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Viewing changes to hooks/charmhelpers/contrib/peerstorage/__init__.py

  • Committer: james.page at ubuntu
  • Date: 2015-06-09 09:59:06 UTC
  • mfrom: (143.1.18 nova-cloud-controller)
  • Revision ID: james.page@ubuntu.com-20150609095906-o300u1j0rtk92aem
Add support for leader-election

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hooks/charmhelpers/contrib/peerstorage/__init__.py
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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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import json
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import six
 
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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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    is_relation_made,
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    relation_ids,
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    relation_get,
 
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    relation_get as _relation_get,
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    local_unit,
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    relation_set,
 
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    relation_set as _relation_set,
 
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    leader_get as _leader_get,
 
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    leader_set,
 
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    is_leader,
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)
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"""
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def leader_get(attribute=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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    """
 
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    migration_key = '__leader_get_migrated_settings__'
 
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    if not is_leader():
 
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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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    else:
 
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        migrated = set([])
 
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    try:
 
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        if migration_key in leader_settings:
 
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            del leader_settings[migration_key]
 
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    except TypeError:
 
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        pass
 
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    if attribute:
 
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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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            if peer_setting:
 
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                leader_set(settings={attribute: peer_setting})
 
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                leader_settings = peer_setting
 
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        if leader_settings:
 
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            settings_migrated = True
 
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            migrated.add(attribute)
 
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    else:
 
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        r_settings = relation_get(unit=local_unit())
 
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        if r_settings:
 
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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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                migrated.add(key)
 
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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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    """
 
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    try:
 
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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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        else:
 
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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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    """
 
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    try:
 
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        if rid in relation_ids('cluster'):
 
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            return leader_get(attribute)
 
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        else:
 
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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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    exc_list = exc_list if exc_list else []
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    peerdb_settings = peer_retrieve('-', relation_name=relation_name)
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    matched = {}
 
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    if peerdb_settings is None:
 
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        return matched
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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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                         'peer relation {}'.format(relation_name))
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def peer_echo(includes=None):
 
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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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    """
 
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    try:
 
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        is_leader()
 
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    except NotImplementedError:
 
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        pass
 
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    else:
 
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        if not force:
 
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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 = {}
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    if includes is None: