ade5bfa302
By default, Ansible injects a variable for every fact, prefixed with ansible_. This can result in a large number of variables for each host, which at scale can incur a performance penalty. Ansible provides a configuration option [0] that can be set to False to prevent this injection of facts. In this case, facts should be referenced via ansible_facts.<fact>. This change updates all references to Ansible facts within Kolla Ansible from using individual fact variables to using the items in the ansible_facts dictionary. This allows users to disable fact variable injection in their Ansible configuration, which may provide some performance improvement. This change disables fact variable injection in the ansible configuration used in CI, to catch any attempts to use the injected variables. [0] https://docs.ansible.com/ansible/latest/reference_appendices/config.html#inject-facts-as-vars Change-Id: I7e9d5c9b8b9164d4aee3abb4e37c8f28d98ff5d1 Partially-Implements: blueprint performance-improvements
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==============
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Ansible tuning
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==============
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In this section we cover some options for tuning Ansible for performance and
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scale.
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SSH pipelining
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--------------
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SSH pipelining is disabled in Ansible by default, but is generally safe to
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enable, and provides a reasonable performance improvement.
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.. code-block:: ini
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:caption: ``ansible.cfg``
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[ssh_connection]
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pipelining = True
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Forks
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-----
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By default Ansible executes tasks using a fairly conservative 5 process forks.
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This limits the parallelism that allows Ansible to scale. Most Ansible control
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hosts will be able to handle far more forks than this. You will need to
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experiment to find out the CPU, memory and IO limits of your machine.
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For example, to increase the number of forks to 20:
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.. code-block:: ini
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:caption: ``ansible.cfg``
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[defaults]
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forks = 20
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Fact caching
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------------
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By default, Ansible gathers facts for each host at the beginning of every play,
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unless ``gather_facts`` is set to ``false``. With a large number of hosts this
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can result in a significant amount of time spent gathering facts.
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One way to improve this is through Ansible's support for `fact caching
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<https://docs.ansible.com/ansible/latest/user_guide/playbooks_variables.html#caching-facts>`__.
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In order to make this work with Kolla Ansible, it is necessary to change
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Ansible's `gathering
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<https://docs.ansible.com/ansible/latest/reference_appendices/config.html#default-gathering>`__
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configuration option to ``smart``.
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Example
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~~~~~~~
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In the following example we configure Kolla Ansible to use fact caching using
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the `jsonfile cache plugin
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<https://docs.ansible.com/ansible/latest/plugins/cache/jsonfile.html>`__.
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.. code-block:: ini
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:caption: ``ansible.cfg``
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[defaults]
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gathering = smart
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fact_caching = jsonfile
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fact_caching_connection = /tmp/ansible-facts
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You may also wish to set the expiration timeout for the cache via ``[defaults]
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fact_caching_timeout``.
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Fact variable injection
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-----------------------
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By default, Ansible injects a variable for every fact, prefixed with
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``ansible_``. This can result in a large number of variables for each host,
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which at scale can incur a performance penalty. Ansible provides a
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`configuration option
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<https://docs.ansible.com/ansible/latest/reference_appendices/config.html#inject-facts-as-vars>`__
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that can be set to ``False`` to prevent this injection of facts. In this case,
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facts should be referenced via ``ansible_facts.<fact>``. In recent releases of
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Kolla Ansible, facts are referenced via ``ansible_facts``, allowing users to
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disable fact variable injection.
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.. code-block:: ini
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:caption: ``ansible.cfg``
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[defaults]
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inject_facts_as_vars = False
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