Node Redis connection working locally but not on Azure

I am hosting both a Web App and a Redis Cache Instance on Microsoft Azure. The connection should be pretty straightforward.

var redis = require('redis');
client = redis.createClient(6379, 'somedomain.redis.cache.windows.net');
client.auth('asecret');

I can connect fine locally, but whenever I connect on Azure I get the following error:

Unaught exception: Error: Redis connection to somedomain.redis.cache.windows.net:6379 failed - connect EADDRNOTAVAIL
  at RedisClient.on_error (D:\home\site\wwwroot\node_modules\redis\index.js:196:24)

This problem hasn't occurred in the past and I've deployed to Azure countless times- it seems to have just randomly appeared. What on earth am I missing? I'm tearing out my hair over this problem.