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# Copyright 2014-2015 Canonical Limited.
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# This file is part of charm-helpers.
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# charm-helpers is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Lesser General Public License version 3 as
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# published by the Free Software Foundation.
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# charm-helpers is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Lesser General Public License for more details.
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# You should have received a copy of the GNU Lesser General Public License
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# along with charm-helpers. If not, see <http://www.gnu.org/licenses/>.
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from charmhelpers.core.hookenv import relation_id as current_relation_id
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from charmhelpers.core.hookenv import (
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relation_get as _relation_get,
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relation_set as _relation_set,
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leader_get as _leader_get,
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This helper provides functions to support use of a peer relation
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for basic key/value storage, with the added benefit that all storage
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can be replicated across peer units.
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To use this, the "peer_echo()" method has to be called form the peer
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relation's relation-changed hook:
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@hooks.hook("cluster-relation-changed") # Adapt the to your peer relation name
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def cluster_relation_changed():
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Once this is done, you can use peer storage from anywhere:
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@hooks.hook("some-hook")
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# You can store and retrieve key/values this way:
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if is_relation_made("cluster"): # from charmhelpers.core.hookenv
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# There are peers available so we can work with peer storage
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peer_store("mykey", "myvalue")
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value = peer_retrieve("mykey")
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print "No peers joind the relation, cannot share key/values :("
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def leader_get(attribute=None, rid=None):
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"""Wrapper to ensure that settings are migrated from the peer relation.
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This is to support upgrading an environment that does not support
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Juju leadership election to one that does.
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If a setting is not extant in the leader-get but is on the relation-get
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peer rel, it is migrated and marked as such so that it is not re-migrated.
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migration_key = '__leader_get_migrated_settings__'
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return _leader_get(attribute=attribute)
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settings_migrated = False
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leader_settings = _leader_get(attribute=attribute)
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previously_migrated = _leader_get(attribute=migration_key)
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if previously_migrated:
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migrated = set(json.loads(previously_migrated))
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if migration_key in leader_settings:
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del leader_settings[migration_key]
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if attribute in migrated:
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return leader_settings
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# If attribute not present in leader db, check if this unit has set
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# the attribute in the peer relation
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if not leader_settings:
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peer_setting = _relation_get(attribute=attribute, unit=local_unit(),
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leader_set(settings={attribute: peer_setting})
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leader_settings = peer_setting
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settings_migrated = True
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migrated.add(attribute)
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r_settings = _relation_get(unit=local_unit(), rid=rid)
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for key in set(r_settings.keys()).difference(migrated):
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# Leader setting wins
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if not leader_settings.get(key):
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leader_settings[key] = r_settings[key]
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settings_migrated = True
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if settings_migrated:
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leader_set(**leader_settings)
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if migrated and settings_migrated:
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migrated = json.dumps(list(migrated))
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leader_set(settings={migration_key: migrated})
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return leader_settings
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def relation_set(relation_id=None, relation_settings=None, **kwargs):
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"""Attempt to use leader-set if supported in the current version of Juju,
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otherwise falls back on relation-set.
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Note that we only attempt to use leader-set if the provided relation_id is
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a peer relation id or no relation id is provided (in which case we assume
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we are within the peer relation context).
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if relation_id in relation_ids('cluster'):
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return leader_set(settings=relation_settings, **kwargs)
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raise NotImplementedError
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except NotImplementedError:
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return _relation_set(relation_id=relation_id,
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relation_settings=relation_settings, **kwargs)
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def relation_get(attribute=None, unit=None, rid=None):
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"""Attempt to use leader-get if supported in the current version of Juju,
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otherwise falls back on relation-get.
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Note that we only attempt to use leader-get if the provided rid is a peer
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relation id or no relation id is provided (in which case we assume we are
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within the peer relation context).
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if rid in relation_ids('cluster'):
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return leader_get(attribute, rid)
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raise NotImplementedError
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except NotImplementedError:
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return _relation_get(attribute=attribute, rid=rid, unit=unit)
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def peer_retrieve(key, relation_name='cluster'):
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"""Retrieve a named key from peer relation `relation_name`."""
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cluster_rels = relation_ids(relation_name)
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if len(cluster_rels) > 0:
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cluster_rid = cluster_rels[0]
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return relation_get(attribute=key, rid=cluster_rid,
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raise ValueError('Unable to detect'
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'peer relation {}'.format(relation_name))
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def peer_retrieve_by_prefix(prefix, relation_name='cluster', delimiter='_',
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inc_list=None, exc_list=None):
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""" Retrieve k/v pairs given a prefix and filter using {inc,exc}_list """
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inc_list = inc_list if inc_list else []
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exc_list = exc_list if exc_list else []
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peerdb_settings = peer_retrieve('-', relation_name=relation_name)
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if peerdb_settings is None:
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for k, v in peerdb_settings.items():
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full_prefix = prefix + delimiter
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if k.startswith(full_prefix):
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new_key = k.replace(full_prefix, '')
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if new_key in exc_list:
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if new_key in inc_list or len(inc_list) == 0:
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def peer_store(key, value, relation_name='cluster'):
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"""Store the key/value pair on the named peer relation `relation_name`."""
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cluster_rels = relation_ids(relation_name)
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if len(cluster_rels) > 0:
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cluster_rid = cluster_rels[0]
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relation_set(relation_id=cluster_rid,
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relation_settings={key: value})
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raise ValueError('Unable to detect '
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'peer relation {}'.format(relation_name))
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def peer_echo(includes=None, force=False):
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"""Echo filtered attributes back onto the same relation for storage.
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This is a requirement to use the peerstorage module - it needs to be called
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from the peer relation's changed hook.
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If Juju leader support exists this will be a noop unless force is True.
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except NotImplementedError:
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return # NOOP if leader-election is supported
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# Use original non-leader calls
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relation_get = _relation_get
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relation_set = _relation_set
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rdata = relation_get()
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echo_data = rdata.copy()
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for ex in ['private-address', 'public-address']:
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for attribute, value in six.iteritems(rdata):
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for include in includes:
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if include in attribute:
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echo_data[attribute] = value
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if len(echo_data) > 0:
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relation_set(relation_settings=echo_data)
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def peer_store_and_set(relation_id=None, peer_relation_name='cluster',
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peer_store_fatal=False, relation_settings=None,
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delimiter='_', **kwargs):
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"""Store passed-in arguments both in argument relation and in peer storage.
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It functions like doing relation_set() and peer_store() at the same time,
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@param relation_id: the id of the relation to store the data on. Defaults
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to the current relation.
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@param peer_store_fatal: Set to True, the function will raise an exception
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should the peer sotrage not be avialable."""
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relation_settings = relation_settings if relation_settings else {}
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relation_set(relation_id=relation_id,
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relation_settings=relation_settings,
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if is_relation_made(peer_relation_name):
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for key, value in six.iteritems(dict(list(kwargs.items()) +
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list(relation_settings.items()))):
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key_prefix = relation_id or current_relation_id()
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peer_store(key_prefix + delimiter + key,
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relation_name=peer_relation_name)
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raise ValueError('Unable to detect '
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'peer relation {}'.format(peer_relation_name))
added
removed
hooks/charmhelpers/contrib/peerstorage/__init__.py
