Hello @kuniaki_shindo,
Welcome to the community.
SonarCloud.io is hosted on AWS and it is not possible to assign Elastic IP address (persistent) to Load Balancers. This has not been a common request from customers but I understand your need.
AWS does suggest solutions to this problem so I will raise it with the product team to get it added to the list.
Have you tried SonarQube?
Kind regards,
Mark