{
    "candidate_servers": [
        {
            "address": "a:27017", 
            "avg_rtt_ms": 5, 
            "tags": [
                {
                    "data_center": "dc"
                }
            ], 
            "type": "Standalone"
        }
    ], 
    "eligible_servers": [
        {
            "address": "a:27017", 
            "avg_rtt_ms": 5, 
            "tags": [
                {
                    "data_center": "dc"
                }
            ], 
            "type": "Standalone"
        }
    ], 
    "in_latency_window": [
        {
            "address": "a:27017", 
            "avg_rtt_ms": 5, 
            "tags": [
                {
                    "data_center": "dc"
                }
            ], 
            "type": "Standalone"
        }
    ], 
    "operation": "read", 
    "read_preference": {
        "mode": "SecondaryPreferred", 
        "tags": [
            {
                "data_center": "nyc"
            }
        ]
    }, 
    "suitable_servers": [
        {
            "address": "a:27017", 
            "avg_rtt_ms": 5, 
            "tags": [
                {
                    "data_center": "dc"
                }
            ], 
            "type": "Standalone"
        }
    ], 
    "topology_description": {
        "servers": [
            {
                "address": "a:27017", 
                "avg_rtt_ms": 5, 
                "tags": [
                    {
                        "data_center": "dc"
                    }
                ], 
                "type": "Standalone"
            }
        ], 
        "type": "Single"
    }
}