feat: add disableCache flag to ApiServerSource adapter

[Ankitsinghsisodya]

Fixes #8642

Problem

ApiServerSource watching 5 resources across 1000+ namespaces triggers ~5000 LIST calls on startup, causing client-side throttling:

Waited for 17m12s due to client-side throttling... GET .../taskruns?resourceVersion=0

Root cause: the adapter's reflector always does LIST+WATCH per namespace per resource. With 1000+ namespaces that's O(resources × namespaces) LIST requests.

Solution

Add a disableCache field to ApiServerSourceSpec. When true, the adapter skips the initial LIST call entirely and only opens Watch connections — reducing startup API calls from ~5000 to ~5 (one Watch per resource type).

Semantic trade-off: pre-existing objects do not emit events on adapter startup. Only events for objects created/modified/deleted after the adapter starts are emitted.

Changes

File	Change
pkg/apis/sources/v1/apiserver_types.go	DisableCache bool field on ApiServerSourceSpec
pkg/adapter/apiserver/config.go	DisableCache bool in adapter Config
pkg/adapter/apiserver/adapter.go	startWatchOnly() — Watch-only loop with reconnect; branch before FailFast/Resilient
pkg/reconciler/apiserversource/apiserversource.go	Pass src.Spec.DisableCache to adapter args
pkg/reconciler/apiserversource/resources/receive_adapter.go	DisableCache in ReceiveAdapterArgs, serialized into K_SOURCE_CONFIG
config/core/resources/apiserversource.yaml	disableCache: boolean in CRD openAPIV3Schema
*_test.go	Unit tests covering no-cache start path and verifying no LIST call is made

Usage

apiVersion: sources.knative.dev/v1
kind: ApiServerSource
metadata:
  name: tekton-taskrun-source
spec:
  disableCache: true
  resources:
    - apiVersion: tekton.dev/v1
      kind: TaskRun
  namespaceSelector: {}
  sink:
    ref:
      apiVersion: v1
      kind: Service
      name: my-sink

Test plan

• go test ./pkg/adapter/apiserver/... — passes, includes TestAdapter_DisableCache and TestAdapter_DisableCacheSkipsList
• go test ./pkg/reconciler/apiserversource/... — passes, includes TestMakeReceiveAdapterWithDisableCache
• Integration test in a cluster with many namespaces (reproducer pending from issue author)

[knative-prow]

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This pull-request has been approved by: Ankitsinghsisodya
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[knative-prow]

Hi @Ankitsinghsisodya. Thanks for your PR.

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[Copilot]

Pull request overview

Adds an opt-in disableCache flag to ApiServerSource so the adapter can skip the initial LIST phase and rely on WATCH-only startup, reducing API server load in large clusters (e.g., many namespaces).

Changes:

• Introduces spec.disableCache (API + CRD schema) and propagates it through reconciler/receive-adapter config into the adapter.
• Implements a watch-only startup path (startWatchOnly) in the apiserver adapter when DisableCache=true.
• Adds unit tests for config serialization and to verify the no-cache path does not perform LIST calls; bumps Slack notify GitHub Action versions in workflows.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pkg/apis/sources/v1/apiserver_types.go	Adds DisableCache field to ApiServerSourceSpec with documentation.
config/core/resources/apiserversource.yaml	Exposes disableCache in the CRD OpenAPI schema.
pkg/reconciler/apiserversource/apiserversource.go	Passes src.Spec.DisableCache into receive-adapter args.
pkg/reconciler/apiserversource/resources/receive_adapter.go	Adds DisableCache to adapter args and serializes into K_SOURCE_CONFIG.
pkg/reconciler/apiserversource/resources/receive_adapter_test.go	Tests K_SOURCE_CONFIG serialization includes/omits disableCache.
pkg/adapter/apiserver/config.go	Adds DisableCache to adapter runtime config.
pkg/adapter/apiserver/adapter.go	Adds startWatchOnly and routes to it when DisableCache=true.
pkg/adapter/apiserver/adapter_test.go	Adds adapter unit tests for no-cache startup and LIST-skipping.
.github/workflows/weekly-office-hours-slack-reminder.yaml	Updates Slack notify action version.
.github/workflows/kind-e2e.yaml	Updates Slack notify action version.

---

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[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 60 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.51%. Comparing base (d5f437f) to head (d8067fa).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/adapter/apiserver/adapter.go	53.12%	52 Missing and 8 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #9036    +/-   ##
========================================
  Coverage   50.51%   50.51%            
========================================
  Files         409      409            
  Lines       27505    27635   +130     
========================================
+ Hits        13893    13961    +68     
- Misses      12752    12803    +51     
- Partials      860      871    +11     

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[Ankitsinghsisodya]

@creydr can you please run /retest? I think these these test cases are flaky.

[creydr]

/ok-to-test

[Ankitsinghsisodya]

@creydr can you we again /restest the failed test cases.

[creydr]

/retest