To ensure security, cloud service providers employ security groups as a key tool for cloud tenants to protect their virtual machines from unwanted traffic. However, security groups can be complex and often hard to configure, which may result in security vulnerabilities that impact the entire cloud platform. To assist tenants in designing better security groups, in this paper, we propose and develop a system called Secgras. Secgras enables tenants to visualize and hence to understand the static and dynamic access relations among virtual machine (VM) instances. Secgras also helps diagnose potential misconfigurations and provides suggestions to refine security group configurations based on real traffic traversing tenants VMs.