fix: Start listening after schema cache load

This change ensures PostgREST starts listening on a server socket only after it loaded the schema cache and is ready to handle requests. It is no longer going to return 503 errors during startup until the schema cache is loaded.

CHANGELOG.md

@@ -22,6 +22,7 @@ All notable changes to this project will be documented in this file. From versio
 - Remove automatic transaction retries on `40001 (serialization_failure)` errors to prevent replication lag by @laurenceisla in #3673
 - Fix unexpected results when embedding and filtering the same table more than once by @laurenceisla in #4075
 - If the schema cache fails to reload, PostgREST will no longer stop serving requests and will continue doing so in a "best effort" basis by @mkleczek in #4873 #4869
+- Stop reporting 503s errors unnecessarily while the schema cache is loading at startup by @mkleczek in #4880
 
 ### Changed
 

src/PostgREST/Admin.hs

@@ -22,20 +22,20 @@ import qualified PostgREST.AppState as AppState
 import qualified Network.Socket as NS
 import           Protolude
 
-runAdmin :: AppState -> Maybe NS.Socket -> NS.Socket -> Warp.Settings -> IO ()
+runAdmin :: AppState -> Maybe NS.Socket -> IO (Maybe NS.Socket) -> Warp.Settings -> IO ()
-runAdmin appState maybeAdminSocket socketREST settings = do
+runAdmin appState maybeAdminSocket getSocketREST settings = do
   whenJust maybeAdminSocket $ \adminSocket -> do
     address <- resolveSocketToAddress adminSocket
     observer $ AdminStartObs address
     void . forkIO $ Warp.runSettingsSocket settings adminSocket adminApp
   where
-    adminApp = admin appState socketREST
+    adminApp = admin appState getSocketREST
     observer = AppState.getObserver appState
 
 -- | PostgREST admin application
-admin :: AppState.AppState -> NS.Socket -> Wai.Application
+admin :: AppState.AppState -> IO (Maybe NS.Socket) -> Wai.Application
-admin appState socketREST req respond  = do
+admin appState getSocketREST req respond = do
-  isMainAppReachable  <- isRight <$> reachMainApp socketREST
+  isMainAppReachable <- getSocketREST >>= maybe (pure False) (fmap isRight . reachMainApp)
   isLoaded <- AppState.isLoaded appState
   isPending <- AppState.isPending appState
 
@@ -44,8 +44,8 @@ admin appState socketREST req respond  = do
       respond $ Wai.responseLBS (if isMainAppReachable then HTTP.status200 else HTTP.status500) [] mempty
     ["ready"] ->
       let
-        status | not isMainAppReachable = HTTP.status500
+        status | isPending              = HTTP.status503
-               | isPending              = HTTP.status503
+               | not isMainAppReachable = HTTP.status500
                | isLoaded               = HTTP.status200
                | otherwise              = HTTP.status500
       in

src/PostgREST/App.hs

@@ -26,7 +26,9 @@ import System.IO.Error  (ioeGetErrorType)
 import Control.Monad.Except     (liftEither)
 import Control.Monad.Extra      (whenJust)
 import Data.Either.Combinators  (mapLeft, whenLeft)
-import Data.String              (IsString (..))
+import Data.IORef               (atomicWriteIORef, newIORef,
+                                 readIORef)
+import Data.String              (IsString (..), String)
 import Network.Wai.Handler.Warp (defaultSettings, setHost,
                                  setOnException, setPort,
                                  setServerName)
@@ -71,28 +73,38 @@ import qualified Network.HTTP.Types        as HTTP
 import           Network.HTTP.Types.Header (hVary)
 import qualified Network.Socket            as NS
 import           PostgREST.Unix            (createAndBindDomainSocket)
-import           Protolude                 hiding (Handler)
+import           System.Posix.Types        (FileMode)
+
+import Protolude hiding (Handler)
 
 run :: AppState -> IO ()
 run appState = do
   conf <- AppState.getConfig appState
 
-  AppState.schemaCacheLoader appState -- Loads the initial SchemaCache
+  mainSocketRef <- newIORef Nothing
-  (mainSocket, adminSocket) <- initSockets conf
+  adminSocket <- initAdminServerSocket conf
+
   let closeSockets = do
         whenJust adminSocket NS.close
-        NS.close mainSocket
+        readIORef mainSocketRef >>= foldMap NS.close
   Unix.installSignalHandlers observer closeSockets (AppState.schemaCacheLoader appState) (AppState.readInDbConfig False appState)
 
+  Admin.runAdmin appState adminSocket (readIORef mainSocketRef) (serverSettings conf)
+
   Listener.runListener appState
 
-  Admin.runAdmin appState adminSocket mainSocket (serverSettings conf)
+  -- Kick off and wait for the initial SchemaCache load before creating the
+  -- main API socket.
+  AppState.schemaCacheLoader appState
+  AppState.waitForSchemaCacheInit appState
+
+  mainSocket <- initServerSocket conf
+  atomicWriteIORef mainSocketRef $ Just mainSocket
 
   let app = postgrest appState (AppState.schemaCacheLoader appState)
 
-  do
+  address <- resolveSocketToAddress mainSocket
-    address <- resolveSocketToAddress mainSocket
+  observer $ AppServerAddressObs address
-    observer $ AppServerAddressObs address
 
   Warp.runSettingsSocket (serverSettings conf & setOnException onWarpException) mainSocket app
   where
@@ -255,24 +267,23 @@ addRetryHint delay response = do
 isServiceUnavailable :: Wai.Response -> Bool
 isServiceUnavailable response = Wai.responseStatus response == HTTP.status503
 
-type AppSockets = (NS.Socket, Maybe NS.Socket)
+initSocket :: (Applicative f, Traversable f) => Maybe String -> FileMode -> Text -> f Int -> IO (f NS.Socket)
-
+initSocket unixSocket unixSocketMode tcpHost tcpPort =
-initSockets :: AppConfig -> IO AppSockets
+  maybe initTCPSocket initDomainSocket unixSocket
-initSockets AppConfig{..} = do
+  where
-  sock <- case configServerUnixSocket of
+    initTCPSocket = traverse (`bindPortTCP` (fromString $ T.unpack tcpHost)) tcpPort
     -- I'm not using `streaming-commons`' bindPath function here because it's not defined for Windows,
     -- but we need to have runtime error if we try to use it in Windows, not compile time error
-    Just path -> createAndBindDomainSocket path configServerUnixSocketMode
+    initDomainSocket = fmap pure . (`createAndBindDomainSocket` unixSocketMode)
-    Nothing -> bindPortTCP configServerPort (fromString $ T.unpack configServerHost)
 
-  adminSock <- case configAdminServerUnixSocket of
+initServerSocket :: AppConfig -> IO NS.Socket
-    Just path -> do
+initServerSocket AppConfig{..} =
-      adminSock <- createAndBindDomainSocket path configAdminServerUnixSocketMode
+  runIdentity <$> initSocket
-      pure $ Just adminSock
+    configServerUnixSocket configServerUnixSocketMode
-    Nothing -> case configAdminServerPort of
+    configServerHost (pure configServerPort)
-      Just adminPort -> do
-        adminSock <- bindPortTCP adminPort (fromString $ T.unpack configAdminServerHost)
-        pure $ Just adminSock
-      Nothing -> pure Nothing
 
-  pure (sock, adminSock)
+initAdminServerSocket :: AppConfig -> IO (Maybe NS.Socket)
+initAdminServerSocket AppConfig{..} =
+  initSocket
+    configAdminServerUnixSocket configAdminServerUnixSocketMode
+    configAdminServerHost configAdminServerPort

src/PostgREST/AppState.hs

@@ -25,6 +25,7 @@ module PostgREST.AppState
   , getObserver
   , isLoaded
   , isPending
+  , waitForSchemaCacheInit
   ) where
 
 import qualified Data.ByteString.Char8      as BS
@@ -51,6 +52,9 @@ import Data.IORef         (IORef, atomicWriteIORef, newIORef,
                            readIORef)
 import Data.Time.Clock    (UTCTime, getCurrentTime)
 
+import Control.Concurrent.STM            (TMVar, newEmptyTMVarIO,
+                                          putTMVar, readTMVar,
+                                          tryReadTMVar, tryTakeTMVar)
 import PostgREST.Auth.JwtCache           (JwtCacheState, update)
 import PostgREST.Config                  (AppConfig (..),
                                           readAppConfig,
@@ -98,9 +102,11 @@ data AppState = AppState
   }
 
 -- | Schema cache status.
--- Empty means pending and full means loaded.
+-- Empty means initial loading on startup, False means pending and True means loaded.
+-- "Initial" state is needed so that we can wait with application socket listening
+-- until after initial schema cache querying.
 newtype SchemaCacheStatus = SchemaCacheStatus
-  { getSCStatusMVar :: MVar ()
+  { getSCStatusTMVar :: TMVar Bool
   }
 
 init :: AppConfig -> IO AppState
@@ -368,16 +374,21 @@ retryingSchemaCacheLoad appState@AppState{stateObserver=observer, stateMainThrea
     oneSecondInUs = 1000000 -- one second in microseconds
 
 newSchemaCacheStatus :: IO SchemaCacheStatus
-newSchemaCacheStatus = SchemaCacheStatus <$> newEmptyMVar
+newSchemaCacheStatus = SchemaCacheStatus <$> newEmptyTMVarIO
 
 markSchemaCachePending :: AppState -> IO ()
-markSchemaCachePending = void . tryTakeMVar . getSCStatusMVar . stateSCacheStatus
+markSchemaCachePending = atomically . liftA2 (*>) tryTakeTMVar (`putTMVar` False) . getSCStatusTMVar . stateSCacheStatus
 
 markSchemaCacheLoaded :: AppState -> IO ()
-markSchemaCacheLoaded = void . (`tryPutMVar` ()) . getSCStatusMVar . stateSCacheStatus
+markSchemaCacheLoaded = atomically . liftA2 (*>) tryTakeTMVar (`putTMVar` True) . getSCStatusTMVar . stateSCacheStatus
 
 isSchemaCacheLoaded :: AppState -> IO Bool
-isSchemaCacheLoaded = fmap not . isEmptyMVar . getSCStatusMVar . stateSCacheStatus
+isSchemaCacheLoaded = atomically . (pure . fromMaybe False <=< tryReadTMVar) . getSCStatusTMVar . stateSCacheStatus
+
+-- | Wait for initial schema cache load to either finish or retry
+-- | We wait until scStatusTMVar is not empty.
+waitForSchemaCacheInit :: AppState -> IO ()
+waitForSchemaCacheInit = atomically . void . readTMVar . getSCStatusTMVar . stateSCacheStatus
 
 -- | Reads the in-db config and reads the config file again
 -- | We don't retry reading the in-db config after it fails immediately, because it could have user errors. We just report the error and continue.

src/PostgREST/Config.hs

@@ -128,7 +128,8 @@ data AppConfig = AppConfig
   , configAdminServerUnixSocketMode :: FileMode
   , configRoleSettings              :: RoleSettings
   , configRoleIsoLvl                :: RoleIsolationLvl
-  , configInternalSCQuerySleep      :: Maybe Int32
+  , configInternalSCQuerySleepFst   :: Maybe Int32
+  , configInternalSCQuerySleepSnd   :: Maybe Int32
   }
 
 data LogLevel = LogCrit | LogError | LogWarn | LogInfo | LogDebug
@@ -332,6 +333,7 @@ parser optPath env dbSettings roleSettings roleIsolationLvl =
     <*> parseSocketFileMode "admin-server-unix-socket-mode"
     <*> pure roleSettings
     <*> pure roleIsolationLvl
+    <*> optInt "internal-schema-cache-query-sleep-before-queries"
     <*> optInt "internal-schema-cache-query-sleep"
   where
     parseErrorVerbosity :: C.Key -> C.Parser C.Config Verbosity

src/PostgREST/SchemaCache.hs

@@ -156,6 +156,9 @@ maxDbTablesForFuzzySearch = 500
 querySchemaCache :: AppConfig -> SQL.Transaction (SchemaCache, Maybe QueryTimings)
 querySchemaCache conf@AppConfig{..} = do
   SQL.sql "set local schema ''" -- This voids the search path. The following queries need this for getting the fully qualified name(schema.name) of every db object
+
+  for_ configInternalSCQuerySleepFst (`SQL.statement` sleepCall) -- only used for testing
+
   tabs    <- sqlTimedStmt gucTbls  conf   allTables
   keyDeps <- sqlTimedStmt gucKDeps conf   allViewsKeyDependencies
   m2oRels <- sqlTimedStmt gucRels  mempty allM2OandO2ORels
@@ -166,9 +169,8 @@ querySchemaCache conf@AppConfig{..} = do
   tzones  <- if configDbTimezoneEnabled
     then sqlTimedStmt gucTzones mempty timezones
     else pure S.empty
-  _       <-
+
-    let sleepCall = SQL.Statement "select pg_sleep($1 / 1000.0)" (param HE.int4) HD.noResult True in
+  for_ configInternalSCQuerySleepSnd (`SQL.statement` sleepCall) -- only used for testing
-    for_ configInternalSCQuerySleep (`SQL.statement` sleepCall) -- only used for testing
 
   qsTime <-
     if isLogDebug
@@ -195,6 +197,7 @@ querySchemaCache conf@AppConfig{..} = do
     schemas = toList configDbSchemas
     isLogDebug = configLogLevel == LogDebug
     sqlTimedStmt = sqlTimedStatement isLogDebug
+    sleepCall = SQL.Statement "select pg_sleep($1 / 1000.0)" (param HE.int4) HD.noResult True
 
 -- | overrides detected relationships with the computed relationships and gets the RelationshipsMap
 getOverrideRelationshipsMap :: [Relationship] -> [Relationship] -> RelationshipsMap

test/io/test_io.py

@@ -6,6 +6,7 @@ import signal
 import subprocess
 import time
 import pytest
+import requests
 
 from config import CONFIGSDIR, FIXTURES, SECRET
 from util import (
@@ -1090,7 +1091,7 @@ def test_empty_schema_cache_log_contains_jwt_role(defaultenv):
 
     env = {
         **defaultenv,
-        "PGRST_INTERNAL_SCHEMA_CACHE_QUERY_SLEEP": "1000",
+        "PGRST_DB_SCHEMAS": "non_existent_schema_aaaa",
         "PGRST_JWT_SECRET": SECRET,
     }
     headers = jwtauthheader({"role": "postgrest_test_author"}, SECRET)
@@ -1543,14 +1544,19 @@ def test_log_postgrest_host_and_port(host, defaultenv):
     with run(
         env=defaultenv, host=host, port=port, no_startup_stdout=False
     ) as postgrest:
-        output = postgrest.read_stdout(nlines=10)
+        output = postgrest.read_stdout(nlines=11)
 
+        # Cannot assume a particular log entry order
+        # Listening on a socket happens after schema querying
+        # but is concurrent to the schema loading process
+        # and migh happen before or after writing of the
+        # "Schema cache loaded" log entry
         if is_unix:
-            re.match(r'API server listening on "/tmp/.*\.sock"', output[2])
+            match_log(output, [r".*API server listening on .*/tmp/.*\.sock"])
         elif is_ipv6(host):
-            assert f"API server listening on [{host}]:{port}" in output[2]
+            match_log(output, [r".*API server listening on \[.+]:\d+"])
         else:  # IPv4
-            assert f"API server listening on {host}:{port}" in output[2]
+            match_log(output, [r".*API server listening on .+:\d+"])
 
 
 def test_succeed_w_role_having_superuser_settings(defaultenv):
@@ -1818,17 +1824,24 @@ def test_pgrst_log_503_client_error_to_stderr(defaultenv):
         assert any(log_message in line for line in output)
 
 
-def test_log_error_when_empty_schema_cache_on_startup_to_stderr(defaultenv):
+def test_log_error_when_schema_cache_load_error_on_startup_to_stderr(defaultenv):
-    "Should log the 503 error message when there is an empty schema cache on startup"
+    "Should log the 503 error message when there is an error loading schema cache on startup"
 
     env = {
         **defaultenv,
-        "PGRST_INTERNAL_SCHEMA_CACHE_QUERY_SLEEP": "300",
+        "PGRST_INTERNAL_SCHEMA_CACHE_QUERY_SLEEP_BEFORE_QUERIES": "1000",
+        "PGRST_DB_SCHEMAS": "non_existent_schema_aaaa",
     }
 
     with run(env=env, wait_for=None) as postgrest:
         postgrest.wait_until_scache_starts_loading()
 
+        # First call should fail with connection refused
+        with pytest.raises(requests.ConnectionError):
+            postgrest.session.get("/projects")
+
+        # Next call should return 503
+        time.sleep(1)
         response = postgrest.session.get("/projects")
         assert response.status_code == 503
 
@@ -1840,7 +1853,7 @@ def test_log_error_when_empty_schema_cache_on_startup_to_stderr(defaultenv):
 
 
 def test_no_double_schema_cache_reload_on_empty_schema(defaultenv):
-    "Should only load the schema cache once on a 503 error when there's an empty schema cache on startup"
+    "Should only load the schema cache once when there's an empty schema cache on startup"
 
     env = {
         **defaultenv,
@@ -1850,12 +1863,15 @@ def test_no_double_schema_cache_reload_on_empty_schema(defaultenv):
     with run(env=env, wait_for=None) as postgrest:
         postgrest.wait_until_scache_starts_loading()
 
-        response = postgrest.session.get("/projects")
+        with pytest.raises(requests.ConnectionError):
-        assert response.status_code == 503
+            postgrest.session.get("/projects")
 
         # Should wait enough time to load the schema cache twice to guarantee that the test is valid
         time.sleep(1)
 
+        response = postgrest.session.get("/projects")
+        assert response.status_code == 200
+
         response = postgrest.admin.get("/metrics")
         assert response.status_code == 200
         assert 'pgrst_schema_cache_loads_total{status="SUCCESS"} 1.0' in response.text
@@ -1937,7 +1953,7 @@ def test_schema_cache_error_observation(defaultenv):
         output = postgrest.read_stdout(nlines=9)
         assert (
             "Failed to load the schema cache using db-schemas=public and db-extra-search-path=x"
-            in output[7]
+            in output[6]
         )
 
 

test/observability/ObsHelper.hs

@@ -119,7 +119,8 @@ baseCfg = let secret = encodeUtf8 "reallyreallyreallyreallyverysafe" in
   , configAdminServerUnixSocketMode = 432
   , configRoleSettings              = mempty
   , configRoleIsoLvl                = mempty
-  , configInternalSCQuerySleep      = Nothing
+  , configInternalSCQuerySleepFst   = Nothing
+  , configInternalSCQuerySleepSnd   = Nothing
   , configServerTimingEnabled       = True
   }
 

test/spec/SpecHelper.hs

@@ -160,7 +160,8 @@ baseCfg = let secret = encodeUtf8 "reallyreallyreallyreallyverysafe" in
   , configAdminServerUnixSocketMode = 432
   , configRoleSettings              = mempty
   , configRoleIsoLvl                = mempty
-  , configInternalSCQuerySleep      = Nothing
+  , configInternalSCQuerySleepFst   = Nothing
+  , configInternalSCQuerySleepSnd   = Nothing
   , configServerTimingEnabled       = True
   }