From last 3-4 day my server cpu 100% use maximum time . No plugin are installed . Is this DDos attack ?
Looks like Amplification attack. https://www.incapsula.com/ddos/attack-glossary/dns-amplification.html
kindly block this IP range and check what happened you cloudflare in your site for preventing this type of attack.
This is a comment just to increase your post count and is considered as junk. Those IPs are spoofed so you are not able to see the real IPs to block. Cloudflare is used from people that have no idea what a ddos attack is. Before some years was helpful because the hackers was not so feet as today they are and cloudflare left there where it was before some years. The best option will be to filter your traffic via GRE-tunnel via Voxility server.
Thanks for solutions. I am also working with apache solr. In case of cpu or memory utilization first we need to check which service it using the most. If Apache then why ? Is there any config issue ? you can check conf file ,if you want to continue on apache.