MongoDB Atlas: C# driver connection with MongoClientSettings

C# driver + Atlas

using MongoDB.Driver;

var settings = MongoClientSettings.FromConnectionString(
    Environment.GetEnvironmentVariable("MONGODB_URI"));
settings.MaxConnectionPoolSize = 20;
settings.ServerSelectionTimeout = TimeSpan.FromSeconds(5);

var client = new MongoClient(settings);
// prove it at startup
await client.GetDatabase("admin").RunCommandAsync[BsonDocument](
    new BsonDocument("ping", 1));

Rules

• MongoClientSettings.FromConnectionString parses the Atlas SRV string, then you layer pool and timeout settings on top. Do not concatenate query params by hand.
• One MongoClient per app lifetime. It is thread-safe; the driver manages the pool internally.
• ServerSelectionTimeout of a few seconds turns network misconfig into a fast error with a useful message.
• Register the client as a singleton in your DI container. Scoped or transient registration recreates the pool constantly.
• On shutdown, dispose is handled by the container for singletons; for manual lifetimes call nothing special, just let the singleton die with the host.

Verify

The startup ping from the deploy network proves the URI, user, password, and IP access list entry.

C# driver MongoClientSettings pattern and Atlas connection prerequisites verified against https://www.mongodb.com/docs/manual/reference/connection-string/ and https://www.mongodb.com/docs/atlas/troubleshoot-connection/ on 2026-09-26.