1 Meet Apache Airflow

Modern organizations are increasingly data-driven, moving vast amounts of information through pipelines that must be reliable, observable, and scalable. This chapter introduces Apache Airflow as an orchestration tool—more like a conductor than a musician—that coordinates work across many systems without doing the heavy data processing itself. It frames pipelines as directed acyclic graphs (DAGs) of tasks, explains why this abstraction is powerful for managing dependencies and execution order, and sets expectations for a hands-on, example-led journey that helps readers decide whether Airflow fits their use cases and how to get started.

Representing pipelines as DAGs turns implicit task order into explicit dependencies, enabling safe, repeatable execution without circular deadlocks. Compared with monolithic scripts, DAGs allow parallelism where tasks are independent, faster recovery by rerunning only failed pieces, and clearer reasoning about complex workflows. The chapter situates Airflow within the broader ecosystem of workflow managers, noting common capabilities and key differences in how tools define workflows (code vs. static files) and in features such as scheduling and monitoring. Airflow’s code-first approach—primarily in Python—offers strong flexibility, dynamic DAG construction, and a large ecosystem of integrations for databases, big data platforms, and cloud services.

Airflow lets you schedule DAGs on time-based or event-like schedules, then uses core components (DAG processing, scheduling, workers, and asynchronous triggers) to queue and run tasks in the right order, capturing results and logs for inspection in a rich web interface. Built-in retries, easy task reruns, and powerful time semantics support incremental processing and backfilling, making it efficient to build and maintain production pipelines. The chapter closes with guidance on fit: Airflow excels at batch and regularly scheduled or event-triggered workflows that integrate many systems and benefit from software engineering best practices; it is less suited to real-time streaming, highly volatile DAG structures, or teams without Python expertise. It also previews the rest of the book, from foundational concepts to advanced patterns and deployment guidance.

For this weather dashboard, weather data is fetched from an external API and fed into a dynamic dashboard.

Graph representation of the data pipeline for the weather dashboard. Nodes represent tasks and directed edges represent dependencies between tasks (with an edge pointing from task 1 to task 2, indicating that task 1 needs to be run before task 2).

Cycles in graphs prevent task execution due to circular dependencies. In acyclic graphs (top), there is a clear path to execute the three different tasks. However, in cyclic graphs (bottom), there is no longer a clear execution path due to the interdependency between tasks 2 and 3.

Using the DAG structure to execute tasks in the data pipeline in the correct order: depicts each task’s state during each of the loops through the algorithm, demonstrating how this leads to the completed execution of the pipeline (end state)

Overview of the umbrella demand use case, in which historical weather and sales data are used to train a model that predicts future sales demands depending on weather forecasts

Independence between sales and weather tasks in the graph representation of the data pipeline for the umbrella demand forecast model. The two sets of fetch/cleaning tasks are independent as they involve two different data sets (the weather and sales data sets). This independence is indicated by the lack of edges between the two sets of tasks.

Airflow pipelines are defined as DAGs using Python code in DAG files. Each DAG file typically defines one DAG, which describes the different tasks and their dependencies. Besides this, the DAG also defines a schedule interval that determines when the DAG is executed by Airflow.

The main components involved in Airflow are the Airflow API server, scheduler, DAG processor, triggerer and workers.

Developing and executing pipelines as DAGs using Airflow. Once the user has written the DAG, the DAG Processor and scheduler ensure that the DAG is run at the right moment. The user can monitor progress and output while the DAG is running at all times.

The login page for the Airflow web interface. In the code examples accompanying this book, a default user “airflow” is provided with the password “airflow”.

The main page of Airflow’s web interface, showing a high-level overview of all DAGs and their recent results.

The DAGs page of Airflow’s web interface, showing a high-level overview of all DAGs and their recent results.

The graph view in Airflow’s web interface, showing an overview of the tasks in an individual DAG and the dependencies between these tasks

Airflow’s grid view, showing the results of multiple runs of the umbrella sales model DAG (most recent + historical runs). The columns show the status of one execution of the DAG and the rows show the status of all executions of a single task. Colors (which you can see in the e-book version) indicate the result of the corresponding task. Users can also click on the task “squares” for more details about a given task instance, or to manage the state of a task so that it can be rerun by Airflow, if desired.x

• Directed Acyclic Graphs (DAGs) are a visual tool used to represent data workflows in data processing pipelines. A node in a DAG denote the task to be performed, and edges define the dependencies between them. This is not only visually more understandable but also aids in better representation, easier debugging + rerunning, and making use of parallelism compared to single monolithic scripts.
• In Airflow, DAGs are defined using Python files. Airflow 3.0 introduced the option of using other languages. In this book we will focus on Python. These scripts outline the order of task execution and their interdependencies. Airflow parses these files to construct and understand the DAG's structure, enabling task orchestration and scheduling.
• Although many workflow managers have been developed over the years for executing graphs of tasks, Airflow has several key features that makes it uniquely suited for implementing efficient, batch-oriented data pipelines.
• Airflow excels as a workflow orchestration tool due to its intuitive design, scheduling capabilities, and extensible framework. It provides a rich user interface for monitoring and managing tasks in data processing workflows.
• Airflow is comprised of five key components:
1. DAG Processor: Reads and parses the DAGs and stores the resulting serialized version of these DAGs in the Metastore for use by (among others) the scheduler
2. Scheduler: Reads the DAGs parsed by the DAG Processor, determines if their schedule intervals have elapsed, and queues their tasks for execution.
3. Worker: Execute the tasks assigned to them by the scheduler.
4. Triggerer: It handles the execution of deferred tasks, which are waiting for external events or conditions.
5. API Server: Among other things, presents a user interface for visualizing and monitoring the DAGs and their execution status. The API Server also acts as the interface between all Airflow components
• Airflow enables the setting of a schedule for each DAG, specifying when the pipeline should be executed. In addition, Airflow’s built-in mechanisms are able to manage task failures, automatically.
• Airflow is well-suited for batch-oriented data pipelines, offering sophisticated scheduling options that enable regular, incremental data processing jobs. On the other hand, Airflow is not the right choice for streaming workloads or for implementing highly dynamic pipelines where DAG structure changes from one day to the other.

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