pub_mcrouter_cfg.txt

 {
   "pools": {
     "chicago": {
       "servers": ["10.X.X.1:11211","10.X.X.1:11212","10.X.X.2:11211","10.X.X.2:11212","10.X.X.3:11211","10.X.X.3:11212"]
     },
     "ashburn": {
       "servers": ["10.Y.Y.1:11211","10.Y.Y.1:11212","10.Y.Y.2:11211","10.Y.Y.2:11212","10.Y.Y.3:11211","10.Y.Y.3:11212"]
     }
   },
   "route": {
     "type": "PoolRoute",
     "pool": "chicago",
     "shadows": [
      {
        "target": "PoolRoute|ashburn",
        // shadow traffic that would go to all hosts in chicago pool
        "index_range": [0, 6],
        // shadow requests for 100% of keys based on key hash
        "key_fraction_range": [0, 1]
      }
     ]
   }
 }