potiuk commented on code in PR #36513: URL: https://github.com/apache/airflow/pull/36513#discussion_r1440835976
########## docs/apache-airflow/core-concepts/overview.rst: ########## @@ -18,49 +18,151 @@ Architecture Overview ===================== -Airflow is a platform that lets you build and run *workflows*. A workflow is represented as a :doc:`DAG <dags>` (a Directed Acyclic Graph), and contains individual pieces of work called :doc:`tasks`, arranged with dependencies and data flows taken into account. +Airflow is a platform that lets you build and run *workflows*. A workflow is represented as a +:doc:`DAG <dags>` (a Directed Acyclic Graph), and contains individual pieces of work called +:doc:`tasks`, arranged with dependencies and data flows taken into account. .. image:: ../img/edge_label_example.png :alt: An example Airflow DAG, rendered in Graph -A DAG specifies the dependencies between Tasks, and the order in which to execute them and run retries; the Tasks themselves describe what to do, be it fetching data, running analysis, triggering other systems, or more. +A DAG specifies the dependencies between Tasks, and the order in which to execute them and run retries; +the Tasks themselves describe what to do, be it fetching data, running analysis, triggering other systems, +or more. -An Airflow installation generally consists of the following components: +Airflow components +------------------ -* A :doc:`scheduler <../administration-and-deployment/scheduler>`, which handles both triggering scheduled workflows, and submitting :doc:`tasks` to the executor to run. +Required components +................... -* An :doc:`executor <executor/index>`, which handles running tasks. In the default Airflow installation, this runs everything *inside* the scheduler, but most production-suitable executors actually push task execution out to *workers*. +Minimal Airflow installation consists of the following components: -* A *triggerer*, which executes deferred tasks - executed in an async-io event loop. +* A :doc:`scheduler <../administration-and-deployment/scheduler>`, which handles both triggering scheduled + workflows, and submitting :doc:`tasks` to the executor to run. The :doc:`executor <executor/index>`, is + a configuration property of the *scheduler*, not a separate component and runs within the scheduler + process. There are several executors available out of the box, and you can also write your own. -* A *webserver*, which presents a handy user interface to inspect, trigger and debug the behaviour of DAGs and tasks. +* A *webserver*, which presents a handy user interface to inspect, trigger and debug the behaviour of + DAGs and tasks. -* A folder of *DAG files*, read by the scheduler and executor (and any workers the executor has) +* A folder of *DAG files*, is read by the *scheduler* to figure out what tasks to run and when and to + run them. -* A *metadata database*, used by the scheduler, executor and webserver to store state. +* A *metadata database*, used by the *scheduler*, and *webserver* to store state of workflows and tasks. + Setting up a metadata database is described in :doc:`/howto/set-up-database` and is required for + Airflow to work. +Optional components +................... -Basic airflow architecture --------------------------- +There are also some optional components that are not present in the basic installation -This is the basic architecture of Airflow that you'll see in simple installations: +* Optional *worker*, which executes the tasks given to it by the scheduler. In the basic installation + worker might be part of the scheduler not a separate component. It can be run as a long running process + in the :doc:`CeleryExecutor <executor/celery>`, or as a POD in the + :doc:`KubernetesExecutor <executor/kubernetes>`. + +* Optional *triggerer*, which executes deferred tasks in an async-io event loop. In basic installation + where deferred tasks are not used, triggerer might not be present. More about deferring tasks can be + found in :doc:`/authoring-and-scheduling/deferring`. + +* Optional *dag processor*, which parses DAG files and synchronizes them into the + *metadata database* in basic installation *dag processor* might be part of the scheduler not + a separate component. + +* A folder of *DAG files*, is read by *dag processor*, *workers* and *triggerer* when they are running. + If *dag processor* is present *scheduler** does not need to read the *DAG files* directly. More about + processing DAG files can be found in :doc:`/authoring-and-scheduling/dagfile-processing` + +* Optional folder of *plugins*. Plugins are a way to extend Airflow's functionality and by placing Python + files in the plugins folder you can extend Airflow functionality (similarly as via installed packages). + Plugins are read by the *scheduler*, *dag processor*, *triggerer* and *webserver*. More about + plugins can be found in :doc:`/authoring-and-scheduling/plugins`. + +Deploying Airflow components +............................ + +All the components are Python applications that can be deployed using various deployment mechanisms. + +They deployed Python applications can have extra *installed packages* installed in their Python environment. +This is useful for example to install custom operators or sensors or extend Airflow functionality with custom +plugins. + +While Airflow can be run in a single machine and with simple installation where only *scheduler* and +*webserver* are deployed, Airflow is designed to be scalable and secure, and is able ot run in a distributed +environment - where various components can run on different machines, with different security perimeters +and can be scaled by running multiple instances of the components above. Also while single person can run and +manage Airflow installation, Airflow Deployment in more complex setup can involve various roles of users +as described in the :doc:`/security/security_model`. + +Airflow itself is agnostic to what you're running - it will happily orchestrate and run anything, +either with high-level support from one of our providers, or directly as a command using the shell +or Python :doc:`operators`. + +Architecture Diagrams +--------------------- + +The diagrams below show different ways to deploy Airflow - gradually from the simple "one machine" and +single person deployment, to a more complex deployment with separate components, separate user roles and +finally with more isolated security perimeters. + +The meaning of the different connection types in the diagrams below is as follows: + +* **brown solid lines** represent *DAG files* submission and synchronization +* **blue solid lines** represent deploying and accessing *installed packages* and *plugins* +* **black dashed lines** represent control flow of workers by the *scheduler* (via executor) +* **black solid lines** represent accessing the UI to manage execution of the workflows +* **red dashed lines** represent accessing the *metadata database* by all components + +Basic Airflow deployment +........................ + +This is the simplest deployment of Airflow, usually operated and managed on a single +machine. Such deployment usually uses Local Executor, where the *scheduler* and the *workers* are in +the same component and the *DAG files* are read directly from the local filesystem by the *scheduler* +and there is no separate *triggerer* to run deferred tasks and *webserver* runs on the same machine +as the *scheduler*. + +Such installation typically does not separate user roles - deployment, configuration, operation, authoring +and maintenance are all done by the same person and there are no security perimeters between the components. .. image:: ../img/diagram_basic_airflow_architecture.png -Most executors will generally also introduce other components to let them talk to their workers - like a task queue - but you can still think of the executor and its workers as a single logical component in Airflow overall, handling the actual task execution. +If you want to run Airflow on a single machine in a simple single-machine setup, you can skip the +more complex diagrams below and go straight to the :ref:`overview:workloads` section. + +Distributed Airflow architecture +................................ + +This is the architecture of Airflow where components of Airflow are distributed among multiple machines +and where various roles of users are introduced - **Deployment Manager**, **DAG author**, +**Operations User**. You can read more about those various roles in the :doc:`/security/security_model`. + +In case of distributed deployment, it is much more important to consider security aspects of the components. +The *webserver* does not have access to the *DAG files* directly (the code you see in the Code tab of the +UI is synchronized via the *metadata database*). This way the *webserver* cannot execute any +code submitted by **DAG author**. It can only execute code that is installed as *installed packages* or +*plugins* by the **Deployment Manager**. Also the **Operations User** has only access to the UI and can +only trigger DAGs and tasks, but cannot author DAGs. + +The *DAG files* need to be synchronized between all the components that use them - *scheduler*, +*triggerer* and *workers*. The *DAG files* can be synchronized by various mechanisms - for example by +using a shared filesystem, or by using a version control system like Git. Review Comment: I removed specific mentioning of the mechanisms - instead I linked to our helm-chart's `managing-dag-files` document that explains all the various options: ``` The *DAG files* need to be synchronized between all the components that use them - *scheduler*, *triggerer* and *workers*. The *DAG files* can be synchronized by various mechanisms - typical ways how DAGs can be synchronized are described in :doc:`helm-chart:manage-dag-files` ot our Helm Chart documentation. Helm chart is one of the ways how to deploy Airflow in K8S cluster. ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@airflow.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
