Dustin C. Hatch
b9a046c7f4
One major weakness with Ansible's "lookup" plugins is that they are evaluated _every single time they are used_, even indirectly. This means, for example, a shell command could be run many times, potentially resulting in different values, or executing a complex calculation that always provides the same result. Ansible does not have a built-in way to cache the result of a `lookup` or `query` call, so I created this one. It's inspired by [ansible-cached-lookup][0], which didn't actually work and is apparently unmaintained. Instead of using a hard-coded file-based caching system, however, my plugin uses Ansible's configuration and plugin infrastructure to store values with any available cache plugin. Although looking up the _pyrocufflink.net_ wildcard certificate with the Kubernetes API isn't particularly expensive by itself right now, I can envision several other uses that may be. Having this plugin available could speed up future playbooks. [0]: https://pypi.org/project/ansible-cached-lookup
104 lines
2.9 KiB
Python
104 lines
2.9 KiB
Python
import functools
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import hashlib
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from ansible.constants import config
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from ansible.errors import AnsibleError
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from ansible.plugins.loader import cache_loader, lookup_loader
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from ansible.plugins.lookup import LookupBase, display
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DOCUMENTATION = """
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lookup: cache
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author: Dustin C. Hatch <dustin@hatch.name>
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options:
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cache_plugin:
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description:
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- Cache plugin to use
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type: str
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required: false
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default: memory
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env:
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- name: ANSIBLE_LOOKUP_CACHE_PLUGIN
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ini:
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- section: lookup
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key: cache_plugin
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cache_timeout:
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description:
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- Cache duration in seconds
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default: 3600
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type: int
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env:
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- name: ANSIBLE_LOOKUP_CACHE_TIMEOUT
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ini:
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- section: lookup
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key: cache_timeout
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cache_connection:
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description:
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- Cache connection data or path, read cache plugin documentation for specifics.
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type: str
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env:
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- name: ANSIBLE_LOOKUP_CACHE_CONNECTION
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ini:
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- section: lookup
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key: cache_connection
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cache_prefix:
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description:
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- Prefix to use for cache plugin files/tables
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default: ''
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env:
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- name: ANSIBLE_LOOKUP_CACHE_PREFIX
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ini:
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- section: lookup
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key: cache_prefix
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"""
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def _get_option(key: str):
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return config.get_config_value(
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key, plugin_type='lookup', plugin_name='cache'
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)
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@functools.cache
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def _get_cache():
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cache_plugin = _get_option('cache_plugin')
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cache_options = {}
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if cache_connection := _get_option('cache_connection'):
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cache_options['_uri'] = cache_connection
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if cache_timeout := _get_option('cache_timeout'):
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cache_options['_timeout'] = cache_timeout
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if cache_prefix := _get_option('cache_prefix'):
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cache_options['_prefix'] = cache_prefix
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return cache_loader.get(cache_plugin, **cache_options)
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class LookupModule(LookupBase):
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def run(self, terms, variables=None, **kwargs):
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cache = _get_cache()
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display.v(f'lookup cache: using cache plugin {cache.plugin_name}')
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h = hashlib.sha1()
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h.update(str((terms, kwargs)).encode('utf-8'))
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key = h.hexdigest()
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try:
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result = cache.get(key)
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except KeyError:
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result = None
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if result is None:
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lookup_name, terms = terms[0], terms[1:]
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lookup = lookup_loader.get(
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lookup_name, loader=self._loader, templar=self._templar
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)
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if lookup is None:
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raise AnsibleError(
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f'Could not find lookup plugin {lookup_name!r}'
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)
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result = lookup.run(terms, variables=variables, **kwargs)
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cache.set(key, result)
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else:
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str_terms = ', '.join(repr(t) for t in terms)
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str_kwargs = ', '.join(f'{k}={v!r}' for k, v in kwargs.items())
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display.v(
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'lookup cache: found cached value for'
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f' lookup({str_terms}, {str_kwargs})'
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)
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return result
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