mitogen/docs/changelog.rst

.. _changelog:

Release Notes
=============


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    v0.2.3 (2018-07-??)
    -------------------

    * `#315 <https://github.com/dw/mitogen/pull/315>`_: Mitogen for Ansible is
      supported under Ansible 2.6. Contributed by `Dan Quackenbush
      <https://github.com/danquack>`_.

    * Compatible with development versions of Ansible post https://github.com/ansible/ansible/pull/41749


v0.2.3 (2018-08-??)
-------------------

Mitogen for Ansible
~~~~~~~~~~~~~~~~~~~

* `#251 <https://github.com/dw/mitogen/issues/251>`_,
  `#340 <https://github.com/dw/mitogen/issues/340>`_: Connection Delegation
  could establish connections to the wrong target when ``delegate_to:`` is
  present.

* `#291 <https://github.com/dw/mitogen/issues/291>`_: when Mitogen had
  previously been installed using ``pip`` or ``setuptools``, the globally
  installed version could conflict with a newer version bundled with an
  extension that had been installed using the documented steps. Now the bundled
  library always overrides over any system-installed copy.

* `#324 <https://github.com/dw/mitogen/issues/324>`_: plays with a custom
  ``module_utils`` would fail due to fallout from the Python 3 port and related
  tests being disabled.

* `#331 <https://github.com/dw/mitogen/issues/331>`_: fixed known issue: the
  connection multiplexer subprocess always exits before the main Ansible
  process exits, ensuring logs generated by it do not overwrite the user's
  prompt when ``-vvv`` is enabled.

* `#332 <https://github.com/dw/mitogen/issues/332>`_: support a new
  :data:`sys.excepthook`-based module exit mechanism added in Ansible 2.6.

* `#338 <https://github.com/dw/mitogen/issues/338>`_: compatibility: due to
  Ansible's implementation, changes to ``/etc/environment`` made by a task are
  reflected in the runtime environment of subsequent tasks, but only if those
  tasks set ``become: true``, or if SSH multiplexing is disabled. Changes to
  ``/etc/environment`` are now monitored and always reflected.

* Runs with many targets executed the module dependency scanner redundantly
  due to missing synchronization, causing significant wasted computation in the
  connection multiplexer subprocess. For one real-world playbook the scanner
  runtime was reduced by 95%, which may manifest as shorter runs.

* A missing check caused an exception traceback to appear when using the
  ``ansible`` command-line tool with a missing or misspelled module name.

* Ansible since >2.6 began importing ``__main__`` from
  ``ansible.module_utils.basic``, causing an error during execution, due to the
  controller being configured to refuse network imports outside the
  ``ansible.*`` namespace. Update the target implementation to construct a stub
  ``__main__`` module to satisfy the otherwise seemingly vestigial import.


Core Library
~~~~~~~~~~~~

* `#313 <https://github.com/dw/mitogen/issues/313>`_:
  :meth:`mitogen.parent.Context.call` was documented as capable of accepting
  static methods. While possible on Python 2.x the result is very ugly, and in
  every case it should be trivially possible to replace with a class method.
  The API docs were updated to remove mention of static methods.

* `#339 <https://github.com/dw/mitogen/issues/339>`_: the LXD connection method
  was erroneously executing LXC Classic commands.

* Add a :func:`mitogen.fork.on_fork` function to allow non-Mitogen managed
  process forks to clean up Mitogen resources in the forked chlid.


Thanks!
~~~~~~~

Mitogen would not be possible without the support of users. A huge thanks for
the bug reports in this release contributed by
`Rick Box <https://github.com/boxrick>`_,
`Dan Quackenbush <https://github.com/danquack>`_,
`Alex Russu <https://github.com/alexrussu>`_,
`Timo Beckers <https://github.com/ti-mo>`_,
`Jesse London <https://github.com/jesteria>`_,
`Pateek Jain <https://github.com/prateekj201>`_, and
`Pierre-Henry Muller <https://github.com/pierrehenrymuller>`_.


v0.2.2 (2018-07-26)
-------------------

Mitogen for Ansible
~~~~~~~~~~~~~~~~~~~

* `#291 <https://github.com/dw/mitogen/issues/291>`_: ``ansible_*_interpreter``
  variables are parsed using a restrictive shell-like syntax, supporting a
  common idiom where ``ansible_python_interpreter`` is set to ``/usr/bin/env
  python``.

* `#299 <https://github.com/dw/mitogen/issues/299>`_: fix the ``network_cli``
  connection type when the Mitogen strategy is active. Mitogen cannot help
  network device connections, however it should still be possible to use device
  connections while Mitogen is active.

* `#301 <https://github.com/dw/mitogen/pull/301>`_: variables like ``$HOME`` in
  the ``remote_tmp`` setting are evaluated correctly.

* `#303 <https://github.com/dw/mitogen/pull/303>`_: the :ref:`doas` become method
  is supported. Contributed by `Mike Walker
  <https://github.com/napkindrawing>`_.

* `#309 <https://github.com/dw/mitogen/issues/309>`_: fix a regression to
  process environment cleanup, caused by the change in v0.2.1 to run local
  tasks with the correct environment.

* `#317 <https://github.com/dw/mitogen/issues/317>`_: respect the verbosity
  setting when writing to Ansible's ``log_path``, if it is enabled. Child log
  filtering was also incorrect, causing the master to needlessly wake many
  times. This nets a 3.5% runtime improvement running against the local
  machine.

* The ``mitogen_ssh_debug_level`` variable is supported, permitting SSH debug
  output to be included in Mitogen's ``-vvv`` output when both are specified.


Core Library
~~~~~~~~~~~~

* `#291 <https://github.com/dw/mitogen/issues/291>`_: the ``python_path``
  parameter may specify an argument vector prefix rather than a string program
  path.

* `#300 <https://github.com/dw/mitogen/issues/300>`_: the broker could crash on
  OS X during shutdown due to scheduled `kqueue
  <https://www.freebsd.org/cgi/man.cgi?query=kevent>`_ filter changes for
  descriptors that were closed before the IO loop resumes. As a temporary
  workaround, kqueue's bulk change feature is not used.

* `#303 <https://github.com/dw/mitogen/pull/303>`_: the :ref:`doas` become method
  is now supported. Contributed by `Mike Walker
  <https://github.com/napkindrawing>`_.

* `#307 <https://github.com/dw/mitogen/issues/307>`_: SSH login banner output
  containing the word 'password' is no longer confused for a password prompt.

* `#319 <https://github.com/dw/mitogen/issues/319>`_: SSH connections would
  fail immediately on Windows Subsystem for Linux, due to use of `TCSAFLUSH`
  with :func:`termios.tcsetattr`. The flag is omitted if WSL is detected.

* `#320 <https://github.com/dw/mitogen/issues/320>`_: The OS X poller
  could spuriously wake up due to ignoring an error bit set on events returned
  by the kernel, manifesting as a failure to read from an unrelated descriptor.

* Standard IO forwarding accidentally configured the replacement ``stdout`` and
  ``stderr`` write descriptors as non-blocking, causing subprocesses that
  generate more output than kernel buffer space existed to throw errors. The
  write ends are now configured as blocking.

* When :func:`mitogen.core.enable_profiling` is active, :mod:`mitogen.service`
  threads are profiled just like other threads.

* The ``ssh_debug_level`` parameter is supported, permitting SSH debug output
  to be redirected to a Mitogen logger when specified.

* Debug logs containing command lines are printed with the minimal quoting and
  escaping required.


Thanks!
~~~~~~~

Mitogen would not be possible without the support of users. A huge thanks for
the bug reports and pull requests in this release contributed by
`Alex Russu <https://github.com/alexrussu>`_,
`Andy Freeland <https://github.com/rouge8>`_,
`Ayaz Ahmed Khan <https://github.com/ayaz>`_,
`Colin McCarthy <https://github.com/colin-mccarthy>`_,
`Dan Quackenbush <https://github.com/danquack>`_,
`Duane Zamrok <https://github.com/dewthefifth>`_,
`falbanese <https://github.com/falbanese>`_,
`Gonzalo Servat <https://github.com/gservat>`_,
`Guy Knights <https://github.com/knightsg>`_,
`Josh Smift <https://github.com/jbscare>`_,
`Mark Janssen <https://github.com/sigio>`_,
`Mike Walker <https://github.com/napkindrawing>`_,
`Tawana Musewe <https://github.com/tbtmuse>`_, and
`Zach Swanson <https://github.com/zswanson>`_.


v0.2.1 (2018-07-10)
-------------------

Mitogen for Ansible
~~~~~~~~~~~~~~~~~~~

* `#297 <https://github.com/dw/mitogen/issues/297>`_: compatibility: local
  actions set their working directory to that of their defining playbook, and
  inherit a process environment as if they were executed as a subprocess of the
  forked task worker.


v0.2.0 (2018-07-09)
-------------------

Mitogen 0.2.x is the inaugural feature-frozen branch eligible for fixes only,
except for problem areas listed as in-scope below. While stable from a
development perspective, it should still be considered "beta" at least for the
initial releases.

**In Scope**

* Python 3.x performance improvements
* Subprocess reaping improvements
* Major documentation improvements
* PyPI/packaging improvements
* Test suite improvements
* Replacement CI system to handle every supported OS
* Minor deviations from vanilla Ansible behaviour
* Ansible ``raw`` action support

The goal is a *tick/tock* model where even-numbered series are a maturation of
the previous unstable series, and unstable series are released on PyPI with
``--pre`` enabled. The API and user visible behaviour should remain unchanged
within a stable series.


Mitogen for Ansible
~~~~~~~~~~~~~~~~~~~

* Support for Ansible 2.3 - 2.5.x and any mixture of Python 2.6, 2.7 or 3.6 on
  controller and target nodes.

* Drop-in support for many Ansible connection types.

* Preview of Connection Delegation feature.

* Built-in file transfer compatible with connection delegation.


**Known Issues**

* The ``raw`` action executes as a regular Mitogen connection, which requires
  Python on the target, precluding its use for installing Python. This will be
  addressed in a future 0.2 release. For now, simply mix Mitogen and vanilla
  Ansible strategies in your playbook:

  .. code-block:: yaml

    - hosts: web-servers
      strategy: linear
      tasks:
      - name: Install Python if necessary.
        raw: test -e /usr/bin/python || apt install -y python-minimal

    - hosts: web-servers
      strategy: mitogen_linear
      roles:
      - nginx
      - initech_app
      - y2k_fix

* When running with ``-vvv``, log messages such as *mitogen: Router(Broker(0x7f5a48921590)): no route
  for Message(..., 102, ...), my ID is ...* may be visible. These are due to a
  minor race while initializing logging and can be ignored.

.. * When running with ``-vvv``, log messages will be printed to the console
     *after* the Ansible run completes, as connection multiplexer shutdown only
     begins after Ansible exits. This is due to a lack of suitable shutdown hook
     in Ansible, and is fairly harmless, albeit cosmetically annoying. A future
     release may include a solution.

.. * Configurations will break that rely on the `hashbang argument splitting
     behaviour <https://github.com/ansible/ansible/issues/15635>`_ of the
     ``ansible_python_interpreter`` setting, contrary to the Ansible
     documentation. This will be addressed in a future 0.2 release.

* Performance does not scale linearly with target count. This requires
  significant additional work, as major bottlenecks exist in the surrounding
  Ansible code. Performance-related bug reports for any scenario remain
  welcome with open arms.

* Performance on Python 3 is significantly worse than on Python 2. While this
  has not yet been investigated, at least some of the regression appears to be
  part of the core library, and should therefore be straightforward to fix as
  part of 0.2.x.

* *Module Replacer* style Ansible modules are not supported.

* Actions are single-threaded for each `(host, user account)` combination,
  including actions that execute on the local machine. Playbooks may experience
  slowdown compared to vanilla Ansible if they employ long-running
  ``local_action`` or ``delegate_to`` tasks delegating many target hosts to a
  single machine and user account.

* Connection Delegation remains in preview and has bugs around how it infers
  connections. Connection establishment will remain single-threaded for the 0.2
  series, however connection inference bugs will be addressed in a future 0.2
  release.

* Connection Delegation does not support automatic tunnelling of SSH-dependent
  actions, such as the ``synchronize`` module. This will be addressed in the
  0.3 series.


Core Library
~~~~~~~~~~~~

* Synchronous connection establishment via OpenSSH, sudo, su, Docker, LXC and
  FreeBSD Jails, local subprocesses and :func:`os.fork`. Parallel connection
  setup is possible using multiple threads. Connections may be used from one or
  many threads after establishment.

* UNIX masters and children, with Linux, MacOS, FreeBSD, NetBSD, OpenBSD and
  Windows Subsystem for Linux explicitly supported.

* Automatic tests covering Python 2.6, 2.7 and 3.6 on Linux only.


**Known Issues**

* Serialization is still based on :mod:`pickle`. While there is high confidence
  remote code execution is impossible in Mitogen's configuration, an untrusted
  context may at least trigger disproportionately high memory usage injecting
  small messages (*"billion laughs attack"*). Replacement is an important
  future priority, but not critical for an initial release.

* Child processes are not reliably reaped, leading to a pileup of zombie
  processes when a program makes many short-lived connections in a single
  invocation. This does not impact Mitogen for Ansible, however it limits the
  usefulness of the core library. A future 0.2 release will address it.

* Some races remain around :class:`mitogen.core.Broker <Broker>` destruction,
  disconnection and corresponding file descriptor closure. These are only
  problematic in situations where child process reaping is also problematic.

* The `fakessh` component does not shut down correctly and requires flow
  control added to the design. While minimal fixes are possible, due to the
  absence of flow control the original design is functionally incomplete.

* The multi-threaded :ref:`service` remains in a state of design flux and
  should be considered obsolete, despite heavy use in Mitogen for Ansible. A
  future replacement may be integrated more tightly with, or entirely replace
  the RPC dispatcher on the main thread.

* Documentation is in a state of disrepair. This will be improved over the 0.2
  series.