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Auto Scale

Auto-scaling is a crucial technique for effective load management of service traffic. It enables service operators to automatically adjust the number of instances or resources allocated to a service based on current or expected demand and resource utilization. By doing so, auto-scaling ensures that a service can handle incoming load while optimizing the cost of running the service by allocating just the right number of resources.

Auto-scale is a core integration in Aperture that works hand in hand with the flow control capabilities to provide a comprehensive load management platform. Aperture policies allow defining auto-scaler(s) that consider the flow control state for informed scaling decisions. For example, during sudden traffic spikes, if a load scheduler on a service sheds traffic, auto-scaler can automatically add more instances to the service to handle the increased load.

With the auto-scale capability in Aperture, service operators can configure auto-scaling policies based on different service overload signals, such as load shedding, in addition to resource utilization based on CPU, memory usage, network I/O, and so on. This flexibility enables service operators to fine-tune the auto-scaling behavior based on their specific service needs. Auto-scaling policies can be set up to add or remove instances or resources based on these signals, allowing for dynamic scaling in response to changing traffic patterns.

Auto-scaling is a powerful technique that enables service operators to maintain service availability and performance while optimizing costs. In Aperture, auto-scaling is an integral component of the load management platform, working seamlessly with flow control to provide a comprehensive solution. These capabilities allow services to dynamically adjust to incoming traffic patterns, ensuring optimal performance while minimizing infrastructure costs.


Aperture Agents interface with cloud infrastructure APIs, such as Kubernetes API, to discover, monitor, and scale infrastructure resources. The Aperture Controller uses the information from the Agents to make informed auto-scaling decisions that are then acted on by the Agents.

In an agent group, the leader Agent is responsible for interfacing with the cloud infrastructure APIs. For example, by maintaining a watch on scalable Kubernetes resources, the agent group leader can monitor changes to the resource status, such as the number of replicas configured and currently deployed. The up-to-date information is then used by the Aperture Controller to make informed auto-scaling decisions.

graph TD InfrastructureAPIs["Infrastructure APIs"]<-->AgentGroupLeader["Agent Group Leader"] AgentGroupLeader<-->Etcd["Aperture etcd"] Etcd<-->Controller["Aperture Controller"]

Auto Scaler

Auto Scaler is a high-level component in Aperture that performs auto-scaling. It can interface with infrastructure APIs such as Kubernetes to automatically adjust the number of instances or resources allocated to a service to meet changing workload demands. Auto Scaler is designed to ensure that the service is scaled out to meet demand and scaled in when demand is low. Scaling out is done more aggressively than scaling in to ensure optimal performance and availability.

  • Controllers: Auto Scaler leverages controllers (for example, Gradient Controller) to make scaling decisions. A Controller can be configured for either scaling in or out, and defines the criteria that determine when to scale. Controllers process one or more input signals to compute a desired scale value. By configuring Controllers, you can fine-tune the auto-scaling behavior to meet the specific scaling of a service. See Gradient Controller for more details.
  • A scale-in Controller is active only when its output is smaller than the actual scale value. A scale-out Controller is active only when its output is larger than the actual scale value. For example, the actual number of replicas of a Kubernetes Deployment. An inactive Controller does not contribute to the scaling decision.
  • Scale decisions from multiple active Controllers are combined by the Auto Scaler by taking the largest scale value.
  • Maximum scale-in and scale-out step sizes: The amount of scaling that happens at a time is limited by the maximum scale-in and scale-out step sizes. This is to prevent large-scale changes from happening at once.
  • Cooldown periods: There are cooldown periods defined individually for scale-out and scale-in. The Auto Scaler won't scale-out or scale-in again until the cooldown period has elapsed. The intention of cooldowns is to make the changes gradually and observe their effect to prevent overdoing either scale-in or scale-out.
    • Scale-in cooldown: The Auto Scaler won't scale-in again until the cooldown period has elapsed. If there is a scale-out decision, it is allowed to proceed, effectively resetting the scale-in cooldown. Essentially, scale out is given a higher priority than scale in to maintain safe operations.
    • Scale-out cooldown: The Auto Scaler won't scale-out again until the cooldown period has elapsed. If there is a scale-out decision which is much larger than the current scale value, the scale-out cooldown is reset. This is done to accommodate any urgent need for scale-out.

Gradient Controller

The Gradient Controller computes a desired scale value based on a signal and setpoint. The gradient controller tries to adjust the scale value proportionally to the relative difference between setpoint and signal.

The gradient describes a corrective factor that should be applied to the scale value to get the signal closer to the setpoint. It's computed as follows:

gradient=(signalsetpoint)slope\text{gradient} = \left(\frac{\text{signal}}{\text{setpoint}}\right)^{\text{slope}}

gradient is then clamped to [1.0, max_gradient] range for the scale-out controller and [min_gradient, 1.0] range for the scale-in controller.

The output of the gradient controller is computed as follows:

desired_scale=gradientclampedactual_scale.\text{desired\_scale} = \text{gradient}_{\text{clamped}} \cdot \text{actual\_scale}.

Pod Scaler

Pod Scaler is a basic building block of an auto-scaling policy for Kubernetes. It can scale out or scale in a Kubernetes Resources such as a Deployment. The component takes the desired replicas as an input signal and scales the underlying resources based on the value of the signal. To complete the feedback loop, the component emits output signals for the number of configured replicas and the actual number of replicas deployed.

A Pod Scaler component can be used standalone, but is not required to be defined explicitly if the high-level Auto Scaler component is used. Auto Scaler component allows multiple scale in, scale out controllers and takes care of instantiating the Pod Scaler component internally.

Kubernetes Object Selector

Kubernetes Object Selectors are used by auto-scaling components in a policy, such as Pod Scaler or Auto Scaler. A Kubernetes Object Selector identifies a resource in the Kubernetes cluster.

A Kubernetes Object Selector consists of:

  • Agent Group: The agent group identifies Aperture Agents where the component gets applied.
  • API Version: The Kubernetes API version of the resource.
  • Kind: The Kind of the Kubernetes resource, such as Deployment, ReplicaSet, StatefulSet.
  • Name: The name of the Kubernetes resource.
  • Namespace: The Kubernetes namespace of the resource.

Live Preview of Kubernetes Control Points

The Kubernetes resources identified by a Kubernetes Object Selector are called Kubernetes Control Points. These are a subset of resources in a Kubernetes cluster resource that can be scaled in or out. Aperture Agents perform automated discovery of Kubernetes Control Points in a cluster.

Use the aperturectl auto-scale control-points CLI command to list active control points.

For example:

aperturectl auto-scale control-points --kube


AGENT GROUP   NAME                                                NAMESPACE             KIND
default coredns kube-system Deployment
default coredns-5d78c9869d kube-system ReplicaSet
default gateway istio-system Deployment
default gateway-868c757988 istio-system ReplicaSet
default istiod istio-system Deployment
default istiod-6d9df7fb7 istio-system ReplicaSet
default local-path-provisioner local-path-storage Deployment
default local-path-provisioner-6bc4bddd6b local-path-storage ReplicaSet
default service1-demo-app demoapp Deployment
default service1-demo-app-7b4bc9bdcd demoapp ReplicaSet
default service2-demo-app demoapp Deployment
default service2-demo-app-677bb57574 demoapp ReplicaSet
default service3-demo-app demoapp Deployment
default service3-demo-app-58656dcf95 demoapp ReplicaSet
default wavepool-generator demoapp Deployment
default wavepool-generator-5b4578bdd9 demoapp ReplicaSet