedule

The schedule links one scheduler with one setting and one flow. Note that using a setting is always necessary even if the scheduler does not have any configurable parameters (i.e. the whole scheduling logic is described within the scheduler). In this case you can use an empty setting. However, it is recommended that parameters are not hard-coded within schedulers but are instead stored in settings for flexibility and maintainability.

The schedule can be disabled or enabled. Once the schedule is enabled, Cloudomation will immediately start an execution of the scheduler script.

When a schedule is disabled, all currently running executions of the scheduler script are cancelled by Cloudomation.

danger

Changing fields of a schedule does not immediately reload currently running scheduler executions. It is best practice to restart the schedule after making any changes by disabling and enabling it.

Complex schedulers

A scheduler script uses the same syntax as a regular flow script. This means that a scheduler can use arbitrary complex logic, connect to third party systems, and start child executions. Some examples:

  • Connect to a calendar to check the next appointment time
  • Check a weather API when some flow should only run after rain
  • Analyse the status of other executions
  • Check an email inbox

There are two recommendations to keep in mind when designing a scheduler:

  1. Separation of concerns

    The scheduler should only contain logic needed to do the scheduling. The referenced flow on the other hand contains the logic which is scheduled.

  2. Reusability

    A scheduler should be designed so it can be used for different flows.

Considering those points the examples above should rather be placed in the Flow which is schedlued, than in the scheduler.

Example schedulers

We provide several example schedulers as part of the Scheduling bundle.

Schedule recurring

Schedule a flow to run in recurring intervals

Configuration options

  • max_iterations: int = None

    if set, the schedule will disable itself once the number of iterations is reached

  • interval_seconds: int = 60

    how many seconds to wait between iterations

  • timezone: str = 'Europe/Vienna'

    the timezone to use for timestamps

  • input_value: dict = {}

    additional inputs passed to the flow

Schedule daily

Schedule a flow to run at the same time every day

note

This scheduler will correct for DST changes of the provided timezone.

Configuration options

  • max_iterations: int = None

    if set, the schedule will disable itself once the number of iterations is reached

  • time: str = '08:15'

    the time at which the flow is started daily

  • timezone: str = 'Europe/Vienna'

    the timezone to use for timestamps

  • input_value: dict = {}

    additional inputs passed to the flow

Learn More

Executions
Webhooks
Scheduling bundle