feat: add redis fallback mechanism #21043

[NeatGuyCoding]

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3. Use the correct syntax to link this PR: Fixes #21043.

Summary

This PR introduces a Redis fallback mechanism to improve the resilience of the Dify application when Redis operations fail. The implementation includes:

• New redis_fallback decorator: A decorator function that gracefully handles Redis operation exceptions and returns configurable default values when Redis is unavailable
• Enhanced error handling: Applied the fallback mechanism to critical account service methods that depend on Redis for rate limiting functionality
• Logging integration: Added proper logging to track Redis operation failures for monitoring and debugging purposes

Key Changes:

• Added redis_fallback decorator in ext_redis.py to handle RedisError exceptions
• Applied the decorator to rate limiting methods in account_service.py:
  • add_login_error_rate_limit()
  • is_login_error_rate_limit()
  • reset_login_error_rate_limit()
  • add_forgot_password_error_rate_limit()
• Included comprehensive unit tests to ensure the fallback mechanism works correctly

This enhancement ensures that authentication and rate limiting features continue to function (with degraded capability) even when Redis is temporarily unavailable, preventing complete service disruption.

Fix #21043

Screenshots

Before	After
Redis failures would cause unhandled exceptions and potential service disruption	Redis failures are gracefully handled with fallback behavior and proper logging

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[Copilot]

Pull Request Overview

This PR adds a Redis fallback capability to prevent service disruptions when Redis is unavailable by introducing a decorator and applying it to rate‐limiting methods, along with tests for the decorator.

• Introduces redis_fallback decorator in ext_redis.py for handling RedisError with configurable defaults and logging
• Applies the decorator to key rate‐limiting methods in account_service.py
• Adds unit tests for the fallback decorator behavior in test_redis.py

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
api/extensions/ext_redis.py	Adds redis_fallback decorator with logging of failures
api/services/account_service.py	Decorates rate‐limit methods with Redis fallback logic
api/tests/unit_tests/extensions/test_redis.py	Introduces tests to validate the decorator functionality

Comments suppressed due to low confidence (1)

api/services/account_service.py:498

• Add unit tests for this decorated method to confirm that it returns None and logs appropriately when Redis operations throw an error.

    @redis_fallback(default_return=None)