The Cisco® ACE Application Control Engine solution enhances application availability and uptime by solving challenges posed in today's application environments.
• Scalability: The Cisco ACE allows scaling of applications and devices, and the scaling is transparent to the user. New applications can be added to the load-balanced pool, or a new service can be introduced without any disruption to the user.
• Health checking: The Cisco ACE provides active health checking by implementing a proactive health monitoring probe mechanism to help ensure high availability and increase the reliability of the application. This health monitoring mechanism can check the status of the application and remove an application server from the load-balanced pool if the application becomes unresponsive or fails to return the correct status code. The Cisco ACE sends messages to the servers and looks for certain expected results in return. Active health checking is useful for more complex types of verification, such as verification of the availability of the database that a particular Java Servlet relies on to perform its functions. In addition, scripting functions allow the operator to customize active health checking for applications for which preprogrammed capabilities do not exist. Active health checks are performed at regular intervals.
• Availability and reliability: The Cisco ACE Module uses a highly robust architecture consisting of multiple redundant network processors. The architecture provides separation of the control path and data path, helping ensure that device control and connection management are separated and that a high rate of load-balanced traffic will not affect health monitoring or high availability.
• Virtual device redundancy: The Cisco ACE can be configured to provide redundancy between two Cisco ACE Modules in the same Cisco Catalyst® 6500 Series Switch chassis or in two different chassis. The Cisco ACE also supports redundancy between two appliance form factor devices. In contrast to traditional solutions, the Cisco ACE supports high availability at both the physical and virtual device levels. The Cisco ACE device can be partitioned into up to 256 virtual devices, each with its own configuration files, resources, and management interfaces. The Cisco ACE provides the flexibility to configure redundancy only for selected virtual devices. For example, if a customer has consolidated the production and development environments of an application on the same Cisco ACE device but allocated separate virtual devices for each application environment because of security and other concerns, the customer can configure the Cisco ACE device to provide redundancy only for production environment.
• Active-active redundancy: The Cisco ACE supports flexible active-active redundancy configuration between two physical and virtual devices. This setup allows customers to distribute workload between both physical Cisco ACE devices rather than use only one of the devices in active mode. Figure 1 shows two physical Cisco ACE devices configured with four virtual devices. In this example, the virtual devices are evenly distributed between the two physical Cisco ACE devices. The letters A, B, C, and D represent the active virtual devices, and the primed letters A', B', C', and D' represent standby virtual devices.
Figure 1. Physical and Virtual Device Redundancy
• Stateful failover: The Cisco ACE replicates flows on the active virtual device on the standby virtual device on a per-connection basis. The replicated flows contain all the flow-state information necessary for the standby virtual device to take over the flow if the active virtual device becomes unresponsive. If the active device becomes unresponsive, the replicated flow on the standby virtual device becomes active when the standby virtual device assumes ownership. The active flows on the formerly active virtual device transition to a standby state to fully back up the active flows on the newly active virtual device. Supported end-user applications do not need to reconnect to maintain the same network session during failover and failback. This stateful failover and failback redundancy feature of Cisco ACE provides transparent failover for applications without any effect on business during device failure.
• Tracking and failure detection: The Cisco ACE supports tracking and failure detection of several network items and performs transparent switchover from an active Cisco ACE physical or virtual device to a standby device if the tracked network devices become unresponsive. All active connections that exist at the time of the switchover continue uninterrupted on the new active device. When the failed tracked network device becomes available again, the Cisco ACE evaluates the priority between active and standby devices and performs transparent switchover to the original active device if the resulting priority of the standby device is greater than the priority of the active device. The Cisco ACE can be configured to track several network devices such as gateways or hosts, interfaces, and Hot Standby Router Protocol (HSRP) groups. For example, the Cisco ACE can track an HSRP group and perform transparent switchover from an active Cisco ACE device to a standby Cisco ACE device if the HSRP group is unresponsive. In this scenario, the Cisco ACE capability to track and switch over reduces traffic on the Inter-Switch Link (ISL) between two distribution layer switches.
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