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Pause, resume, and rerun a workflow

You can usepd.flow.suspend andpd.flow.rerun to pause a workflow and resume it later.This is useful when you want to:
  • Pause a workflow until someone manually approves it
  • Poll an external API until some job completes, and proceed with the workflow when it’s done
  • Trigger an external API to start a job, pause the workflow, and resume it when the external API sends an HTTP callback
We’ll cover all of these examples below.

pd.flow.suspend

Usepd.flow.suspend when you want to pause a workflow and proceed with the remaining steps only when manually approved or cancelled.For example, you can suspend a workflow and send yourself a link to manually resume or cancel the rest of the workflow:
def handler(pd:'pipedream'):    urls= pd.flow.suspend()    pd.send.email(      subject="Please approve this important workflow",      text=f"Click here to approve the workflow: ${urls["resume_url"]}, and cancel here: ${urls["cancel_url"]}"    )    # Pipedream suspends your workflow at the end of the step
You’ll receive an email like this:
And can resume or cancel the rest of the workflow by clicking on the appropriate link.

resume_url andcancel_url

In general, callingpd.flow.suspend returns acancel_url andresume_url that lets you cancel or resume paused executions. Since Pipedream pauses your workflow at theend of the step, you can pass these URLs to any external service before the workflow pauses. If that service accepts a callback URL, it can trigger theresume_url when its work is complete.These URLs are specific to a single execution of your workflow. While the workflow is paused, you can load these in your browser or send any HTTP request to them:
  • Sending an HTTP request to thecancel_url will cancel that execution
  • Sending an HTTP request to theresume_url will resume that execution
If you resume a workflow, any data sent in the HTTP request is passed to the workflow and returned in the$resume_datastep export of the suspended step. For example, if you callpd.flow.suspend within a step namedcode, the$resume_data export should contain the data sent in theresume_url request:

Default timeout of 24 hours

By default,pd.flow.suspend will automatically cancel the workflow after 24 hours. You can set your own timeout (in milliseconds) as the first argument:
def handler(pd:'pipedream'):    # 7 days    TIMEOUT = 1000 * 60 * 60 * 24 * 7    pd.flow.suspend(TIMEOUT)

pd.flow.rerun

Usepd.flow.rerun when you want to run a specific step of a workflow multiple times. This is useful when you need to start a job in an external API and poll for its completion, or have the service call back to the step and let you process the HTTP request within the step.

Polling for the status of an external job

Sometimes you need to poll for the status of an external job until it completes.pd.flow.rerun lets you rerun a specific step multiple times:
import requestsdef handler(pd:'pipedream'):  MAX_RETRIES = 3  # 10 seconds  DELAY = 1000 * 10  run= pd.context['run']  print(pd.context)  # pd.context.run.runs starts at 1 and increments when the step is rerun  if run['runs']== 1:    # pd.flow.rerun(delay, context (discussed below), max retries)    pd.flow.rerun(DELAY,None,MAX_RETRIES)  elif run['runs']== MAX_RETRIES + 1:    raise Exception("Max retries exceeded")  else:    # Poll external API for status    response= requests.get("https://example.com/status")    # If we're done, continue with the rest of the workflow    if response.json().status== "DONE":      return response.json()    # Else retry later    pd.flow.rerun(DELAY,None,MAX_RETRIES)
pd.flow.rerun accepts the following arguments:
pd.flow.rerun(  delay,# The number of milliseconds until the step will be rerun  context,# JSON-serializable data you need to pass between runs  maxRetries,# The total number of times the step will rerun. Defaults to 10)

Accept an HTTP callback from an external service

When you trigger a job in an external service, and that service can send back data in an HTTP callback to Pipedream, you can process that data within the same step usingpd.flow.retry:
import requestsdef handler(pd:'pipedream'):  TIMEOUT = 86400 * 1000  run= pd.context['run']  # pd.context['run']['runs'] starts at 1 and increments when the step is rerun  if run['runs']== 1:    links= pd.flow.rerun(TIMEOUT,None,1)    # links contains a dictionary with two entries: resume_url and cancel_url    # Send resume_url to external service    await request.post("your callback URL",json=links)  # When the external service calls back into the resume_url, you have access to  # the callback data within pd.context.run['callback_request']  elif 'callback_request' in run:    return run['callback_request']

Passingcontext topd.flow.rerun

Within a Python code step,pd.context.run.context contains thecontext passed from the prior call torerun. This lets you pass data from one run to another. For example, if you call:
pd.flow.rerun(1000, {"hello": "world" })
pd.context.run.context will contain:

maxRetries

By default,maxRetries is10.When you exceedmaxRetries, the workflow proceeds to the next step. If you need to handle this case with an exception,raise an Exception from the step:
def handler(pd:'pipedream'):  MAX_RETRIES = 3  run= pd.context['run']  if run['runs']== 1:    pd.flow.rerun(1000,None,MAX_RETRIES)  else if (run['runs']== MAX_RETRIES + 1):    raise Exception("Max retries exceeded")

Behavior when testing

When you’re building a workflow and test a step withpd.flow.suspend orpd.flow.rerun, it will not suspend the workflow, and you’ll see a message like the following:
Workflow execution canceled — this may be due topd.flow.suspend() usage (not supported in test)
These functions will only suspend and resume when run in production.

Credits usage when usingpd.flow.suspend /pd.flow.rerun

You are not charged for the time your workflow is suspended during apd.flow.suspend orpd.flow.rerun. Only when workflows are resumed will compute time count towardcredit usage.
When a suspended workflow reawakens, it will reset the credit counter.Each rerun or reawakening from a suspension will count as a new fresh credit.
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