Retry Strategies

Introduction

Jobs fail — networks drop, APIs rate-limit, databases lock. Active Job provides retry_on and discard_on to handle failures gracefully with configurable backoff strategies.

Key Concepts

• retry_on: Rescues a specific exception and re-enqueues after a wait period.
• discard_on: Rescues an exception and silently discards the job.
• Exponential Backoff: Retry wait times increase with each attempt.

Real World Context

A payment API job might fail from a temporary network issue — retrying in 30 seconds will likely succeed. But a job failing due to a deleted user should not retry.

Deep Dive

ruby
class ApiSyncJob < ApplicationJob
  retry_on StandardError, wait: :polynomially_longer, attempts: 3
  retry_on Timeout::Error, wait: 5.seconds, attempts: 5
  retry_on RateLimitError, wait: 1.minute, attempts: 10
  discard_on ActiveRecord::RecordNotFound
  discard_on ArgumentError

  def perform(record_id)
    record = Record.find(record_id)
    ExternalApi.sync(record)
  end
end

Custom Backoff with Jitter

ruby
class ResilientJob < ApplicationJob
  retry_on ApiError, wait: ->(executions) {
    (executions ** 2) + rand(30)
  }, attempts: 5
end

Common Pitfalls

1. Retrying non-transient errors — Retrying invalid input wastes resources. Use discard_on.
2. Not adding jitter — Simultaneous retries create storms. Add randomness.

Best Practices

1. Be specific with error classes — Don't rescue StandardError when you mean Timeout::Error.
2. Set appropriate attempt limits — 5 attempts covers most transient failures.

Summary

• Use retry_on for transient errors, discard_on for permanent ones.
• wait: :polynomially_longer provides increasing backoff.
• Add jitter to prevent retry storms.
• Be specific about which exceptions to handle.

class PaymentSyncJob < ApplicationJob
  retry_on PaymentGateway::TimeoutError, wait: :polynomially_longer, attempts: 5
  retry_on PaymentGateway::RateLimitError, wait: 1.minute, attempts: 10
  discard_on PaymentGateway::InvalidCardError

  def perform(payment_id)
    payment = Payment.find(payment_id)
    PaymentGateway.sync(payment)
  end
end