Added mongodb admin commands to add and remove members from the

replicaset

bigchaindb/backend/admin.py

@@ -20,3 +20,13 @@ def set_shards(connection, *, shards):
 @singledispatch
 def set_replicas(connection, *, replicas):
     raise NotImplementedError
+
+
+@singledispatch
+def add_replicas(connection, *, replicas):
+    raise NotImplementedError
+
+
+@singledispatch
+def remove_replicas(connection, *, replicas):
+    raise NotImplementedError

bigchaindb/backend/mongodb/admin.py

@@ -0,0 +1,59 @@
+"""Database configuration functions."""
+import logging
+
+from bigchaindb.backend import admin
+from bigchaindb.backend.utils import module_dispatch_registrar
+from bigchaindb.backend.mongodb.connection import MongoDBConnection
+
+logger = logging.getLogger(__name__)
+
+register_admin = module_dispatch_registrar(admin)
+
+
+@register_admin(MongoDBConnection)
+def add_replicas(connection, replicas):
+    """Add a set of replicas to the replicaset
+
+    Args:
+        replicas list of strings: of the form "hostname:port".
+    """
+    # get current configuration
+    conf = connection.conn.admin.command('replSetGetConfig')
+
+    # MongoDB does not automatically add and id for the members so we need
+    # to chose one that does not exists yet. The safest way is to use
+    # incrementing ids, so we first check what is the highest id already in
+    # the set and continue from there.
+    cur_id = max([member['_id'] for member in conf['config']['members']])
+
+    # add the nodes to the members list of the replica set
+    for replica in replicas:
+        cur_id += 1
+        conf['config']['members'].append({'_id': cur_id, 'host': replica})
+
+    # increase the configuration version number
+    conf['config']['version'] += 1
+
+    # apply new configuration
+    return connection.conn.admin.command('replSetReconfig', conf['config'])
+
+
+@register_admin(MongoDBConnection)
+def remove_replicas(connection, replicas):
+    """Remove a set of replicas from the replicaset
+
+    """
+    # get the current configuration
+    conf = connection.conn.admin.command('replSetGetConfig')
+
+    # remove the nodes from the members list in the replica set
+    conf['config']['members'] = list(
+        filter(lambda member: member['host'] not in replicas,
+               conf['config']['members'])
+    )
+
+    # increase the configuration version number
+    conf['config']['version'] += 1
+
+    # apply new configuration
+    return connection.conn.admin.command('replSetReconfig', conf['config'])