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@ -921,6 +921,154 @@ logging is necessary. File-based logging can be enabled by setting
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enabled, one file per context will be created on the local machine and every
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target machine, as ``/tmp/mitogen.<pid>.log``.
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Common Problems
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~~~~~~~~~~~~~~~
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The most common bug reports fall into the following categories, so it is worth
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checking whether you can categorize a problem using the tools provided before
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reporting it:
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**Missed/Incorrect Configuration Variables**
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In some cases Ansible may support a configuration variable that Mitogen
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does not yet support, or Mitogen supports, but the support is broken. For
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example, Mitogen may pick the wrong username or SSH parameters.
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To detect this, use the special ``mitogen_get_stack`` action described
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below to verify all the configuration variables Mitogen has chosen for the
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connection make sense.
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**Process Environment Differences**
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Mitogen's process model differs significantly to Ansible's in certain
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places. In the past, bugs have been reported because Ansible plug-ins
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modify an environment variable after Mitogen processes are started
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**Variable Expansion Differences**
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To avoid many classes of bugs, Mitogen avoids shell wherever possible.
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Ansible however is traditionally built on shell, and it is often difficult
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to tell just how many times a configuration parameter will pass through
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shell expansion and quoting, and in what context before it is used.
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Due to this, in some circumstances Mitogen may parse some expanded
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variables differently, for example, in the wrong user account. Careful
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review of ``-vvv`` and ``mitogen_ssh_debug_level`` logs can reveal this.
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For example in the past, Mitogen used a different method of expanding
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``~/.ssh/id_rsa``, causing authentication to fail when ``ansible-playbook``
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was run via ``sudo -E``.
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**External Tool Integration Differences**
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Mitogen reimplements any aspect of Ansible that involves integrating with
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SSH, sudo, Docker, or related tools. For this reason, sometimes its support
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for those tools doffers or is less mature than in Ansible.
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In the past Mitogen has had bug reports due to failing to recognize a
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particular variation of a login or password prompt on an exotic or
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non-English operating system, or confusing a login banner for a password
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prompt. Careful review of ``-vvv`` logs help identify these cases, as
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Mitogen logs all strings it receives during connection, and how it
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interprets them.
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.. _mitogen-get-stack:
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The `mitogen_get_stack` Action
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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When a Mitogen strategy is loaded, a special ``mitogen_get_stack`` action is
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available that returns a concise description of the connection configuration as
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extracted from Ansible and passed to the core library. Using it, you can learn
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whether a problem lies in the Ansible extension or deeper in library code.
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The action may be used in a playbook as ``mitogen_get_stack:`` just like a
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regular module, or directly from the command-line::
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$ ANSIBLE_STRATEGY=mitogen_linear ansible -m mitogen_get_stack -b -k k3
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SSH password:
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k3 | SUCCESS => {
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"changed": true,
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"result": [
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{
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"kwargs": {
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"check_host_keys": "enforce",
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"connect_timeout": 10,
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"hostname": "k3",
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"identities_only": false,
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"identity_file": null,
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"password": "mysecretpassword",
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"port": null,
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"python_path": null,
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"ssh_args": [
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"-C",
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"-o",
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"ControlMaster=auto",
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"-o",
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"ControlPersist=60s"
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],
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"ssh_debug_level": null,
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"ssh_path": "ssh",
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"username": null
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},
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"method": "ssh"
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},
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{
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"enable_lru": true,
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"kwargs": {
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"connect_timeout": 10,
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"password": null,
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"python_path": null,
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"sudo_args": [
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"-H",
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"-S",
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"-n"
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],
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"sudo_path": null,
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"username": "root"
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},
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"method": "sudo"
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}
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]
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}
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Each object in the list represents a single 'hop' in the connection, from
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nearest to furthest. Unlike in Ansible, the core library treats ``become``
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steps and SSH steps identically, so they are represented distinctly in the
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output.
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The presence of ``null`` means no explicit value was extracted from Ansible,
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and either the Mitogen library or SSH will choose a value for the parameter. In
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the example above, Mitogen will choose ``/usr/bin/python`` for ``python_path``,
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and SSH will choose ``22`` for ``port``, or whatever ``Port`` it parses from
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``~/.ssh/config``. Note the presence of ``null`` may indicate the extension
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failed to extract the correct value.
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When using ``mitogen_get_stack`` to diagnose a problem, pay special attention
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to ensuring the invocation exactly matches the problematic task. For example,
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if the failing task has ``delegate_to:`` or ``become:`` enabled, the
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``mitogen_get_stack`` invocation must include those statements in order for the
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output to be accurate.
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If a playbook cannot start at all, you may need to temporarily use
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``gather_facts: no`` to allow the first task to proceed. This action does not
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create connections, so if it is the first task, it is still possible to review
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its output.
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The `mitogen_ssh_debug_level` Variable
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Mitogen has support for capturing SSH diagnostic logs, and integrating them
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into the regular debug log output produced when ``-vvv`` is active. This
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provides a single audit trail of every component active during SSH
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authentication.
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Particularly for authentication failures, setting this variable to 3, in
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combination with ``-vvv``, allows review of every parameter passed to SSH, and
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review of every action SSH attempted during authentication.
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For example, this method can be used to ascertain whether SSH attempted agent
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authentication, or what private key files it was able to access and which it tried.
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.. _diagnosing-hangs:
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Diagnosing Hangs
|
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David Wilson
5 years ago