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Retry Flow

The Retry Flow automatically handles retries for failed API requests based on configurable criteria, such as status codes and retry strategies. It is designed to enhance API reliability by managing temporary failures without requiring client-side retry logic.

Flow Diagram

Scenarios​

  1. Handling Temporary API Failures: Automatically retry failed requests, reducing manual error handling.
  2. Improving Reliability: Manage network issues and server downtime with exponential backoff retries.
  3. Enhanced Monitoring: Track retry attempts, cooldowns, and related performance metrics.

Flow Configuration Template​

/etc/lunar-proxy/flows/flow.yaml
name: RetryFlow

filter:
  url: "api.com/resource/{id}"  # Target URL pattern for retry logic
processors:
  FilterProcessor:
    processor: Filter
    parameters:
      - key: status_code_range
        value: 400-500 # Set the range if status code to trigger the filter.
    metrics:
      enabled: true
      labels:
        - flow_name
        - processor_key
        - http_method
        - host
        - status_code
        - consumer_tag
  RetryProcessor:
    processor: Retry  # Specifies the Retry processor
    parameters:
      - key: attempts
        value: 3  # Maximum number of retry attempts
      - key: cooldown_between_attempts_seconds
        value: 2  # Initial cooldown time before the first retry (in seconds)
      - key: cooldown_multiplier
        value: 2  # Multiplier for exponential backoff
      - key: maximum_cooldown_seconds
        value: 3600 # Maximum time to wait between each retry (in seconds)
    metrics:
      enabled: true  # Enables metric collection
      labels:
        - flow_name  # Include the flow name as a label
        - processor_key  # Include the processor key as a label
        - http_method  # Include the HTTP method (GET, POST, etc.)
        - url  # Include the URL of the request
        - status_code  # Include the HTTP status code of the response
flow:
  request:
    - from:
        stream:
          name: globalStream  
          at: start
      to:
        stream:
          name: globalStream
          at: end
  response:
    - from:
        stream:
          name: globalStream # Use the global stream for capturing requests
          at: start
      to:
        processor:
          name: FilterProcessor 
    - from: 
        processor:
          name: FilterProcessor
          condition: miss
      to:
        stream:
          name: globalStream
          at: end
    - from:
        processor:
          name: FilterProcessor
          condition: hit # In case the status code match the configured range
      to:
        processor:
          name: RetryProcessor # Route the request to the RetryProcessor
    - from:
        processor:
          name: RetryProcessor
          condition: retry
      to:
        stream:
          name: globalStream
          at: end
    - from:
        processor:
          name: RetryProcessor
          condition: failed
      to:
        stream:
          name: globalStream
          at: end

Flow Example

This is an example of a fully configured Retry Flow that retries failed API requests based on status codes, with exponential backoff.

/etc/lunar-proxy/flows/flow.yaml
name: RetryFlow

filter:
  url: "api.com/resource/{id}"
processors:
  RetryProcessor:
    processor: Retry
    parameters:
      - key: attempts
        value: 5
      - key: cooldown_between_attempts_seconds
        value: 5
      - key: cooldown_multiplier
        value: 1.5
      - key: maximum_cooldown_seconds
        value: 3600
  FilterProcessor:
    processor: Filter
    parameters:
      - key: status_code_range
        value: 400-500
flow:
  request:
    - from:
        stream:
          name: globalStream
          at: start
      to:
        stream:
          name: globalStream
          at: end
  response:
    - from:
        stream:
          name: globalStream
          at: start
      to:
        processor:
          name: FilterProcessor
    - from: 
        processor:
          name: FilterProcessor
          condition: miss
      to:
        stream:
          name: globalStream
          at: end
    - from:
        processor:
          name: FilterProcessor
          condition: hit
      to:
        processor:
          name: RetryProcessor
    - from:
        processor:
          name: RetryProcessor
          condition: retry
      to:
        stream:
          name: globalStream
          at: end
    - from:
        processor:
          name: RetryProcessor
          condition: failed
      to:
        stream:
          name: globalStream
          at: end

Flow Components​

Troubleshooting​

  1. Retries Not Triggering:
    • Verify that status_code_range is correctly configured.
    • Ensure the API response status code falls within the specified range.
  2. Excessive Retry Attempts:
    • Check the attempts parameter and reduce it if necessary.
    • Adjust the cooldown_multiplier to increase wait times between retries.
    • Make sure that in case of long cooldown the value of LUNAR_RETRY_REQUEST_TIMEOUT_SEC is also increased. the default is 100