Sync charm-helpers.

hooks/charmhelpers/contrib/peerstorage/__init__.py

@@ -0,0 +1,83 @@
+from charmhelpers.core.hookenv import (
+    relation_ids,
+    relation_get,
+    local_unit,
+    relation_set,
+)
+
+"""
+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, so this is really useful for
+services that issue usernames/passwords to remote services.
+
+def shared_db_changed()
+    # Only the lead unit should create passwords
+    if not is_leader():
+        return
+    username = relation_get('username')
+    key = '{}.password'.format(username)
+    # Attempt to retrieve any existing password for this user
+    password = peer_retrieve(key)
+    if password is None:
+        # New user, create password and store
+        password = pwgen(length=64)
+        peer_store(key, password)
+    create_access(username, password)
+    relation_set(password=password)
+
+
+def cluster_changed()
+    # Echo any relation data other that *-address
+    # back onto the peer relation so all units have
+    # all *.password keys stored on their local relation
+    # for later retrieval.
+    peer_echo()
+
+"""
+
+
+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_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):
+    """Echo filtered attributes back onto the same relation for storage
+
+    Note that this helper must only be called within a peer relation
+    changed hook
+    """
+    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 rdata.iteritems():
+            for include in includes:
+                if include in attribute:
+                    echo_data[attribute] = value
+    if len(echo_data) > 0:
+        relation_set(relation_settings=echo_data)