Calculate best case scenario unidirectional latency and ping between AWS DCs

latencies.js

const toRadians = num => num * Math.PI / 180;

// Get the long, lat values for the desired dc 
module.exports.datacenters = {
  'ap-east-1':      [22.29,  114.16 ],
  'ap-northeast-1': [35.41,  139.42 ],
  'ap-northeast-2': [37.56,  126.98 ],
  'ap-northeast-3': [34.65,  136    ],
  'ap-south-1':     [19.08,  72.88  ],
  'ap-southeast-1': [1.37,   103.8  ],
  'ap-southeast-2': [-33.86, 151.2  ],
  
  'ca-central-1':   [45.5,   -73.6  ],
  
  'cn-north-1':     [39.92,  116.44 ],
  'cn-northwest-1': [38.49,  106.25 ],
  
  'eu-central-1':   [50,     8      ],
  'eu-north-1':     [59.33,  18.06  ],
  'eu-west-1':      [53,     -8     ],
  'eu-west-2':      [51,     -0.1   ],
  'eu-west-3':      [48.86,  2.35   ],
  
  'me-south-1':     [25.93,  50.64  ],
  
  'sa-east-1':      [-23.34, -46.38 ],
  
  'us-east-1':      [38.13,  -78.45 ],
  'us-east-2':      [39.96,  -83    ],
  'us-west-1':      [37.35,  -121.96],
  'us-west-2':      [46.15,  -123.88],
};

/**
 * Returns the distance in KM between coords/ dc names
 */
module.exports.distance = (dc1, dc2) => {
    const [lat1, lon1] = Array.isArray(dc1) ? dc1 : module.exports.datacenters[dc1];
    const [lat2, lon2] = Array.isArray(dc2) ? dc2 : module.exports.datacenters[dc2];

    // Calculate distance between points
    const R = 6371e3; // metres
    const φ1 = toRadians(lat1);
    const φ2 = toRadians(lat2);
    const Δφ = toRadians(lat2-lat1);
    const Δλ = toRadians(lon2-lon1);

    const a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
            Math.cos(φ1) * Math.cos(φ2) *
            Math.sin(Δλ/2) * Math.sin(Δλ/2);
    const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

    return (R * c / 1000);
}

/**
 * Returns minimal unidirectional latency in MS between coords or dc names (speed of light)
 */
module.exports.minLatency = (dc1, dc2) => {
    return module.exports.distance(dc1, dc2) * 0.00333564095198152;
}

/**
 * Return estimated optimal ping value between coords or dc names in MS
 */
module.exports.minPing = (dc1, dc2) => {
    // Calculate bi-directional time + OS + network hops
    // Hops ratio assumes AVG traffic distance traveled for a packet is 850Km for points geographically separated by 500Km
    const hopsRatio = 850 / 500;
    const uniLatency = module.exports.minLatency(dc1, dc2);
    return 1 + (uniLatency * hopsRatio) * 2;
}

The 850/500 ratio is a rough estimate. I'd have to dig into https://pdfs.semanticscholar.org/cd7c/e2525ef56f36949ba75761587e211b63785a.pdf to get the actual data.