Getting Started with Citrix ADC
Deploy a Citrix ADC VPX instance
Optimize Citrix ADC VPX performance on VMware ESX, Linux KVM, and Citrix Hypervisors
Apply Citrix ADC VPX configurations at the first boot of the Citrix ADC appliance in cloud
Install a Citrix ADC VPX instance on Microsoft Hyper-V servers
Install a Citrix ADC VPX instance on Linux-KVM platform
Prerequisites for Installing Citrix ADC VPX Virtual Appliances on Linux-KVM Platform
Provisioning the Citrix ADC Virtual Appliance by using OpenStack
Provisioning the Citrix ADC Virtual Appliance by using the Virtual Machine Manager
Configuring Citrix ADC Virtual Appliances to Use SR-IOV Network Interface
Configuring Citrix ADC Virtual Appliances to use PCI Passthrough Network Interface
Provisioning the Citrix ADC Virtual Appliance by using the virsh Program
Provisioning the Citrix ADC Virtual Appliance with SR-IOV, on OpenStack
Configuring a Citrix ADC VPX Instance on KVM to Use OVS DPDK-Based Host Interfaces
Deploy a Citrix ADC VPX instance on AWS
Deploy a VPX high-availability pair with elastic IP addresses across different AWS zones
Deploy a VPX high-availability pair with private IP addresses across different AWS zones
Configure a Citrix ADC VPX instance to use SR-IOV network interface
Configure a Citrix ADC VPX instance to use Enhanced Networking with AWS ENA
Deploy a Citrix ADC VPX instance on Microsoft Azure
Network architecture for Citrix ADC VPX instances on Microsoft Azure
Configure multiple IP addresses for a Citrix ADC VPX standalone instance
Configure a high-availability setup with multiple IP addresses and NICs
Configure a high-availability setup with multiple IP addresses and NICs by using PowerShell commands
Configure a Citrix ADC VPX instance to use Azure accelerated networking
配置HA-INC节点使用Citrix高availability template for internet-facing applications
Configure a high-availability setup with Azure external and internal load balancers simultaneously
Configure address pools (IIP) for a Citrix Gateway appliance
Upgrade and downgrade a Citrix ADC appliance
Solutions for Telecom Service Providers
Load Balance Control-Plane Traffic that is based on Diameter, SIP, and SMPP Protocols
Provide Subscriber Load Distribution Using GSLB Across Core-Networks of a Telecom Service Provider
Authentication, authorization, and auditing application traffic
Basic components of authentication, authorization, and auditing configuration
On-premises Citrix Gateway as an identity provider to Citrix Cloud
Authentication, authorization, and auditing configuration for commonly used protocols
Troubleshoot authentication and authorization related issues
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Persistence and persistent connections
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Gradually stepping up the load on a new service with virtual server–level slow start
Protect applications on protected servers against traffic surges
Retrieve location details from user IP address using geolocation database
Use source IP address of the client when connecting to the server
Use client source IP address for backend communication in a v4-v6 load balancing configuration
Set a limit on number of requests per connection to the server
Configure automatic state transition based on percentage health of bound services
Use case 2: Configure rule based persistence based on a name-value pair in a TCP byte stream
Use case 3: Configure load balancing in direct server return mode
Use case 6: Configure load balancing in DSR mode for IPv6 networks by using the TOS field
Use case 7: Configure load balancing in DSR mode by using IP Over IP
Use case 10: Load balancing of intrusion detection system servers
Use case 11: Isolating network traffic using listen policies
Use case 12: Configure Citrix Virtual Desktops for load balancing
Use case 13: Configure Citrix Virtual Apps for load balancing
Use case 14: ShareFile wizard for load balancing Citrix ShareFile
Use case 15: Configure layer 4 load balancing on the Citrix ADC appliance
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Authentication and authorization for System Users
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Configuring a CloudBridge Connector Tunnel between two Datacenters
Configuring CloudBridge Connector between Datacenter and AWS Cloud
Configuring a CloudBridge Connector Tunnel Between a Datacenter and Azure Cloud
Configuring CloudBridge Connector Tunnel between Datacenter and SoftLayer Enterprise Cloud
Configuring a CloudBridge Connector Tunnel Between a Citrix ADC Appliance and Cisco IOS Device
CloudBridge Connector Tunnel Diagnostics and Troubleshooting
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Least connection method
When a virtual server is configured to use the least connection load balancing algorithm (or method), it selects the service with the fewest active connections. This is the default method, because, in most circumstances, it provides the best performance.
For TCP, HTTP, HTTPS, and SSL_TCP services, the Citrix ADC appliance includes the following connection types in its list of existing connections:
- Active connections to a service.Connections representing requests that a client has sent to the virtual server and that the virtual server has forwarded to a service. For HTTP and HTTPS services, active connections represent only those HTTP or HTTPS requests that have not yet received a response.
- Waiting connections in the surge queue.Any connections to the virtual server that are waiting in a surge queue and have not yet been forwarded to a service. Connections can build up in the surge queue at any time, for any of the following reasons:
- Your services have connection limits, and all services in your load balancing configuration are at that limit.
- The surge protection feature is configured and has been activated by a surge in requests to the virtual server.
- The load-balanced server has reached an internal limit and therefore does not open any new connections. (For example, an Apache server’s connection limit is reached.)
When a virtual server uses the least connection method, it considers the waiting connections as belonging to the specific service. Therefore, it does not open new connections to those services.
For UDP services, the connections that the least connection algorithm considers include all sessions between the client and a service. These sessions are logical, time-based entities. When the first UDP packet in a session arrives, the Citrix ADC appliance creates a session between the source IP address and port and the destination IP address and port.
For Real-Time Streaming Protocol (RTSP) connections, the Citrix ADC appliance uses the number of active control connections to determine the lowest number of connections to an RTSP service.
The following example shows how a virtual server selects a service for load balancing by using the least connection method. Consider the following three services:
- Service-HTTP-1 is handling 3 active transactions.
- Service-HTTP-2 is handling 15 active transactions.
- Service-HTTP-3 is not handling any active transactions.
The following diagram illustrates how the Citrix ADC appliance forwards incoming requests when using the least connection method.
Figure 1. Mechanism of the Least Connections Load Balancing Method
In this diagram, the virtual server selects the service for each incoming connection by choosing the server with the fewest active transactions.
Connections are forwarded as follows:
Service-HTTP-3 receives the first request, because it is not handling any active transactions.
Note: The service with no active transaction is selected first.
Service-HTTP-3 receives the second and third requests because the service has the next least number of active transactions.
Service-HTTP-1 receives the fourth request because Service-HTTP-1 and Service-HTTP-3 have the same number of active transactions, the virtual server uses the round robin method to choose between them.
Service-HTTP-3 receives the fifth request.
Service-HTTP-1 receives the sixth request, and so on, until both Service-HTTP-1 and Service-HTTP-3 are handling the same number of requests as Service-HTTP-2. Then, the Citrix ADC appliance starts forwarding requests to Service-HTTP-2 when it is the least loaded service or its turn comes up in the round robin queue.
Note: If connections to Service-HTTP-2 close, it might get new connections before each of the other two services has 15 active transactions.
下表说明了如何连接是distributed in the three-service load balancing setup described earlier.
传入的连接 | Service Selected | Current Number of Active Connections | Remarks |
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Request-1 | Service-HTTP-3; (N = 0) | 1 | Service-HTTP-3 has the fewest active connections. |
Request-2 | Service-HTTP-3; (N = 1) | 2 | Service-HTTP-3 has the fewest active connections. |
Request-3 | Service-HTTP-3; (N = 2) | 3 | - |
Request-4 | Service-HTTP-1; (N = 3) | 4 | Service-HTTP-1 and Service-HTTP-3 have the same number of active connections. |
Request-5 | Service-HTTP-3; (N = 3) | 4 | Service-HTTP-1 and Service-HTTP-3 have the same number of active connections. |
Request-6 | Service-HTTP-1;(N = 4) | 5 | - |
Request-7 | Service-HTTP-3; (N = 4) | 5 | - |
Request-8 | Service-HTTP-1; (N = 5) | 6 | - |
Service-HTTP-2 is selected for load balancing when it completes its active transactions and the current connections to it close, or when the other services (Service-HTTP-1 and Service-HTTP-3) have 15 or more connections each.
The Citrix ADC appliance can also use the least connection method when weights are assigned to services. It selects a service by using the value (Nw) of the following expression:
Nw = (Number of active transactions) * (10000 / weight)
The following example shows how the Citrix ADC appliance selects a service for load balancing by using the least connection method when weights are assigned to services. In the preceding example, suppose Service-HTTP-1 is assigned a weight of 2, Service-HTTP-2 is assigned a weight of 3, and Service-HTTP-3 is assigned a weight of 4. Connections are forwarded as follows:
Service-HTTP-3 receives the first because the service is not handling any active transactions.
Note: If the services are not handling any active transactions, the Citrix ADC appliance uses the round robin method regardless of the weights assigned to each of the services.
Service-HTTP-3 receives the second, third, fourth, fifth, sixth, and seventh requests because the service has the lowest Nw value.
Service-HTTP-1 receives the eighth request. Because Service-HTTP-1 and Service-HTTP-3 now have the same Nw value, the appliance performs load balancing in a round robin manner. Therefore, Service-HTTP-3 receives the ninth request.
下表说明了如何连接是distributed on the three-service load balancing setup that is described earlier.
Request Received | Service Selected | Current Nw (Number of active transactions) * (10000 / weight) value | Remarks |
---|---|---|---|
Request-1 | Service-HTTP-3; (Nw = 0) | Nw = 2500 | Service-HTTP-3 has the lowest Nw value. |
Request-2 | Service-HTTP-3; (Nw = 2500) | Nw = 5000 | |
Request-3 | Service-HTTP-3; (Nw = 5000) | Nw = 7500 | |
Request-4 | Service-HTTP-3; (Nw = 7500) | Nw = 10000 | |
Request-5 | Service-HTTP-3; (Nw = 10000) | Nw = 12500 | |
Request-6 | Service-HTTP-3; (Nw = 12500) | Nw = 15000 | |
Request-7 | Service-HTTP-1; (Nw = 15000) | Nw = 20000 | Service-HTTP-1 and Service-HTTP-3 have the same Nw values |
Request-8 | Service-HTTP-3; (Nw = 15000) | Nw = 17500 |
Service-HTTP-2 is selected for load balancing when it completes its active transactions or when the Nw value of other services (Service-HTTP-1 and Service-HTTP-3) is equal to 50000.
The following diagram illustrates how the Citrix ADC appliance uses the least connection method when weights are assigned to the services.
Figure 2. Mechanism of the Least Connections Load Balancing Method when Weights are Assigned
To configure the least connection method, seeConfiguring a Load Balancing Method that Does Not Include a Policy.
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