WatchedSetting based refresh

[linglingye001]

Overall
The refresh mechanism is designed around these key components:

• watchedSettings: The specific settings to monitor for changes
• sentinalETags: Stores ETags for tracked settings to detect changes
• kvRefreshTimer: Controls refresh intervals using a timer
• refreshKeyValues: Core logic that handles checking and refreshing
• watchedSettingClient: Checks if ETags have changed using Azure's API

Refresh Control Flow
The refresh process follows this logical flow:

• Initialization (during Load):

  • Validates refresh configuration (interval and watched settings)
  • Sets up the refresh timer with configured interval
  • Loads initial configuration and ETags for watched settings
  • Refresh Invocation (in Refresh method):

• Checks if refresh is enabled

  • Uses mutex to prevent concurrent refreshes
  • Checks if it's time to refresh (using refresh timer)
  • Calls refreshKeyValues to check and reload if needed
  • Executes success callbacks only if configuration actually changed
  • Change Detection (in refreshKeyValues):

• Creates/uses a monitor to check ETags

  • Uses Azure's API with OnlyIfChanged flag for efficient checking
  • Only proceeds with reloading if ETags have changed
  • Resets timer if no changes detected (early return)
  • Configuration Reloading (if changes detected):

• Reloads all key-values concurrently using errgroup

  • Reloads watched settings to get new ETags
  • Updates the monitor with new ETags
  • Resets the timer only after successful reload
  • Returns true to indicate successful refresh

• Error Handling:

  • Does not reset the timer if reload fails
  • Returns specific error messages for different failure points
  • Maintains refresh status to avoid duplicate refreshes

[Copilot]

Pull Request Overview

This PR implements a refresh mechanism based on watched settings, adding validation, monitoring, and concurrent reloading of configuration when changes occur.

• Added validation and normalization for refresh options and watched settings.
• Introduced a dedicated refresh timer and corresponding client logic for Azure App Configuration.
• Expanded test coverage to validate various refresh scenarios.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
utils.go	Adds validations for refresh options including interval and watched settings.
settings_client.go	Introduces watchedSettingClient with error handling and ETag check logic.
refresh_test.go	Provides comprehensive tests for refresh functionality and configuration updates.
options.go	Defines new refresh options and watched settings structures.
internal/refreshtimer/refresh_timer.go	Implements a refresh timer to control refresh intervals.
constants.go	Adds minimal refresh interval constant.
azureappconfiguration.go	Implements refresh logic including mutual exclusion, reloading key-values and watched settings.

[RichardChen820]

I guess it can be removed now?

[linglingye001]

Yes, it should be removed

[RichardChen820]

nit:

if err := azappcfg.load(ctx); err != nil {
		return nil, err
	} 
	
	azappcfg.tracingOptions.InitialLoadFinished = true