:nxdomain when using redis cluster endpoint with large number of shards

[aniaptebsft]

This is with eredis_cluster ~> 0.5.12

When using eredis pointing to a redis cluster endpoint with large number of shards, I get error :nxdomain. The only workaround is to use a list of ip addresses.

It is because, :inet.getaddr/2 unable to handle dns lookups that result in a large answers. Note however that :inet_res.gethostbyname/1 works fine likely because it reissues the dns lookup over TCP when it finds that the first query had the truncate bit set.

Offending code here: https://github.com/wooga/eredis/blob/master/src/eredis_client.erl#L335 (line 335, and line 307)

Below is a sample iex output that shows the error
Note the :nxdomain error in the second command, same hostname works fine in the fourth command.

iex(tango@2e76e9718be1)69> :inet.getaddr('small-redis-cluster.kk5zzw.clustercfg.use1.cache.amazonaws.com', :inet)   
{:ok, {10, 99, 17, 14}}

iex(tango@2e76e9718be1)70> :inet.getaddr('large-redis-cluster.kk5zzw.clustercfg.use1.cache.amazonaws.com', :inet)         
{:error, :nxdomain}

iex(tango@2e76e9718be1)71> :inet_res.gethostbyname('small-redis-cluster.kk5zzw.clustercfg.use1.cache.amazonaws.com')
{:ok,
 {:hostent,
  'small-redis-cluster.kk5zzw.clustercfg.use1.cache.amazonaws.com', [],
  :inet, 4,
  [
    {10, 99, 23, 178},
    {10, 99, 31, 149},
    {10, 99, 22, 232},
    {10, 99, 6, 27},
    {10, 99, 17, 14},
    {10, 99, 1, 221},
    {10, 99, 2, 67},
    {10, 99, 1, 59}
  ]}}
  
iex(tango@2e76e9718be1)72> :inet_res.gethostbyname('large-redis-cluster.kk5zzw.clustercfg.use1.cache.amazonaws.com')      
{:ok,
 {:hostent, 'large-redis-cluster.kk5zzw.clustercfg.use1.cache.amazonaws.com', [],
  :inet, 4,
  [
    {10, 99, 59, 135},
    {10, 99, 57, 16},
    {10, 99, 59, 160},
    {10, 99, 56, 194},
    {10, 99, 56, 232},
    {10, 99, 57, 166},
    {10, 99, 57, 110},
    {10, 99, 60, 8},
    {10, 99, 57, 71},
    {10, 99, 59, 89},
    {10, 99, 57, 36},
    {10, 99, 59, 202},
    {10, 99, 56, 205},
    {10, 99, 57, 149},
    {10, 99, 59, 14},
    {10, 99, 59, 230},
    {10, 99, 61, 124},
    {10, 99, 61, 224},
    {10, 99, 60, 182},
    {10, 99, 60, 109}
  ]}}