Hi-sap: Secure and Scalable Web Server System for Shared Hosting Services

We propose Hi-sap, a Web server system that solves internal security problems in a server used for shared hosting services and that achieves high site-number scalability with little performance degradation. Customers are often exposed to internal attacks, i.e., malicious customers illegally access other customers’ files. Existing approaches solve a portion of this problem, but they are not enough from the view point of performance, site-number scalability, or generality. The proposed system protects customers’ files by isolating them in separate security domains, “partitions” that are unit of protection, using a secure OS facility. A default partition is a Web site, and each partition has a Web server instance that runs under the privilege of an individual user and serves files in the partition. Since the Web servers reuse server processes and can run without the burden of a security mechanism themselves, there is little performance degradation. In addition, since Hi-sap dynamically controls the number of Web servers, the number of partitions in a server is scalable. We implemented Hi-sap on a Linux OS and evaluated its effectiveness. Experimental results show that Hi-sap has up to 14.3 times the performance of suEXEC and achieves high scalability of 1000 sites per server.