Solutions — Literature
alt="Resonate"> alt="Resonate">October 2000
Intranets, extranets, and the Internet are the lifelines of modern enterprises as mission-critical business activities become more dependent on geographically dispersed information, services, and computing resources. Across the global corporate network or over the Internet, employees and customers expect fast, reliable service for electronic mail (email), electronic commerce (e-commerce) and a host of other essential IP-based applications.
But as this distributed environment becomes more indispensable to business operations, its expanding complexities - from applications to geographies, networking infrastructures, server systems, and user bases - make its deployment and management increasingly difficult. Web masters, system/network administrators, and business managers struggle to match existing system resources with client requirements while trying to prepare for imminent and exponential increases in demand for global applications and services.
Resonate Global Dispatch™ is a WAN-based, multi-site, service level control solution that provides high availability and optimum performance for geographically distributed e-business applications. It enables multiple, dispersed points of presence (POPs) to act as a single, highly available system and directs user requests to the POP best able to maximize service levels. Additionally, it can enhance a user's experience by routing them to the POP with the content most relevant to their needs or it can direct intranet users to the POP closest to their location to save on WAN costs.
By gathering and using latency, load, and availability information, Global Dispatch software directs client requests to the physical site best suited to respond. As illustrated in Figure 1, Global Dispatch combines multiple physical sites into a single (or more, if needed) virtual hostname such as www.company.com or company.com. Clients use the virtual hostname to access resources that may be available across multiple physical sites.
When a client's local DNS server makes an address resolution request for a virtual hostname, Global Dispatch responds with the IP address of the most appropriate physical site based on the latency and load information it receives from Global Dispatch agents installed at each site. Global Dispatch uses the following metrics and policies to determine the site best suited to respond to client requests:
The intelligent scheduling capabilities and an easy-to-use management console enable administrators to efficiently direct requests across multiple sites and also accommodate diverse company requirements. Administrators gain control over geographically dispersed traffic to deliver the best experience to its users and to save costs by optimally allocating server resources and reducing traffic on private backbone WANs.
To effectively manage WAN traffic and server resources, Global Dispatch software integrates three major components: a Scheduler that receives and resolves client requests; agents that monitor and communicate physical POP status; and the Global Dispatch Manager console that allows configuration and gathering of site statistics. These three components integrate tightly to deliver a responsive system to maximize service levels for globally distributed traffic.
Global Dispatch Scheduler (item C in Figure 1) ensures that traffic is directed to the most available and appropriate site. The Global Dispatch Scheduler takes the client requests for the virtual hostname through the client's local DNS server and DNS hierarchy. It then directs the client to the most appropriate physical site by first determining the optimal site and then returning the IP address (or Virtual IP address) of that site.
A single IP address can be returned for the address resolution or multiple IP addresses can be returned for failover.
The Scheduler provides the intelligence to route clients around failed sites or to direct requests based on predefined rules and policies. These predefined rules allow Global Dispatch to send clients to sites that are closest in proximity, least loaded or offering the best response time. Global Dispatch observes the following policies, in order, when directing clients to the most appropriate site (shown in Figure 2):
If neither persistence or directed traffic features have been enabled, the Scheduler chooses a physical POP based on the latency and load information it receives from the Global Dispatch agents installed at each POP. The following load balancing rules can be selected in Global Dispatch (shown in Figure 3):
When latency measurements are chosen, Global Dispatch has the ability to take immediate action and send an IP address back to the local DNS server with round-robin without having to waiting for the latency measurements to be returned. This mode of operation is especially useful to provide a quick response to client requests while still enabling latency measurements to be factored into subsequent decisions. The Scheduler quickly returns an IP address back to the client's local DNS server with round-robin while latency measurements are performed in the background and stored in the cache for future requests.
This mode enables administrators to test the Global Dispatch configuration before putting it into actual production. In this mode, Global Dispatch software responds to DNS queries using a simple round-robin scheduling method. Simultaneously, it logs the results of "what-if" calculations to show which POP would have been selected had certain rules been activated. Shadow Mode helps administrators better understand site traffic and routing patterns at initial site setup. Additionally, it provides a means to safely test adjustments that may be warranted because of fluctuations in site activity.
The Scheduler can be used in conjunction with the authoritative DNS servers either as a delegate to the authoritative server or it can act as a proxy to the authoritative DNS server to resolve A-records (common hostname request for IP address).
When Global Dispatch is a delegate of the authoritative server (show in Figure 4), hostnames such as www.domain.com, ftp.domain.com, are delegated as subdomains to Global Dispatch. The delegation redirects the client's local DNS server from the Authoritative DNS server to the Global Dispatch Scheduler for subdomains. For instance, when www.domain.com is requested, the authoritative DNS server redirects, or delegates, www.domain.com to be resolved by the Global Dispatch Scheduler. The Scheduler then responds to the client's local DNS server with the appropriate IP address. The authoritative DNS server will still handle the domain.com request, but will pass the sub.domain.com requests on to Global Dispatch.
When the Scheduler acts as a proxy to the authoritative DNS server (shown in Figure 5), it can also handle requests for domain.com and it is treated as a peer to the authoritative DNS server. It can resolve both domain.com requests and subdomain requests, such as www.domain.com. Any requests that cannot be resolved by Global Dispatch Scheduler in this mode will be requested from the authoritative DNS server and returned back to the Scheduler. This will include any non-A records, such as MX, PTR, etc. requests.
The Scheduler is able to direct incoming requests from the client's local DNS server to the appropriate site based on predefined policies giving administrators ultimate flexibility in directing traffic and delivering predictable service levels. The Global Dispatch Scheduler, however, does not act alone. It gathers site information from the Global Dispatch agent to aid in its decision making.
Global Dispatch Agents (item D in Figure 1) gather statistics from the physical sites to provide the Schedulers with site availability, load and response times to the client DNS servers. The agents are installed at each physical POP and are the Scheduler's point of contact for information about a POP. Agents can be loaded on any local server which allows the Global Dispatch Scheduler to work with any local traffic management solution including Resonate Central Dispatch™ sites, hardware-based load balanced sites, and sites hosted on a single Web server.
Each agent measures both the POP load and the latency between its POP and the client DNS server making the address resolution request. The agent, independent of DNS requests, periodically communicates load information to the Scheduler; while latency information is measured and communicated when initiated by a DNS latency request. If the load measurements cannot be completed during successive tries, the Scheduler will mark the site as down and will direct traffic to other sites. In addition, a single POP can have multiple agents, each carrying a share of the triangulation work (latency measurement) for that POP. This configuration minimizes scheduling overhead in the largest Internet environments and also prevents agents from being a single point of failure.
When measuring site load, Global Dispatch agents offer administrators tremendous flexibility in choosing the load calculation method that is most appropriate for individual site environments. Agents determine site load in one of the following ways (shown in Figure 6):
Global Dispatch Manager (shown in figure 8) enables administrators to quickly and easily set up, configure, and manage multiple, geographically distributed sites. The Global Dispatch Manager is a graphical console that gives administrators a single view into their Global Dispatch sites and allows management from local or remote locations. This tool enables administrators to quickly bring up a redundant site with an easy-to-use interface. Once the Global Dispatch sites are up and running, statistics can be gathered through the Global Dispatch Manager to provide valuable usage information that helps administrators troubleshoot and fine-tune the site configuration.
The Global Dispatch Manager has been created to facilitate quick configuration of redundant sites through basic and advanced configuration screens. With error checking, pull down menus and simple check boxes, companies can ensure their multi-site configuration is created quickly and easily from the start. For additional flexibility, all configuration and commands in the Global Dispatch Manager can be executed through a command line interface.
The Global Dispatch Manager and command line utilities also provide site statistics to enable administrators to quickly troubleshoot problems and to proactively monitor traffic patterns. The Global Dispatch statistics program queries the Scheduler for information; it counts and refreshes statistics, and flushes the Scheduler cache as requested. To provide important system management information to administrators, Global Dispatch statistics describe the health of POPs, as well as traffic and system efficiency. Global Dispatch logs the results of all DNS requests including the source IP address of the DNS query, the physical POP chosen, and the IP address returned. The Global Dispatch Manager provides easy access to the following available statistics (shown in Figure 9):
Global Dispatch statistics can be continuously displayed to provide on-going site evaluation.
All the Global Dispatch elements tie tightly together to provide the highest level of availability and performance to deliver the best user experience. When a client connects to a Web site, it must resolve the site name (e.g., www.resonate.com or resonate.com) to an IP address. This process is illustrated in Figure 10. The process steps include the following:
NOTE: Global Dispatch also supports multiple virtual host names at each POP, allowing fine granularity in directing traffic to meet varying browser access patterns or unique server configurations.
When a business is dependent on the successful access of data, a company can't afford an Internet site going down or slow response times. Resonate Global Dispatch provides a WAN-based, multi-site, service level control solution that provides high availability and optimum performance for geographically distributed e-business applications. The Global Dispatch Scheduler enables intelligent management of globally distributed traffic to ensure traffic is always directed to the most available, responsive sites while the agents gather the valuable site metrics that help in the decision making process. And, lastly the Global Dispatch Manager provides a single interface to configure, monitor and proactively manage distributed sites.
Resonate Global Dispatch is the only software solution that has been uniquely designed to provide high availability and scalability without compromising performance while still offering the greatest flexibility and control over geographically distributed traffic. Its flexible software solution layers onto existing infrastructure, including existing DNS and local server load balancing solutions, enabling companies to quickly and easily deploy a redundant site and ultimately deliver a great end user experience. Integrating with all of Resonate's products including Central Dispatch, Commander, and Enterprise Services Console, Resonate Global Dispatch ensures service levels can be easily controlled and maintained across multiple applications, services and geographies.
For more information on how Resonate can help you guarantee the end-user service levels of business-critical applications while cutting operating costs, contact a sales representative at or 408-545-5535.
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