AWS terminology

The following table provides a brief description of some of the autoscaling terms used in this document.

Terminology Description
AWS auto scaling group AWS auto scaling group is a collection of EC2 instances that share similar characteristics and are treated as a logical grouping for the purposes of instance scaling and management.
Amazon Machine Image (AMI) A machine image, which provides the information required to launch an instance, which is a virtual server in the cloud.
Elastic Compute Cloud (EC2) A web service that provides secure, resizable compute capacity in the cloud. It is designed to make web-scale cloud computing easier for developers.
Elastic IP (EIP) addresses An Elastic IP address is a static, public IPv4 address designed for dynamic cloud computing. You can associate an Elastic IP address with any instance or network interface for any VPC in your account.
Elastic network interface (ENI) A virtual network interface that you can attach to an instance in a VPC.
Instance type Amazon EC2 provides a wide selection of instance types optimized to fit different use cases. Instance types comprise varying combinations of CPU, memory, storage, and networking capacity and give you the flexibility to choose the appropriate mix of resources for your applications.
Identity and Access Management (IAM) role An AWS identity with permission policies that determine what the identity can and cannot do in AWS. You can use an IAM role to enable applications running on an EC2 instance to securely access your AWS resources.
IAM-instance-profile An identity provided to the Citrix ADC instances provisioned in a cluster in AWS. The profile allows the instances to access AWS services when it starts to load balance the client requests.
Listener A listener is a process that checks for connection requests, using the protocol and port that you configure. The rules that you define for a listener determine how the load balancer routes requests to the targets in one or more target groups.
NLB Network load balancer. NLB is an L4 load balancer available in the AWS environment.
Route 53 Route 53 is Amazon’s highly available and scalable cloud domain name system (DNS) web service.
Security groups A named set of allowed inbound network connections for an instance.
Subnets A segment of the IP address range of a VPC that EC2 instances can be attached to. You can create subnets to group instances according to security and operational needs.
Virtual Private Cloud (VPC) A web service for provisioning a logically isolated section of the AWS cloud where you can launch AWS resources in a virtual network that you define.

Citrix ADC VPX Autoscale terminology

The following table provides a brief description of some of the Citrix ADC VPX autoscaling terms used in this document.

Terminology Description
Autoscale groups Autoscale group is a group of Citrix ADC instances that load balance applications as a single entity and trigger autoscaling when the threshold parameters breach the limits. Citrix ADC instances scale-out or scale-in dynamically based on the Autoscale groups configuration. Note: Citrix Autoscale group is called Autoscale group throughout this document whereas the AWS Autoscale group is explicitly called AWS Autoscale group.
Citrix ADC clusters A Citrix ADC cluster is a group of Citrix ADC VPX instances and each instance is called a node. The client traffic is distributed across the nodes to provide high availability, high throughput, and scalability.
Drain connection timeout During scale-in, once an instance is selected for deprovisioning, Citrix Application Delivery and Management removes the instance from processing new connections to Autoscale group and waits until the specified drain connection timeout period expires before deprovisioning. This allows existing connections to this instance be drained out before it gets deprovisioned. If the connections are drained before the drain connection timeout expires, even then the Citrix Application Delivery and Management waits for the drain connection timeout period to expire before starting a new evaluation. Note: If the connections are not drained even after the drain connection timeout expires, the Citrix Application Delivery and Management removes the instances which might impact the application. Default value is 5 minutes and is configurable.
Cooldown period After a scale-out, the cooldown period is the time for which evaluation of the statistics has to be stopped. This ensures organic growing of an Autoscale group by allowing current traffic to stabilize and average out on the current set of instances before the next scaling decision is made. Default cooldown period value is 10 minutes and is configurable. Note: Default value is determined based on the time required for the system to stabilize after a scale-out (approximately 4 minutes) plus Citrix ADC configuration and DNS advertisement time.
Tags Each Autoscale group is assigned a tag which is a key and value pair. You can apply tags to the resources that enable you to organize and identify resources easily. The tags are applied to both AWS and Citrix Application Delivery and Management. Example: Key= name, Value = webserver. It is recommended to use a consistent set of tags to easily track the Autoscale groups that might belong to various groups such as development, production, testing.
Threshold parameters Parameters that are monitored for triggering scale-out or scale-in. The parameters are CPU usage, memory usage, and throughput. You can select one parameter or more than one parameter for monitoring.
Time to Live (TTL) Specifies the time interval that the DNS resource record might be cached before the source of the information must again be consulted. Default TTL value is 30 seconds and is configurable.
Watch time The time for which the scale parameter’s threshold has to stay breached for a scaling to happen. If the threshold is breached on all the samples collected in this specified time then a scaling happens. If the threshold parameters remain at a value higher than the maximum threshold value throughout this duration, a scale-out is triggered. If the threshold parameters operate at a value lower than the minimum threshold value, a scale-in is triggered. Default value is 3 minutes and is configurable.
AWS terminology