mitogen/docs/changelog.rst

.. _changelog:

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


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

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

Enhancements
^^^^^^^^^^^^

* `#315 <https://github.com/dw/mitogen/pull/315>`_: Ansible 2.6 is supported.

* `#321 <https://github.com/dw/mitogen/issues/321>`_,
  `#336 <https://github.com/dw/mitogen/issues/336>`_: temporary file handling
  was simplified, undoing earlier damage caused by compatibility fixes,
  improving 2.6 compatibility, and avoiding two network roundtrips for every
  related action
  (`assemble <http://docs.ansible.com/ansible/latest/modules/assemble_module.html>`_,
  `aws_s3 <http://docs.ansible.com/ansible/latest/modules/aws_s3_module.html>`_,
  `copy <http://docs.ansible.com/ansible/latest/modules/copy_module.html>`_,
  `patch <http://docs.ansible.com/ansible/latest/modules/patch_module.html>`_,
  `script <http://docs.ansible.com/ansible/latest/modules/script_module.html>`_,
  `template <http://docs.ansible.com/ansible/latest/modules/template_module.html>`_,
  `unarchive <http://docs.ansible.com/ansible/latest/modules/unarchive_module.html>`_,
  `uri <http://docs.ansible.com/ansible/latest/modules/uri_module.html>`_). See
  :ref:`ansible_tempfiles` for a complete description.

* `084c0ac0 <https://github.com/dw/mitogen/commit/084c0ac0>`_: avoid a
  roundtrip in
  `copy <http://docs.ansible.com/ansible/latest/modules/copy_module.html>`_ and
  `template <http://docs.ansible.com/ansible/latest/modules/template_module.html>`_
  due to an unfortunate default.

* `7458dfae <https://github.com/dw/mitogen/commit/7458dfae>`_: avoid a
  roundtrip when transferring files smaller than 124KiB. Copy and template
  actions are now 2-RTT, reducing runtime for a 20-iteration template loop over
  a 250 ms link from 30 seconds to 10 seconds compared to v0.2.2, down from 120
  seconds compared to vanilla.

* `d62e6e2a <https://github.com/dw/mitogen/commit/d62e6e2a>`_: many-target
  runs executed the dependency scanner redundantly due to missing
  synchronization, wasting significant runtime in the connection multiplexer.
  In one case work was reduced by 95%, which may manifest as faster runs.

* `5189408e <https://github.com/dw/mitogen/commit/5189408e>`_: threads are
  cooperatively scheduled, minimizing `GIL
  <https://en.wikipedia.org/wiki/Global_interpreter_lock>`_ contention, and
  reducing context switching by an order of magnitude. This manifests as an
  overall improvement, but is easily noticeable on short many-target
  runs, where startup overhead dominates runtime.


Fixes
^^^^^

* `#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 <https://docs.ansible.com/ansible/latest/reference_appendices/config.html#default-module-utils-path>`_
  would fail due to fallout from the Python 3 port and related tests being
  disabled.

* `#331 <https://github.com/dw/mitogen/issues/331>`_: the connection
  multiplexer subprocess always exits before the main Ansible process, 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
  :func:`sys.excepthook`-based module exit mechanism added in Ansible 2.6.

* `#338 <https://github.com/dw/mitogen/issues/338>`_: compatibility: changes to
  ``/etc/environment`` and ``~/.pam_environment`` made by a task are reflected
  in the runtime environment of subsequent tasks. See
  :ref:`ansible_process_env` for a complete description.

* `#343 <https://github.com/dw/mitogen/issues/343>`_: the sudo ``--login``
  option is supported.

* `#344 <https://github.com/dw/mitogen/issues/344>`_: connections no longer
  fail when the controller's login username contains slashes.

* `#345 <https://github.com/dw/mitogen/issues/345>`_: the ``IdentitiesOnly
  yes`` option is no longer supplied to OpenSSH by default, better matching
  Ansible's behaviour.

* 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 >=2.7 began importing :mod:`__main__` from
  :mod:`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
  :mod:`__main__` module to satisfy the otherwise seemingly vestigial import.


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

* `#305 <https://github.com/dw/mitogen/issues/305>`_: fix a long-standing minor
  race relating to the logging framework, where *no route for Message(...)(*
  would appear fruequently during startup.

* `#313 <https://github.com/dw/mitogen/issues/313>`_:
  :meth:`mitogen.parent.Context.call` was accidentally documented as capable of
  accepting static methods. While possible on Python 2.x the result is ugly,
  and in every case it should be trivial to replace with a classmethod. The
  documentation was fixed.

* `#337 <https://github.com/dw/mitogen/issues/337>`_: to avoid a scaling
  limitation, SSH no longer allocates a PTY for every OpenSSH client. PTYs are
  only allocated if a password is supplied, or when `host_key_checking=accept`.
  This is since Linux has a default of 4096 PTYs (``kernel.pty.max``), while OS
  X has a default of 127 and an absolute maximum of 999
  (``kern.tty.ptmx_max``).

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

* `#345 <https://github.com/dw/mitogen/issues/345>`_: the SSH connection method
  allows optionally disabling ``IdentitiesOnly yes``.

* `af2ded66 <https://github.com/dw/mitogen/commit/af2ded66>`_: add
  :func:`mitogen.fork.on_fork` to allow non-Mitogen managed process forks to
  clean up Mitogen resources in the child.

* `d6784242 <https://github.com/dw/mitogen/commit/d6784242>`_: the setns method
  always resets ``HOME``, ``SHELL``, ``LOGNAME`` and ``USER`` environment
  variables to an account in the target container, defaulting to ``root``.

* `830966bf <https://github.com/dw/mitogen/commit/830966bf>`_: the UNIX
  listener no longer crashes if the peer process disappears in the middle of
  connection setup.

* `5adae88d <https://github.com/dw/mitogen/commit/5adae88d>`_ a new
  `mitogen_chain` keyword argument is accepted by
  :meth:`mitogen.parent.Context.call_async`, allowing overlapping chains of
  function calls to be pipelined to a context, while cancelling the chain on
  the first exception.


Thanks!
~~~~~~~

Mitogen would not be possible without the support of users. A huge thanks for
the bug reports in this release contributed by
`Alex Russu <https://github.com/alexrussu>`_,
`atoom <https://github.com/atoom>`_,
`Berend De Schouwer <https://github.com/berenddeschouwer>`_,
`Dan Quackenbush <https://github.com/danquack>`_,
`dsgnr <https://github.com/dsgnr>`_,
`Jesse London <https://github.com/jesteria>`_,
`Jonathan Rosser <https://github.com/jrosser>`_,
`Josh Smift <https://github.com/jbscare>`_,
`Luca Nunzi <https://github.com/0xlc>`_,
`nikitakazantsev12 <https://github.com/nikitakazantsev12>`_,
`Peter V. Saveliev <https://github.com/svinota>`_,
`Pierre-Henry Muller <https://github.com/pierrehenrymuller>`_,
`Pierre-Louis Bonicoli <https://github.com/jesteria>`_,
`Prateek Jain <https://github.com/prateekj201>`_,
`Rick Box <https://github.com/boxrick>`_, and
`Timo Beckers <https://github.com/ti-mo>`_.


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.

* `#342 <https://github.com/dw/mitogen/issues/342>`_: The ``network_cli``
  connection type would fail due to a missing internal SSH plugin method.

* 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 - 2.6.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 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.