I am having a self hosted game server hosted on google cloud using Ubuntu 14.04 everything was working fine but since last week a "Dos" attempt is made on gameserver or might be on VPS during which the cpu usage jumps to 100% and I see the rise in cpu usage due to the process "ksoftirq" also the ssh becomes unresponsive and server too. After 2-3 minutes or after restarting the server everything goes to normal. I can say its a DoS attempt because in google cloud monitoring I see rise in Incoming packets. I have upgraded the CPU to dual core and also RAM to 2 Gb but the issue cannot be solved. Tell me how can this dos attempt can be mitigated using Iptables or and script or how can I log the attackers IP to block it from panel.

There's not much you can do to prevent others from launching a DDoS attack at your server. Nevertheless, a web search for "mitigate ddos attack" will turn up a number of articles that you should find useful.

This one looks like a good place to start: https://www.wired.com/insights/2012/...os-mitigation/

Good article and written by someone at Incapsula.

The main thing that people generally fail to consider is that dealing with DDoS attacks on server "Oh, I've an IPTABLES firewall" is generally not particularly effective. If the connections are being made to the point that your on-server firewall is having to deal with it then your connection is likely to be swamped anyway.

External traffic filtering DDoS mitigation is highly effective and can generally handle pretty much any size of attack.

Having used Incapsula at a previous job I can recommend them and their mitigation is easy to implement.

i know i'm only nitpicking, but...surely it can't be both self-hosted AND cloud hosted?

Maybe it's a VPS on Google Cloud, not self-hosted, but self-managed.