Control the order of execution in a workflow

This page shows you how to use jumps or for loops to control the order in which your workflow's steps run. Basic jumps allow you to define which step the workflow runs next. Conditional jumps build on basic jumps, allowing you to use conditional expressions to control the order of execution through a workflow. For example, you can run certain steps only when a variable or response from another workflow step meets specific criteria.

The examples on this page use a sample API that returns the day of the week.

Before you begin

  1. Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.
  2. In the Google Cloud Console, on the project selector page, select or create a Google Cloud project.

    Go to project selector

  3. Make sure that billing is enabled for your Cloud project. Learn how to confirm that billing is enabled for your project.

  4. In the Google Cloud Console, on the project selector page, select or create a Google Cloud project.

    Go to project selector

  5. Make sure that billing is enabled for your Cloud project. Learn how to confirm that billing is enabled for your project.

  6. You should already have an existing workflow where you want to change the order of execution. To learn how to create and deploy a workflow, see Create and update a workflow.

Use jumps to change execution order

By default, all workflows are ordered lists where every step runs in the order you define in the workflow's source code. You can choose to override this default ordering by using jumps.

Basic jumps

You can specify which step to run next in a workflow by using basic jumps.

Console

  1. Open the Workflows page in the Google Cloud Console:
    Go to Workflows

  2. Select the name of the workflow where you want to change the order of execution of the existing steps.

  3. On the Edit workflow page, select Next to go to the workflow editor.

  4. Add the next field at the end of a step to tell the workflow to jump to a particular step:

    YAML

         - step_a:
             ...
             next: STEP_NAME_TO_JUMP_TO
         - step_b:
             ...
         - next_step:
             ...

    JSON

        [
          {
            "step_a": {
              ...
              "next": "STEP_NAME_TO_JUMP_TO"
            }
          }
          {
            "step_b": {
              ...
            }
          }
          {
            "next_step": {
              ...
            }
          }
        ]

    Replace STEP_NAME_TO_JUMP_TO with the name of the step you want the workflow to execute next. For example, next_step.

  5. Select Deploy.

gcloud

  1. Open your workflow's definition file in the text editor of your choice.

  2. Add the next field at the end of a step to tell the workflow to jump to a particular step:

    YAML

         - step_a:
             ...
             next: STEP_NAME_TO_JUMP_TO
         - step_b:
             ...
         - next_step:
             ...

    JSON

      [
        {
          "step_a": {
            ...
            "next": "STEP_NAME_TO_JUMP_TO"
          }
        }
        {
          "step_b": {
            ...
          }
        }
        {
          "next_step": {
            ...
          }
        }
      ]

    Replace STEP_NAME_TO_JUMP_TO with the name of the step you want the workflow to execute next. For example, next_step.

  3. Save the workflow file.

  4. To deploy the workflow, enter the following command:

    gcloud workflows deploy WORKFLOW_NAME \
    --source=WORKFLOW_FILE.YAML
    

    Replace the following:

    • WORKFLOW_NAME: Required. The name of your workflow.

    • WORKFLOW_FILE.YAML: Required. The source file for the workflow.

Example

For example, the following workflow has its steps out of order:

YAML

  - get_time:
     call: http.get
     args:
         url:  https://us-central1-workflowsample.cloudfunctions.net/datetime
     result: currentTime
  - return_daylight_savings_bool:
     return: ${daylightSavings}
  - get_daylight_savings_bool:
     assign:
         - daylightSavings: ${currentTime.body.isDayLightSavingsTime}

JSON

    [
      {
        "get_time": {
          "call": "http.get",
          "args": {
            "url": "https://us-central1-workflowsample.cloudfunctions.net/datetime"
          },
          "result": "currentTime"
        }
      },
      {
        "return_daylight_savings_bool": {
          "return": "${daylightSavings}"
        }
      },
      {
        "get_daylight_savings_bool": {
          "assign": [
            {
              "daylightSavings": "${currentTime.body.isDayLightSavingsTime}"
            }
          ]
        }
      }
    ]

In this example, next fields have been added to the get_daylight_savings_bool and return_daylight_savings_bool steps so that the steps execute in the correct order:

YAML

  - get_time:
     call: http.get
     args:
         url:  https://us-central1-workflowsample.cloudfunctions.net/datetime
     result: currentTime
     next: get_daylight_savings_bool
  - return_daylight_savings_bool:
     return: ${daylightSavings}
  - get_daylight_savings_bool:
     assign:
         - daylightSavings: ${currentTime.body.isDayLightSavingsTime}
     next: return_daylight_savings_bool

JSON

    [
      {
        "get_time": {
          "call": "http.get",
          "args": {
            "url": "https://us-central1-workflowsample.cloudfunctions.net/datetime"
          },
          "result": "currentTime",
          "next": "get_daylight_savings_bool"
        }
      },
      {
        "return_daylight_savings_bool": {
          "return": "${daylightSavings}"
        }
      },
      {
        "get_daylight_savings_bool": {
          "assign": [
            {
              "daylightSavings": "${currentTime.body.isDayLightSavingsTime}"
            }
          ],
          "next": "return_daylight_savings_bool"
        }
      }
    ]

Conditional jumps

You can use conditional jumps to determine which step to run next in a workflow. Conditional jumps use switch blocks, which jump to a specified step if a particular condition is met. Each switch block can include a maximum of 10 conditions.

Console

  1. Open the Workflows page in the Google Cloud Console:
    Go to Workflows

  2. Select the name of the workflow to which you want to add a switch block.

  3. On the Edit workflow page, select Next to go to the workflow editor.

  4. On the Define workflow page, your workflow's current definition is displayed. To edit the workflow so that it executes a certain step based on a conditional statement, add a step that uses a switch block:

    YAML

         - SWITCH_STEP_NAME:
             switch:
                 - condition: ${EXPRESSION_ONE}
                   next: STEP_A
                 - condition: ${EXPRESSION_TWO}
                   next: STEP_B
                 ...
             next: STEP_C
         - STEP_A
             ...
         - STEP_B
             ...
         - STEP_C
             ...

    JSON

        [
          {
            "SWITCH_STEP_NAME": {
              "switch": [
                {
                  "condition": "${EXPRESSION_ONE}",
                  "next": "STEP_A"
                },
                {
                  "condition": "${EXPRESSION_TWO}",
                  "next": "STEP_B"
                }
              ],
              "next": "STEP_C"
            }
            "STEP_A": {
              ...
            }
            "STEP_B": {
              ...
            }
            "STEP_C": {
              ...
            }
          }
        ]

    Replace the following:

    • SWITCH_STEP_NAME: The name of the step containing the switch block.

    • EXPRESSION_ONE: The first expression to evaluate. If this expression evaluates to true, the workflow executes STEP_A next. If this expression evaluates to false, the workflow evaluates the next expression.

    • EXPRESSION_TWO: The second expression to evaluate. If this expression evaluates to true, the workflow executes STEP_B next. If this expression evaluates to false, the workflow executes STEP_C.

    • STEP_A, STEP_B, STEP_C: Placeholder step names.

  5. Select Deploy.

gcloud

  1. Open your workflow's definition in the text editor of your choice.

  2. To edit the workflow so that it executes a certain step based on a conditional statement, add a step that uses a switch block:

    YAML

     - SWITCH_STEP_NAME:
         switch:
             - condition: ${EXPRESSION_ONE}
               next: STEP_A
             - condition: ${EXPRESSION_TWO}
               next: STEP_B
             ...
         next: STEP_C
     - STEP_A
         ...
     - STEP_B
         ...
     - STEP_C
         ...
    

    JSON

    [
      {
        "SWITCH_STEP_NAME": {
          "switch": [
            {
              "condition": "${EXPRESSION_ONE}",
              "next": "STEP_A"
            },
            {
              "condition": "${EXPRESSION_TWO}",
              "next": "STEP_B"
            }
          ],
          "next": "STEP_C"
        }
        "STEP_A": {
          ...
        }
        "STEP_B": {
          ...
        }
        "STEP_C": {
          ...
        }
      }
    ]
      

    Replace the following:

    • SWITCH_STEP_NAME: The name of the step containing the switch block.

    • EXPRESSION_ONE: The first expression to evaluate. If this expression evaluates to true, the workflow executes STEP_A next. If this expression evaluates to false, the workflow evaluates the next expression.

    • EXPRESSION_TWO: The second expression to evaluate. If this expression evaluates to true, the workflow executes STEP_B next. If this expression evaluates to false, the workflow executes STEP_C.

    • STEP_A, STEP_B, STEP_C: Placeholder step names.

  3. Save the workflow file.

  4. To deploy the workflow, enter the following command:

    gcloud workflows deploy WORKFLOW_NAME \
    --source=WORKFLOW_FILE.YAML
    

    Replace the following:

    • WORKFLOW_NAME: Required. The name of your workflow.

    • WORKFLOW_FILE.YAML: Required. The source file for the workflow.

Example

For example, this workflow uses a switch block to control the workflow's order of execution:

YAML

  - getCurrentTime:
      call: http.get
      args:
          url:  https://us-central1-workflowsample.cloudfunctions.net/datetime
      result: currentTime
  - conditionalSwitch:
      switch:
          - condition: ${currentTime.body.dayOfTheWeek == "Friday"}
            next: friday
          - condition: ${currentTime.body.dayOfTheWeek == "Saturday" OR currentTime.body.dayOfTheWeek == "Sunday"}
            next: weekend
      next: workWeek
  - friday:
      return: "It's Friday! Almost the weekend!"
  - weekend:
      return: "It's the weekend!"
  - workWeek:
      return: "It's the work week."
    

JSON

    [
      {
        "getCurrentTime": {
          "call": "http.get",
          "args": {
            "url": "https://us-central1-workflowsample.cloudfunctions.net/datetime"
          },
          "result": "currentTime"
        }
      },
      {
        "conditionalSwitch": {
          "switch": [
            {
              "condition": "${currentTime.body.dayOfTheWeek == "Friday"}",
              "next": "friday"
            },
            {
              "condition": "${currentTime.body.dayOfTheWeek == "Saturday" OR currentTime.body.dayOfTheWeek == "Sunday"}",
              "next": "weekend"
            }
          ],
          "next": "workWeek"
        }
      },
      {
        "friday": {
          "return": "It's Friday! Almost the weekend!"
        }
      },
      {
        "weekend": {
          "return": "It's the weekend!"
        }
      },
      {
        "workWeek": {
          "return": "It's the work week."
        }
      }
    ]
      

In this example, the switch block has two conditions. The parser evaluates each condition in order, and if the result of the condition's expression is true, that condition's next step is called. If none of the conditions are met, the workflow calls the step specified by the next field outside of the switch block, which, in this example, is the step workWeek.

For example, if the day of the week is "Saturday", then the workflow jumps to the step weekend and returns the message "It's the weekend!". The workflow doesn't execute the step friday because the conditional jump skips over it, and the workflow doesn't execute the step workWeek because return stops the execution of the workflow at the end of the weekend step.

Use for loops to iterate

You can use for loops to iterate over a sequence of numbers or through a collection of data, such as a list or map.

You can walk through every item in a list or map using item-based iteration. If you have a specific range of numeric values to iterate through, you can use range-based iteration.

For more information and examples, see the syntax reference on iteration.

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