feat: add metric pgrst_jwt_cache_size in admin server

docs/references/observability.rst

@@ -169,6 +169,20 @@ pgrst_db_pool_max
 
 Max pool connections.
 
+JWT Cache Metric
+----------------
+
+Related to the :ref:`jwt_caching`.
+
+pgrst_jwt_cache_size
+~~~~~~~~~~~~~~~~~~~~
+
+======== =======
+**Type** Gauge
+======== =======
+
+Number of entries in JWT Cache.
+
 Traces
 ======
 

src/PostgREST/Auth.hs

@@ -44,10 +44,11 @@ import System.Clock            (TimeSpec (..))
 import System.IO.Unsafe        (unsafePerformIO)
 import System.TimeIt           (timeItT)
 
-import PostgREST.AppState (AppState, AuthResult (..), getConfig,
-                           getJwtCache, getTime)
-import PostgREST.Config   (AppConfig (..), JSPath, JSPathExp (..))
-import PostgREST.Error    (Error (..))
+import PostgREST.AppState    (AppState, AuthResult (..), getConfig,
+                              getJwtCache, getObserver, getTime)
+import PostgREST.Config      (AppConfig (..), JSPath, JSPathExp (..))
+import PostgREST.Error       (Error (..))
+import PostgREST.Observation (Observation (..))
 
 import Protolude
 
@@ -163,14 +164,22 @@ middleware appState app req respond = do
 -- | Used to retrieve and insert JWT to JWT Cache
 getJWTFromCache :: AppState -> ByteString -> Int -> IO (Either Error AuthResult) -> UTCTime -> IO (Either Error AuthResult)
 getJWTFromCache appState token maxLifetime parseJwt utc = do
-  checkCache <- C.lookup (getJwtCache appState) token
+
+  checkCache <- C.lookup jwtCache token
   authResult <- maybe parseJwt (pure . Right) checkCache
 
+
   case (authResult,checkCache) of
-    (Right res, Nothing) -> C.insert' (getJwtCache appState) (getTimeSpec res maxLifetime utc) token res
+    (Right res, Nothing) -> C.insert' jwtCache (getTimeSpec res maxLifetime utc) token res
     _                    -> pure ()
 
+  jwtCacheSize <- C.size jwtCache
+  observer $ JWTCache jwtCacheSize
+
   return authResult
+    where
+      observer = getObserver appState
+      jwtCache = getJwtCache appState
 
 -- Used to extract JWT exp claim and add to JWT Cache
 getTimeSpec :: AuthResult -> Int -> UTCTime -> Maybe TimeSpec

src/PostgREST/Metrics.hs

@@ -1,5 +1,5 @@
 {-|
-Module      : PostgREST.Logger
+Module      : PostgREST.Metrics
 Description : Metrics based on the Observation module. See Observation.hs.
 -}
 module PostgREST.Metrics
@@ -19,7 +19,7 @@ import PostgREST.Observation
 import Protolude
 
 data MetricsState =
-  MetricsState Counter Gauge Gauge Gauge (Vector Label1 Counter) Gauge
+  MetricsState Counter Gauge Gauge Gauge (Vector Label1 Counter) Gauge Gauge
 
 init :: Int -> IO MetricsState
 init configDbPoolSize = do
@@ -29,12 +29,13 @@ init configDbPoolSize = do
   poolMaxSize <- register $ gauge (Info "pgrst_db_pool_max" "Max pool connections")
   schemaCacheLoads <- register $ vector "status" $ counter (Info "pgrst_schema_cache_loads_total" "The total number of times the schema cache was loaded")
   schemaCacheQueryTime <- register $ gauge (Info "pgrst_schema_cache_query_time_seconds" "The query time in seconds of the last schema cache load")
+  jwtCacheSize <- register $ gauge (Info "pgrst_jwt_cache_size" "The number of cached JWTs")
   setGauge poolMaxSize (fromIntegral configDbPoolSize)
-  pure $ MetricsState poolTimeouts poolAvailable poolWaiting poolMaxSize schemaCacheLoads schemaCacheQueryTime
+  pure $ MetricsState poolTimeouts poolAvailable poolWaiting poolMaxSize schemaCacheLoads schemaCacheQueryTime jwtCacheSize
 
 -- Only some observations are used as metrics
 observationMetrics :: MetricsState -> ObservationHandler
-observationMetrics (MetricsState poolTimeouts poolAvailable poolWaiting _ schemaCacheLoads schemaCacheQueryTime) obs = case obs of
+observationMetrics (MetricsState poolTimeouts poolAvailable poolWaiting _ schemaCacheLoads schemaCacheQueryTime jwtCacheSize) obs = case obs of
   (PoolAcqTimeoutObs _) -> do
     incCounter poolTimeouts
   (HasqlPoolObs (SQL.ConnectionObservation _ status)) -> case status of
@@ -54,6 +55,8 @@ observationMetrics (MetricsState poolTimeouts poolAvailable poolWaiting _ schema
     setGauge schemaCacheQueryTime resTime
   SchemaCacheErrorObs _ -> do
     withLabel schemaCacheLoads "FAIL" incCounter
+  JWTCache cacheSize -> do
+    setGauge jwtCacheSize $ fromIntegral cacheSize
   _ ->
     pure ()
 

src/PostgREST/Observation.hs

@@ -57,8 +57,13 @@ data Observation
   | HasqlPoolObs SQL.Observation
   | PoolRequest
   | PoolRequestFullfilled
+  | JWTCache Int
 
-data ObsFatalError = ServerAuthError | ServerPgrstBug | ServerError42P05 | ServerError08P01
+data ObsFatalError
+  = ServerAuthError
+  | ServerPgrstBug
+  | ServerError42P05
+  | ServerError08P01
 
 type ObservationHandler = Observation -> IO ()
 

test/io/test_io.py

@@ -1632,6 +1632,8 @@ def test_admin_metrics(defaultenv):
         assert "pgrst_db_pool_available" in response.text
         assert "pgrst_db_pool_timeouts_total" in response.text
 
+        assert "pgrst_jwt_cache_size" in response.text
+
 
 def test_schema_cache_startup_load_with_in_db_config(defaultenv, metapostgrest):
     "verify that the Schema Cache loads correctly at startup, using the in-db `pgrst.db_schemas` config"