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Load Balancer Support Tests

Introduction

This document describes how drivers should create load balanced clusters for testing and how tests should be executed for such clusters.

Testing Requirements

For each server version that supports load balanced clusters, drivers MUST add two Evergreen tasks: one with a sharded cluster with both authentication and TLS enabled and one with a sharded cluster with authentication and TLS disabled. In each task, the sharded cluster MUST be configured with two mongos nodes running on localhost ports 27017 and 27018. The shard and config servers may run on any free ports. Each task MUST also start up two TCP load balancers operating in round-robin mode: one fronting both mongos servers and one fronting a single mongos.

Load Balancer Configuration

Drivers MUST use the run-load-balancer.sh script in drivers-evergreen-tools to start the TCP load balancers for Evergreen tasks. This script MUST be run after the backing sharded cluster has already been started. The script writes the URIs of the load balancers to a YAML expansions file, which can be read by drivers via the expansions.update Evergreen command. This will store the URIs into the SINGLE_MONGOS_LB_URI and MULTI_MONGOS_LB_URI environment variables.

Test Runner Configuration

If the backing sharded cluster is configured with TLS enabled, drivers MUST add the relevant TLS options to both SINGLE_MONGOS_LB_URI and MULTI_MONGOS_LB_URI to ensure that test clients can connect to the cluster. Drivers MUST use the final URI stored in SINGLE_MONGOS_LB_URI (with additional TLS options if required) to configure internal clients for test runners (e.g. the internal MongoClient described by the Unified Test Format spec).

In addition to modifying load balancer URIs, drivers MUST also mock server support for returning a serviceId field in hello or legacy hello command responses when running tests against a load-balanced cluster. This can be done by using the value of topologyVersion.processId to set serviceId. This MUST be done for all connections established by the test runner, including those made by any internal clients.

Tests

The YAML and JSON files in this directory contain platform-independent tests written in the Unified Test Format. Drivers MUST run the following test suites against a load balanced cluster:

  1. All test suites written in the Unified Test Format
  2. Retryable Reads
  3. Retryable Writes
  4. Change Streams
  5. Initial DNS Seedlist Discovery