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

🚀 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

🚀 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.

🚀 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 output the imports folder in src/imports

  ⚡ $ 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

  ⚡ $ tree src/imports/
  src/imports/
  └── keda.sh.ts

  0 directories, 1 file

🚀 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

1. 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 nodes, join node to cluster and Pod ready (about 2-3mins) so we use cron to pre-scale workers

2. 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

3. 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 secret airflow-secret within the airflow namespace

    const 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.

🚀 Build keda scaledobjects from code

• Source code:

  ⚡ $ tree src/
  src/
  ├── imports
  │   └── keda.sh.ts
  ├── keda-airflow.ts
  └── main.ts

  1 directory, 3 files

• Build resource

  ⚡ $ npx projen build
  👾 build » default | ts-node --project tsconfig.dev.json .projenrc.ts
  👾 build » compile | tsc --build
  👾 build » post-compile » synth | cdk8s synth
  No manifests synthesized
  👾 build » 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 |
  ----------|---------|----------|---------|---------|-------------------
  👾 build » test » eslint | eslint --ext .ts,.tsx --fix --no-error-on-unmatched-pattern src test build-tools projenrc .projenrc.ts

• Manifest yaml file

  ⚡ $ tree dist/
  dist/
  └── keda
      └── airflow-keda-so.yaml

  1 directory, 1 file

🚀 Apply and test

• Apply manifest and check result

  # k apply -f dist/keda/airflow-keda-so.yaml

  # 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

🚀 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.

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