# Flow ## Overview Flows enable you to coordinate the execution of multiple steps across several elements. A step can be: - A task execution - A common tool (such as sleep) - Another flow execution (referred to as a child flow) ## Schedule You can configure a specific schedule for your flow. When scheduled, the flow executes automatically on the specified days at the specified time. ## Execution Mode ### Serial In Serial mode, the flow executes all steps for a single element before moving to the next element. This ensures that each element completes its entire workflow sequentially. ### Parallel In Parallel mode, the flow executes one step across all elements before proceeding to the next step. This allows for simultaneous execution across multiple elements. ## Processing Script The Processing Script allows you to sort and filter the elements that will be used in the flow execution as you wish. ### Example ```python sort_function = lambda x: 1 if x['context']['patroni_leader'] == 'master' else 0 order_flow_elements(elements, sort_function, reverse=False) ``` This code sorts elements from DESC to ASC based on whether they are "master" or not. ### Available Variables and Functions 1. **elements**: Contains all elements that match the profile, groups, and filters 2. **order_flow_elements**: Sorts elements based on specified criteria (you can use element context) 3. **filter_flow_elements**: Filters elements based on specified criteria (you can use element context) ## Execution Script The Execution Script defines which steps will be executed when the flow runs. See [Visual Script Editing](https://docs.zequenze.com/books/flux/chapter/scripts-with-visualization-feature) to learn how to use the visual view. ### Special Variables - **elements**: The list of elements after the processing script has been applied - **current**: The number of the element currently being executed - **first**: The number of the element that will be executed first - **last**: The number of the element that will be executed last ### Custom Steps - **Filter elements** (filter_flow_elements): Filters elements and returns a list containing only the elements that match the filter criteria ## Execution Examples You can combine multiple flows of different execution modes (Serial and Parallel) to achieve more complex logic. When defining a flow execution script, you can pass specific elements to each child flow execution. ### Example Scenario Given 2 elements (E1, E2), 2 flows (F1 & F2), and 5 tasks (A, B, C, D, F): image.png ### Parent Serial - Child Serial What happens when F1 is Serial and F2 is Serial? image.png ### Parent Serial - Child Parallel What happens when F1 is Serial and F2 is Parallel? image.png ### Parent Parallel - Child Serial What happens when F1 is Parallel and F2 is Serial? image.png ### Parent Parallel - Child Parallel What happens when F1 is Parallel and F2 is Parallel? image.png