Keda ScaledObject As Code Using CDK8S
Abstract
- keda is Kubernetes Event-driven Autoscaling and it's been used wisely now. In this blog, it provides the way to create Keda scaledobject CRD as code using CDK8S typescript.
- With importing Keda CRDs and using CDK8S you can create Keda scaledobjects using your familiar programming languages such as typescript as scale.
Table Of Contents
- Pre-requisite
- Overview of Keda
- Import Keda CRDs
- Write code
- Build keda scaledobjects from code
- Apply and test
- Conclusion
π Pre-requisite
- Install typescript, node, and cdk8s as well as projen (optional) which is a tool of managing project configuration as code.
- Getting started with cdk8s
π Overview of Keda
- KEDA works alongside standard Kubernetes components like the Horizontal Pod Autoscaler and can extend functionality without overwriting or duplication.
- KEDA supports multiple triggers within an Scaledobject. Each trigger is exposed split as a metric and the HPA Controller does a MAX between all the metrics.
π Import Keda CRDs
-
Keda does not provide its CRDs separately so we can found the manifest in GH release section. Here I import the current latest version of keda v2.8.0 and out the
imports
folder insrc/imports
β‘ $ cdk8s import https://github.com/kedacore/keda/releases/download/v2.8.0/keda-2.8.0.yaml --output src/imports/ ------------------------------------------------------------------------------------------------ A new version 2.0.88 of cdk8s-cli is available (current 2.0.13). Run "npm install -g cdk8s-cli" to install the latest version on your system. For additional installation methods, see https://cdk8s.io/docs/latest/getting-started ------------------------------------------------------------------------------------------------ Importing resources, this may take a few moments... keda.sh keda.sh/clustertriggerauthentication keda.sh/scaledjob keda.sh/scaledobject keda.sh/triggerauthentication
-
Import result
β‘ $ tree src/imports/ src/imports/ βββ keda.sh.ts 0 directories, 1 file
π Write code
-
Overview of keda scaledObjects in this post
-
It's much more convinient to use visual code writing KEDA scaledobject in typescript language. We can read the document and find all references of construct, objects and properties of KEDA CRDs
-
This blog provides the usecase of creating scaledObject (SO) for Apache airflow worker component. It contains 3 triggers (Scalers) in the SO
-
Cron - Scale applications based on a cron schedule. Airflow server scheduled pipelines and worker components are scaled out at that time, but it takes time to start node, join node to cluster and Pod ready (about 2-3mins) so we use cron to pre-scale workers
-
PostgreSQL - Scale applications based on a PostgreSQL query.
- This scaler bases on the output of query command to scaleout works, here we count the number of running/queued airflow task instances belongs to scheduled pipeline (eg. running reports). Divide the count number to Airflow worker concurrency (eg. 16 as default)
targetQueryValue: '1.5'
- The result of above calculation divide to this target value to decide how many pods will be scaled out
- CPU - Scale applications based on cpu metrics
- This is optional as it ensure provisioning workers when CPU Utilization is higher than 80%
-
-
PostgreSQL Scaler requires
TriggerAuthentication
to provide password of airflow user in order to query the database. The credential is get from K8S secretairflow-secret
within theairflow
namespaceconst pgAuth = new TriggerAuthentication(this, 'KedaPostgresAuthentication', { metadata: { name: 'keda-airflow-postgresql-auth', namespace: 'airflow', }, spec: { secretTargetRef: [{ parameter: 'password', name: 'airflow-secret', key: 'postgresql-password', }], }, });
-
Some SO specs need to know
pollingInterval
: This is the interval to check each trigger on. By default KEDA will check each trigger source on every ScaledObject every 30 seconds. So to reduce the query connections/workload to airflow database we need to care this vaule.cooldownPeriod
: The period to wait after the last trigger reported active before scaling the resource back to 0.
π Build keda scaledobjects from code
-
Source code:
β‘ $ tree src/ src/ βββ imports β βββ keda.sh.ts βββ keda-airflow.ts βββ main.ts 1 directory, 3 files
-
Build resource
β‘ $ npx projen build πΎ build Β» default | ts-node --project tsconfig.dev.json .projenrc.ts πΎ build Β» compile | tsc --build πΎ build Β» post-compile Β» synth | cdk8s synth No manifests synthesized πΎ build Β» test | jest --passWithNoTests --all --updateSnapshot No tests found, exiting with code 0 ----------|---------|----------|---------|---------|------------------- File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s ----------|---------|----------|---------|---------|------------------- All files | 0 | 0 | 0 | 0 | ----------|---------|----------|---------|---------|------------------- πΎ build Β» test Β» eslint | eslint --ext .ts,.tsx --fix --no-error-on-unmatched-pattern src test build-tools projenrc .projenrc.ts
-
Manifest yaml file
β‘ $ tree dist/ dist/ βββ keda βββ airflow-keda-so.yaml 1 directory, 1 file
π Apply and test
- Apply manifest and check result
# k apply -f # k get so -n airflow NAME SCALETARGETKIND SCALETARGETNAME MIN MAX TRIGGERS AUTHENTICATION READY ACTIVE FALLBACK AGE airflow-worker-1 apps/v1.StatefulSet airflow-worker 2 12 cron keda-airflow-postgresql-auth True True False 2d21h # k get hpa -n airflow NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE keda-hpa-airflow-worker-1 StatefulSet/airflow-worker 500m/1 (avg), 500m/1 (avg) + 2 more... 2 12 2 2d21h
π Conclusion
- Within the Scaledobject class, you can jump to definition to understand the meaning of each properties and also know which required/optional attributes.
- We can create a custom construct and base on that to provision multiple KEDA scaledobjects with customize specs/meta such as min/max/desired replicas, triggers, trigger authentication, etc.