Add /read-only-sync endpoint (#2305) (#2311)

`/read-only-sync` mirrors `/read-only`, but only returns `200` on a replica if this replica is a synchronous standby.

docs/rest_api.rst

@@ -44,8 +44,11 @@ For all health check ``GET`` requests Patroni returns a JSON document with the s
 
 - ``GET /synchronous`` or ``GET /sync``: returns HTTP status code **200** only when the Patroni node is running as a synchronous standby.
 
+- ``GET /read-only-sync``: like the above endpoint, but also includes the primary.
+
 - ``GET /asynchronous`` or ``GET /async``: returns HTTP status code **200** only when the Patroni node is running as an asynchronous standby.
 
+
 - ``GET /asynchronous?lag=<max-lag>`` or ``GET /async?lag=<max-lag>``: asynchronous standby check endpoint. In addition to checks from ``asynchronous`` or ``async``, it also checks replication latency and returns status code **200** only when it is below specified value. The key cluster.last_leader_operation from DCS is used for Leader wal position and compute latency on replica for performance reasons. max-lag can be specified in bytes (integer) or in human readable values, for e.g. 16kB, 64MB, 1GB.
 
   - ``GET /async?lag=1048576``

patroni/api.py

@@ -152,6 +152,11 @@ class RestApiHandler(BaseHTTPRequestHandler):
                 status_code = replica_status_code
             elif path in ('/async', '/asynchronous') and not is_synchronous:
                 status_code = replica_status_code
+            elif path in ('/read-only-sync', '/read-only-synchronous'):
+                if 200 in (primary_status_code, standby_leader_status_code):
+                    status_code = 200
+                elif is_synchronous:
+                    status_code = replica_status_code
 
         # check for user defined tags in query params
         if not ignore_tags and status_code == 200:

tests/test_api.py

@@ -169,6 +169,7 @@ class TestRestApiHandler(unittest.TestCase):
         MockRestApiServer(RestApiHandler, 'GET /replica?lag=10MB')
         MockRestApiServer(RestApiHandler, 'GET /replica?lag=10485760')
         MockRestApiServer(RestApiHandler, 'GET /read-only')
+        MockRestApiServer(RestApiHandler, 'GET /read-only-sync')
         with patch.object(RestApiHandler, 'get_postgresql_status', Mock(return_value={})):
             MockRestApiServer(RestApiHandler, 'GET /replica')
         with patch.object(RestApiHandler, 'get_postgresql_status', Mock(return_value={'role': 'master'})):
@@ -180,6 +181,8 @@ class TestRestApiHandler(unittest.TestCase):
         MockPatroni.dcs.cluster.is_synchronous_mode = Mock(return_value=True)
         with patch.object(RestApiHandler, 'get_postgresql_status', Mock(return_value={'role': 'replica'})):
             MockRestApiServer(RestApiHandler, 'GET /synchronous')
+        with patch.object(RestApiHandler, 'get_postgresql_status', Mock(return_value={'role': 'replica'})):
+            MockRestApiServer(RestApiHandler, 'GET /read-only-sync')
         with patch.object(RestApiHandler, 'get_postgresql_status', Mock(return_value={'role': 'replica'})):
             MockPatroni.dcs.cluster.sync.members = []
             MockRestApiServer(RestApiHandler, 'GET /asynchronous')