Thiết lập và các tin nhắn clr là những công cụ mà các máy chủ gốc có thể sử dụng để làm như vậy. Đặt tin cập nhật các tiêu đề tương ứng với một đối tượngTài nguyên của đối tượng nhận dạng thống nhất. Các phiên bản HTTP được sử dụng để truy cập vào đối tượng. | 254 HTTP Essentials logical system as figure illustrates. Should one physical server fail the cluster continues to operate with the remaining systems. For static Web sites server clusters are generally not as desirable as local load balancing. Clusters are much more complex to administer and maintain and they are usually more expensive to deploy. For full effectiveness clustering also requires special support from applications in this case the Web server software. On the other hand clusters can play an important role in protecting dynamic Web applications as the next section discusses. Multi-Layer Security Architectures The previous section introduces firewalls as the primary technology for securing the perimeter of a Web site. Firewalls are also important for providing security within a site. Figure shows a typical security architecture for bullet-proof Web sites. As the figure shows firewalls create a multi-layer architecture by bracketing the site s Web servers. Exterior firewalls separate the Web servers from the Internet outside the site interior firewalls separate the Web server from database servers deeper within the site. By creating multiple layers this architecture adds more security to the core information that a Web site manages information in the site s database. The figure highlights the rules that each firewall contains. As long as the site is a public Web site the exterior firewall must allow anyone access to Figure Clustering bonds multiple physical systems together to act as one logical system. In most implementations the logical system can automatically recover from the failure of a physical system. Logical Server Building Bullet-Proof Web Sites 255 DMZ Only allow access to Web Server s Only allow access from Web Server s Exterior Firewall Interior Firewall Database Server Web Server Figure Web sites often employ a multi-tier firewall configuration dividing the site into a public the Internet a private protected .
