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