ElasticSearch doesn't start after installing 5.6.4
The issue is you don't have 51.15.212.76 on your server. Your provider might map 51.15.212.76 -> 10.5.85.149
So try this instead
network.host: 10.5.85.149
Or better to bind to all interfaces
network.host: 0.0.0.0
I saw your update. You cannot use this configuration:
network.host: 51.15.212.76
because you have no network interface with this ip address.
You could use this 10.5.85.149 from eth0, for example.