Airflow - 2.8.1

Significant Changes

Target version for core dependency pendulum package set to 3 (#36281).

Support for pendulum 2.1.2 will be saved for a while, presumably until the next feature version of Airflow.
It is advised to upgrade user code to use pendulum 3 as soon as possible.

Airflow packaging specification follows modern Python packaging standards (#36537).

We standardized Airflow dependency configuration to follow latest development in Python packaging by
using pyproject.toml. Airflow is now compliant with those accepted PEPs:

• PEP-440 Version Identification and Dependency Specification <https://www.python.org/dev/peps/pep-0440/>__
• PEP-517 A build-system independent format for source trees <https://www.python.org/dev/peps/pep-0517/>__
• PEP-518 Specifying Minimum Build System Requirements for Python Projects <https://www.python.org/dev/peps/pep-0518/>__
• PEP-561 Distributing and Packaging Type Information <https://www.python.org/dev/peps/pep-0561/>__
• PEP-621 Storing project metadata in pyproject.toml <https://www.python.org/dev/peps/pep-0621/>__
• PEP-660 Editable installs for pyproject.toml based builds (wheel based) <https://www.python.org/dev/peps/pep-0660/>__
• PEP-685 Comparison of extra names for optional distribution dependencies <https://www.python.org/dev/peps/pep-0685/>__

Also we implement multiple license files support coming from Draft, not yet accepted (but supported by hatchling) PEP:
* PEP 639 Improving License Clarity with Better Package Metadata <https://peps.python.org/pep-0639/>__

This has almost no noticeable impact on users if they are using modern Python packaging and development tools, generally
speaking Airflow should behave as it did before when installing it from PyPI and it should be much easier to install
it for development purposes using pip install -e ".[devel]".

The differences from the user side are:

• Airflow extras now get extras normalized to - (following PEP-685) instead of _ and .
  (as it was before in some extras). When you install airflow with such extras (for example dbt.core or
  all_dbs) you should use - instead of _ and ..

In most modern tools this will work in backwards-compatible way, but in some old version of those tools you might need to
replace _ and . with -. You can also get warnings that the extra you are installing does not exist - but usually
this warning is harmless and the extra is installed anyway. It is, however, recommended to change to use - in extras in your dependency
specifications for all Airflow extras.

• Released airflow package does not contain devel, devel-*, doc and doc-gen extras.
  Those extras are only available when you install Airflow from sources in --editable mode. This is
  because those extras are only used for development and documentation building purposes and are not needed
  when you install Airflow for production use. Those dependencies had unspecified and varying behaviour for
  released packages anyway and you were not supposed to use them in released packages.

• The all and all-* extras were not always working correctly when installing Airflow using constraints
  because they were also considered as development-only dependencies. With this change, those dependencies are
  now properly handling constraints and they will install properly with constraints, pulling the right set
  of providers and dependencies when constraints are used.

Graphviz dependency is now an optional one, not required one (#36647).

The graphviz dependency has been problematic as Airflow required dependency - especially for
ARM-based installations. Graphviz packages require binary graphviz libraries - which is already a
limitation, but they also require to install graphviz Python bindings to be build and installed.
This does not work for older Linux installation but - more importantly - when you try to install
Graphviz libraries for Python 3.8, 3.9 for ARM M1 MacBooks, the packages fail to install because
Python bindings compilation for M1 can only work for Python 3.10+.

This is not a breaking change technically - the CLIs to render the DAGs is still there and IF you
already have graphviz installed, it will continue working as it did before. The only problem when it
does not work is where you do not have graphviz installed it will raise an error and inform that you need it.

Graphviz will remain to be installed for most users:

• the Airflow Image will still contain graphviz library, because
  it is added there as extra
• when previous version of Airflow has been installed already, then
  graphviz library is already installed there and Airflow will
  continue working as it did

The only change will be a new installation of new version of Airflow from the scratch, where graphviz will
need to be specified as extra or installed separately in order to enable DAG rendering option.

Bug Fixes

• Fix airflow-scheduler exiting with code 0 on exceptions (#36800)
• Fix Callback exception when a removed task is the last one in the taskinstance list (#36693)
• Allow anonymous user edit/show resource when set AUTH_ROLE_PUBLIC=admin (#36750)
• Better error message when sqlite URL uses relative path (#36774)
• Explicit string cast required to force integer-type run_ids to be passed as strings instead of integers (#36756)
• Add log lookup exception for empty op subtypes (#35536)
• Remove unused index on task instance (#36737)
• Fix check on subclass for typing.Union in _infer_multiple_outputs for Python 3.10+ (#36728)
• Make sure multiple_outputs is inferred correctly even when using TypedDict (#36652)
• Add back FAB constant in legacy security manager (#36719)
• Fix AttributeError when using Dagrun.update_state (#36712)
• Do not let EventsTimetable schedule past events if catchup=False (#36134)
• Support encryption for triggers parameters (#36492)
• Fix the type hint for tis_query in _process_executor_events (#36655)
• Redirect to index when user does not have permission to access a page (#36623)
• Avoid using dict as default value in call_regular_interval (#36608)
• Remove option to set a task instance to running state in UI (#36518)
• Fix details tab not showing when using dynamic task mapping (#36522)
• Raise error when DagRun fails while running dag test (#36517)
• Refactor _manage_executor_state by refreshing TIs in batch (#36502)
• Add flask config: MAX_CONTENT_LENGTH (#36401)
• Fix get_leaves calculation for teardown in nested group (#36456)
• Stop serializing timezone-naive datetime to timezone-aware datetime with UTC tz (#36379)
• Make kubernetes decorator type annotation consistent with operator (#36405)
• Fix Webserver returning 500 for POST requests to api/dag/*/dagrun from anonymous user (#36275)
• Fix the required access for get_variable endpoint (#36396)
• Fix datetime reference in DAG.is_fixed_time_schedule (#36370)
• Fix AirflowSkipException message raised by BashOperator (#36354)
• Allow PythonVirtualenvOperator.skip_on_exit_code to be zero (#36361)
• Increase width of execution_date input in trigger.html (#36278)
• Fix logging for pausing DAG (#36182)
• Stop deserializing pickle when enable_xcom_pickling is False (#36255)
• Check DAG read permission before accessing DAG code (#36257)
• Enable mark task as failed/success always (#36254)
• Create latest log dir symlink as relative link (#36019)
• Fix Python-based decorators templating (#36103)

Miscellaneous

• Rename concurrency label to max active tasks (#36691)
• Restore function scoped httpx import in file_task_handler for performance (#36753)
• Add support of Pendulum 3 (#36281)
• Standardize airflow build process and switch to Hatchling build backend (#36537)
• Get rid of pyarrow-hotfix for CVE-2023-47248 (#36697)
• Make graphviz dependency optional (#36647)
• Announce MSSQL support end in Airflow 2.9.0, add migration script hints (#36509)
• Set min pandas dependency to 1.2.5 for all providers and airflow (#36698)
• Bump follow-redirects from 1.15.3 to 1.15.4 in /airflow/www (#36700)
• Provide the logger_name param to base hook in order to override the logger name (#36674)
• Fix run type icon alignment with run type text (#36616)
• Follow BaseHook connection fields method signature in FSHook (#36444)
• Remove redundant docker decorator type annotations (#36406)
• Straighten typing in workday timetable (#36296)
• Use batch_is_authorized_dag to check if user has permission to read DAGs (#36279)
• Replace deprecated get_accessible_dag_ids and use get_readable_dags in get_dag_warnings (#36256)

Doc Only Changes

• Metrics tagging documentation (#36627)
• In docs use logical_date instead of deprecated execution_date (#36654)
• Add section about live-upgrading Airflow (#36637)
• Replace numpy example with practical exercise demonstrating top-level code (#35097)
• Improve and add more complete description in the architecture diagrams (#36513)
• Improve the error message displayed when there is a webserver error (#36570)
• Update dags.rst with information on DAG pausing (#36540)
• Update installation prerequisites after upgrading to Debian Bookworm (#36521)
• Add description on the ways how users should approach DB monitoring (#36483)
• Add branching based on mapped task group example to dynamic-task-mapping.rst (#36480)
• Add further details to replacement documentation (#36485)
• Use cards when describing priority weighting methods (#36411)
• Update metrics.rst for param dagrun.schedule_delay (#36404)
• Update admonitions in Python operator doc to reflect sentiment (#36340)
• Improve audit_logs.rst (#36213)
• Remove Redshift mention from the list of managed Postgres backends (#36217)