Add support for per-member tags.

Tags are labels assigned to individual members in order
to alter its default behavior, i.e. exclude from the
leader election or indicate a possibility to create base
backups from the member.

This commit only adds support for setting tags in the
configuration file, exposes the tags to DCS /member subkey
and returns the tags in a response of the API request. At
the moment the tag names are not validated, nor they are
interpreted in any way.

Support for setting tags via the API is also in the scope
of further work.

patroni/__init__.py

@@ -18,6 +18,7 @@ class Patroni:
 
     def __init__(self, config):
         self.nap_time = config['loop_wait']
+        self.tags = config.get('tags', dict())
         self.postgresql = Postgresql(config['postgresql'])
         self.dcs = self.get_dcs(self.postgresql.name, config)
         host, port = config['restapi']['listen'].split(':')

patroni/api.py

@@ -46,6 +46,7 @@ class RestApiHandler(BaseHTTPRequestHandler):
 
         path = '/master' if self.path == '/' else self.path
         response = self.get_postgresql_status()
+        response.update(self.get_tags())
 
         patroni = self.server.patroni
         cluster = patroni.dcs.cluster
@@ -75,6 +76,7 @@ class RestApiHandler(BaseHTTPRequestHandler):
 
     def do_GET_patroni(self):
         response = self.get_postgresql_status(True)
+        response.update(self.get_tags())
 
         self.send_response(200)
         self.send_header('Content-Type', 'application/json')
@@ -174,6 +176,9 @@ class RestApiHandler(BaseHTTPRequestHandler):
                 state = 'unknown' if state == 'running' else state
             return {'state': state}
 
+    def get_tags(self):
+        return {'tags': self.server.patroni.tags}
+
 
 class RestApiServer(ThreadingMixIn, HTTPServer, Thread):
 

patroni/ha.py

@@ -50,7 +50,8 @@ class Ha:
             'conn_url': self.state_handler.connection_string,
             'api_url': self.patroni.api.connection_string,
             'state': self.state_handler.state,
-            'role': self.state_handler.role
+            'role': self.state_handler.role,
+            'tags': self.patroni.tags
         }
         if data['state'] in ['running', 'restarting', 'starting']:
             try:

postgres0.yml

@@ -67,3 +67,8 @@ postgresql:
     max_replication_slots: 5
     hot_standby: "on"
     wal_log_hints: "on"
+tags:
+    nofailover: False
+    noloadbalance: False
+    clonefrom: False
+    replicatefrom: 127.0.0.1

postgres1.yml

@@ -67,3 +67,8 @@ postgresql:
     max_replication_slots: 5
     hot_standby: "on"
     wal_log_hints: "on"
+tags:
+    nofailover: False
+    noloadbalance: False
+    clonefrom: False
+    replicatefrom: 127.0.0.1

tests/test_api.py

@@ -44,6 +44,7 @@ class MockPatroni:
     postgresql = MockPostgresql()
     ha = MockHa()
     dcs = Mock()
+    tags = {}
 
 
 class MockRequest:

tests/test_ha.py

@@ -82,6 +82,7 @@ class MockPatroni:
         self.postgresql = p
         self.dcs = d
         self.api = Mock()
+        self.tags = {}
         self.api.connection_string = 'http://127.0.0.1:8008'