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Doc updates.
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David Wilson 6 years ago
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docs/ansible.rst
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Installation
------------
1. Thoroughly review :ref:`noteworthy_differences` and :ref:`changelog`.
1. Thoroughly review :ref:`noteworthy_differences` and :ref:`known_issues`.
2. Download and extract |mitogen_url|.
3. Modify ``ansible.cfg``:

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docs/changelog.rst
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@ -15,6 +15,116 @@ Release Notes
</style>
.. _known_issues:
Known Issues
------------
Mitogen For Ansible
~~~~~~~~~~~~~~~~~~~
* The Ansible 2.7 `reboot
<https://docs.ansible.com/ansible/latest/modules/reboot_module.html>`_ module
may require a ``pre_reboot_delay`` on systemd hosts, as insufficient time
exists for the reboot command's exit status to be reported before necessary
processes are torn down.
* On OS X when a SSH password is specified and the default connection type of
``smart`` is used, Ansible may select the Paramiko plug-in rather than
Mitogen. If you specify a password on OS X, ensure ``connection: ssh``
appears in your playbook, ``ansible.cfg``, or as ``-c ssh`` on the
command-line.
* 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
~~~~~~~~~~~~
* 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.
v0.2.4 (2018-??-??)
------------------
@ -502,75 +612,6 @@ Mitogen for Ansible
* Built-in file transfer compatible with connection delegation.
**Known Issues**
* On OS X when a SSH password is specified and the default connection type of
``smart`` is used, Ansible may select the Paramiko plug-in rather than
Mitogen. If you specify a password on OS X, ensure ``connection: ssh``
appears in your playbook, ``ansible.cfg``, or as ``-c ssh`` on the
command-line.
* 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.
* The Ansible 2.7 ``reboot`` module is not yet supported.
* 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
~~~~~~~~~~~~
@ -583,33 +624,3 @@ Core Library
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.

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