Fix CosmosClient memory leak in CosmosDbFactory.GetCosmosClient

src/Scaler.Tests/CosmosDbFactoryTests.cs

@@ -0,0 +1,51 @@
+using System.Threading;
+using Microsoft.Azure.Cosmos;
+using Xunit;
+
+namespace Keda.CosmosDb.Scaler.Tests
+{
+    public class CosmosDbFactoryTests
+    {
+        private const string DummyConnection1 = "AccountEndpoint=https://example1.com:443/;AccountKey=ZHVtbXkx";
+        private const string DummyConnection2 = "AccountEndpoint=https://example2.com:443/;AccountKey=ZHVtbXky";
+
+        [Fact]
+        public void GetCosmosClient_OnlyConstructsOnceForSameKey()
+        {
+            var factory = new CountingCosmosDbFactory();
+
+            CosmosClient c1 = factory.GetCosmosClient(DummyConnection1, useCredentials: false, clientId: null);
+            CosmosClient c2 = factory.GetCosmosClient(DummyConnection1, useCredentials: false, clientId: null);
+            CosmosClient c3 = factory.GetCosmosClient(DummyConnection1, useCredentials: false, clientId: null);
+
+            Assert.Same(c1, c2);
+            Assert.Same(c2, c3);
+            Assert.Equal(1, factory.CreateCount);
+        }
+
+        [Fact]
+        public void GetCosmosClient_ConstructsOncePerDistinctKey()
+        {
+            var factory = new CountingCosmosDbFactory();
+
+            factory.GetCosmosClient(DummyConnection1, useCredentials: false, clientId: null);
+            factory.GetCosmosClient(DummyConnection2, useCredentials: false, clientId: null);
+            factory.GetCosmosClient(DummyConnection1, useCredentials: false, clientId: null);
+            factory.GetCosmosClient(DummyConnection2, useCredentials: false, clientId: null);
+
+            Assert.Equal(2, factory.CreateCount);
+        }
+
+        private sealed class CountingCosmosDbFactory : CosmosDbFactory
+        {
+            public int CreateCount;
+
+            protected internal override CosmosClient CreateCosmosClient(
+                string endpointOrConnection, bool useCredentials, string clientId)
+            {
+                Interlocked.Increment(ref CreateCount);
+                return base.CreateCosmosClient(endpointOrConnection, useCredentials, clientId);
+            }
+        }
+    }
+}

src/Scaler/Services/CosmosDbFactory.cs

@@ -5,7 +5,7 @@
 
 namespace Keda.CosmosDb.Scaler
 {
-    internal sealed class CosmosDbFactory
+    internal class CosmosDbFactory
     {
         private const string _applicationName = "keda-external-azure-cosmos-db";
         // As per https://docs.microsoft.com/dotnet/api/microsoft.azure.cosmos.cosmosclient, it is recommended to
@@ -14,10 +14,12 @@ internal sealed class CosmosDbFactory
 
         public CosmosClient GetCosmosClient(string endpointOrConnection, bool useCredentials, string clientId)
         {
-            return _cosmosClientCache.GetOrAdd((endpointOrConnection, clientId), CreateCosmosClient(endpointOrConnection, useCredentials, clientId));
+            return _cosmosClientCache.GetOrAdd(
+                (endpointOrConnection, clientId),
+                _ => CreateCosmosClient(endpointOrConnection, useCredentials, clientId));
         }
 
-        private CosmosClient CreateCosmosClient(string endpointOrConnection, bool useCredentials, string clientId)
+        protected internal virtual CosmosClient CreateCosmosClient(string endpointOrConnection, bool useCredentials, string clientId)
         {
             if (useCredentials)
             {