General

What is KEDA and why is it useful?

KEDA stands for Kubernetes-based Event Driven Auto-Scaler. It is built to be able to activate a Kubernetes deployment (i.e. no pods to a single pod) and subsequently to more pods based on events from various event sources.

What are the prerequisites for using KEDA?

KEDA is designed to be run on any Kubernetes cluster. It uses a CRD (custom resource definition) and the Kubernetes metric server so you will have to use a Kubernetes version which supports these. Any Kubernetes cluster >= 1.16.0 has been tested and should work.

Can KEDA be used in production?

Yes! KEDA v2.0 is suited for production workloads, but we still support v1.5 if you are running that as well..

What does it cost?

There is no charge for using KEDA itself, we just ask people to become a listed user when possible.

Best Practices

Using multiple triggers for the same scale target

KEDA allows you to use multiple triggers as part of the same ScaledObject or ScaledJob.

By doing this, your autoscaling becomes better:

  • All your autoscaling rules are in one place
  • You will not have multiple ScaledObject's or ScaledJob's interferring with each other

KEDA will start scaling as soon as when one of the triggers meets the criteria. Horizontal Pod Autoscaler (HPA) will calculate metrics for every scaler and use the highest desired replica count to scale the workload to.

Don’t combine ScaledObject with Horizontal Pod Autoscaler (HPA)

We recommend not to combine using KEDA’s ScaledObject with a Horizontal Pod Autoscaler (HPA) to scale the same workload.

They will compete with each other resulting given KEDA uses Horizontal Pod Autoscaler (HPA) under the hood and will result in odd scaling behavior.

If you are using a Horizontal Pod Autoscaler (HPA) to scale on CPU and/or memory, we recommend using the CPU scaler & Memory scaler scalers instead.

Features

Can I scale HTTP workloads with KEDA and Kubernetes?

KEDA will scale a container using metrics from a scaler, but unfortunately there is no scaler today for HTTP workloads out-of-the-box.

We do, however, provide some alternative approaches:

Is short polling intervals a problem?

Polling interval really only impacts the time-to-activation (scaling from 0 to 1) but once scaled to one it’s really up to the HPA (horizontal pod autoscaler) which polls KEDA.

How do I run KEDA with readOnlyRootFilesystem=true?

By default you can’t run KEDA with readOnlyRootFilesystem=true because Metrics adapter generates self-signed certificates during deployment and stores them on the root file system. To overcome this, you can create a secret/configmap with a valid CA, cert and key and then mount it to the Metrics Deployment. To use your certificate, you need to reference it in the container args section, e.g.:

args:
  - '--client-ca-file=/cabundle/service-ca.crt'
  - '--tls-cert-file=/certs/tls.crt'
  - '--tls-private-key-file=/certs/tls.key'

Kubernetes

What does the target metric value in the Horizontal Pod Autoscaler (HPA) represent?

The target metric value is used by the Horizontal Pod Autoscaler (HPA) to make scaling decisions.

The current target value on the Horizontal Pod Autoscaler (HPA) often does not match with the metrics on the system you are scaling on. This is because of how the Horizontal Pod Autoscaler’s (HPA) scaling algorithm works.

Community

How can I get involved?

There are several ways to get involved.

  • Pick up an issue to work on. A good place to start might be issues which are marked as Good First Issue or Help Wanted
  • We are always looking to add more scalers.
  • We are always looking for more samples, documentation, etc.
  • Please join us in our weekly standup.

Where can I get to the code for the Scalers?

All scalers have their code here.

Integrations

Microsoft Azure

Does KEDA depend on any Azure service?

No, KEDA only takes a dependency on standard Kubernetes constructs and can run on any Kubernetes cluster whether in OpenShift, AKS, GKE, EKS or your own infrastructure.

Does KEDA only work with Azure Functions?

No, KEDA can scale up/down any container that you specify in your deployment. There has been work done in the Azure Functions tooling to make it easy to scale an Azure Function container.

Why should we use KEDA if we are already using Azure Functions in Azure?

There are a few reasons for this:

  • Run functions on-premises (potentially in something like an ‘intelligent edge’ architecture)
  • Run functions alongside other Kubernetes apps (maybe in a restricted network, app mesh, custom environment, etc.)
  • Run functions outside of Azure (no vendor lock-in)
  • Specific need for more control (GPU enabled compute clusters, policies, etc.)