Autoscaling gateway agents

External gateway agents allow connectivity to be routed through gateways internally within your Kubernetes cluster or externally via an external endpoint. Typically, agents are included within the gateway configuration. As each pod replica is registered individually as a resource, and their gateway agents created 1:1, this creates a single point of failure within each replica.

This model is shown in the following example Kubernetes cluster using an external gateway agent:

Figure 1. External gateway agents

Although this model generally provides internal and external connectivity, it doesn’t promote the goal of high availability. However, horizontally autoscaling your gateway agents allows your cluster to dynamically handle workloads or the loss of a gateway agent. CloudBees CD/RO provides this option for horizontal pod autoscaling (HPA) with HPA gateway agents.

By default, the CloudBees CD/RO server does not include HPA gateway agents. You must manually configure gateway agent autoscaling.

Configuring HPA gateway agents

Using HPA gateway agents allows you to distribute the cluster workload over one or many agent replicas and provides availability if one fails. The following steps allow your HPA gateway agents to be registered as services, using a service name, instead of the resource name of individual pods.

The CloudBees CD/RO cloudbees-flow Helm chart is available in the public cloudbees-examples repository. CloudBees recommends you save this in a local myvaules.yaml to retain it within your environment.

In your CloudBees CD/RO cloudbees-flow Helm chart, add the following:

internalGatewayAgent:
    enabled: true
    autoscaling:
      enabled: true
      minReplicas: 1
      maxReplicas: 2
      targetCPUUtilizationPercentage: 80
      targetMemoryUtilizationPercentage: 80

# cloudbees-flow-agent chart configurations used for creating the
# external agent for the gateway
externalGatewayAgent:
    enabled: true
    autoscaling:
      enabled: true
      minReplicas: 1
      maxReplicas: 2
      targetCPUUtilizationPercentage: 80
      targetMemoryUtilizationPercentage: 80▼

For internalGatewayAgent, configure the following for your cluster:
1. minReplicas
2. maxReplicas
3. targetCPUUtilizationPercentage
4. targetMemoryUtilizationPercentage
  
  For HPA gateway agents to work, internalGatewayAgent.enabled and internalGatewayAgent.autoscaling.enabled must be set to true.
For externalGatewayAgent, configure the following for your cluster:
1. minReplicas
2. maxReplicas
3. targetCPUUtilizationPercentage
4. targetMemoryUtilizationPercentage
  
  For HPA gateway agents to work, externalGatewayAgent.enabled and externalGatewayAgent.autoscaling.enabled must be set to true.

Autoscaling non-gateway agents

CloudBees CD/RO does not support horizontal autoscaling of non-gateway agents. Attempts to follow these instructions for non-gateway agents will result in an error message for an invalid configuration.