Fail fast if cannot connect to the MongoDB server on startup

turms-server-common/src/main/java/im/turms/server/common/storage/mongo/MongoContext.java

@@ -34,7 +34,6 @@
 import com.mongodb.reactivestreams.client.MongoClients;
 import com.mongodb.reactivestreams.client.MongoCollection;
 import com.mongodb.reactivestreams.client.MongoDatabase;
-import io.lettuce.core.internal.Futures;
 import io.netty.buffer.PooledByteBufAllocator;
 import io.netty.channel.nio.NioEventLoopGroup;
 import io.netty.channel.socket.nio.NioSocketChannel;

turms-server-common/src/main/java/im/turms/server/common/storage/mongo/TurmsMongoClient.java

@@ -94,13 +94,18 @@ private TurmsMongoClient(
                 verifyServers(descriptions, name, requiredClusterTypes);
                 connect.tryEmitValue(null);
             } catch (Exception e) {
-                Sinks.EmitResult result = connect.tryEmitError(e);
-                if (result.isFailure()) {
-                    LOGGER.fatal(e.getMessage());
-                }
+                connect.tryEmitError(e);
             }
         });
         operations = new TurmsMongoOperations(context);
+        // Ping the server to check if the connection is available, and the server is alive quickly.
+        operations.ping()
+                .subscribe(null,
+                        t -> connect.tryEmitError(new RuntimeException(
+                                "Failed to ping the server for the mongo client: \""
+                                        + name
+                                        + "\"",
+                                t)));
     }
 
     public Mono<Void> destroy(long timeoutMillis) {

turms-server-common/src/main/java/im/turms/server/common/storage/mongo/operation/MongoOperationsSupport.java

@@ -179,10 +179,11 @@ Mono<Void> updateJsonSchema(
 
     <T> Mono<T> inTransaction(Function<ClientSession, Mono<T>> execute);
 
+    Mono<Boolean> ping();
+
     Mono<Void> disableBalancing(String collectionName);
 
     Mono<Void> enableBalancing(String collectionName);
 
     Mono<Boolean> isBalancerRunning();
-
 }

turms-server-common/src/main/java/im/turms/server/common/storage/mongo/operation/TurmsMongoOperations.java

@@ -146,6 +146,10 @@ public class TurmsMongoOperations implements MongoOperationsSupport {
                     .append("as", new BsonString("a"))
                     .append("in", new BsonString("$$a.k")));
 
+    // Diagnostics
+    private static final BsonDocument PING_COMMAND =
+            new BsonDocument("ping", BsonPool.BSON_INT32_1);
+
     private final MongoContext context;
     private final Map<Class<?>, MongoOperationPublisher<?>> publisherMap =
             new NonBlockingIdentityHashMap<>(32);
@@ -891,6 +895,16 @@ public <T> Mono<T> inTransaction(Function<ClientSession, Mono<T>> action) {
                 ClientSession::commitTransaction);
     }
 
+    // Health Check
+
+    @Override
+    public Mono<Boolean> ping() {
+        return Mono.from(context.getDatabase()
+                .runCommand(PING_COMMAND, BsonDocument.class))
+                .map(document -> document.getNumber("ok")
+                        .intValue() == 1);
+    }
+
     // Balancer
 
     @Override