This document discusses using external scalers with KEDA (Kubernetes Event-driven Autoscaling) to allow KEDA to interact with systems outside the cluster to drive application scaling needs in a more customized way. It describes using gRPC to connect an external metrics adapter to KEDA's controller and provides an example demo of scaling applications based on messages in an ActiveMQ Artemis broker deployed outside the cluster. Relevant references are also included.

1. External scalers with KEDA

2. 2
Who me?
Baltazar Chua
Technical Architect
at
Credit Agricole CIB Singapore
https://github.com/balchua
www.linkedin.com/in/baltazar-chua
Avid fan of open source systems.
Sucker for cool tech.
Java guy by trade.
Go lang enthusiast.
Open source contributor
balchua@yahoo.com

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What is KEDA?
Kubernetes Event-driven Autoscaling
Architecture

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Available Scalers
Cloudeye
Liiklus
https://github.com/bsideup/liiklus

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KEDA in-tree scalers

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External Scalers
● Allows KEDA to interact with
external system to drive
application scaling needs.
● Out of tree scalers.
● Don’t need to change KEDA source to
add your scaler.
● Can we tailored to your specific
organization needs.

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External Scaler
Metrics
adapter
Controller Scaler
Custom
scaler
gRPC Event
Source /
Broker

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gRPC
● A high-performance, open source universal
RPC framework
● Can run in any environment
● Support for load balancing, tracing, health
check
● Available in multiple languages
● Uses Protocol Buffers
● HTTP/2
● Supports unary, client streaming, server
streaming and bi-directional streaming

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gRPC proto definitions
service ExternalScaler {
rpc New(NewRequest) returns (google.protobuf.Empty) {}
rpc IsActive(ScaledObjectRef) returns (IsActiveResponse) {}
rpc GetMetricSpec(ScaledObjectRef) returns (GetMetricSpecResponse) {}
rpc GetMetrics(GetMetricsRequest) returns (GetMetricsResponse) {}
rpc Close(ScaledObjectRef) returns (google.protobuf.Empty) {}
}
message ScaledObjectRef { string name = 1; string namespace = 2;}
message NewRequest { ScaledObjectRef scaledObjectRef = 1; map<string,
string> metadata = 2;}
message IsActiveResponse { bool result = 1;}
message GetMetricSpecResponse { repeated MetricSpec metricSpecs = 1;}
message MetricSpec { string metricName = 1; int64 targetSize = 2;}
message GetMetricsRequest { ScaledObjectRef scaledObjectRef = 1;
string metricName = 2;}
message GetMetricsResponse { repeated MetricValue metricValues = 1;}
message MetricValue { string metricName = 1; int64 metricValue = 2;}

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DEMO – External Scaling with KEDA and ActiveMQ
Artemis
Metrics
adapter
Controller Scaler
Management
endpoint
Consumer
pod
Consumer
pod
scale
Consumer
deploy
Consumer
pod
Producer
Kubernetes Cluster
Artemis
Metrics
Provider
pod

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References
●
The source codes - https://github.com/balchua/artemis-ext-scaler
●
Keda - https://keda.sh/
●
ActiveMQ Artemis - https://activemq.apache.org/components/artemis/
●
Skaffold - https://skaffold.dev/
●
Kubernetes HPA -
https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/
●
MicroK8s - https://microk8s.io/