Job retries and error handling in Ruby on Rails

Introduction

Job retries help your app try again if something goes wrong. Error handling lets you manage problems smoothly without crashing.

When sending emails that might fail due to network issues.

When processing payments that could time out or fail temporarily.

When calling external APIs that might be down or slow.

When running background tasks that depend on resources that may be temporarily unavailable.

Syntax

Ruby on Rails

class MyJob < ApplicationJob
  retry_on SomeError, wait: 5.seconds, attempts: 3

  def perform(*args)
    # job code here
  rescue AnotherError => e
    # handle specific error
  end
end

retry_on tells Rails to retry the job if the specified error happens.

You can set how long to wait between retries and how many times to try.

Examples

This retries sending an email up to 5 times if there is a network timeout.

Ruby on Rails

class EmailJob < ApplicationJob
  retry_on Net::OpenTimeout, wait: 10.seconds, attempts: 5

  def perform(user_id)
    user = User.find(user_id)
    UserMailer.welcome_email(user).deliver_now
  end
end

This retries with longer waits each time, up to 4 tries, for any standard error.

Ruby on Rails

class DataImportJob < ApplicationJob
  retry_on StandardError, wait: :exponentially_longer, attempts: 4

  def perform(file_path)
    # import logic
  end
end

This discards the job immediately if the record is not found, no retries.

Ruby on Rails

class CleanupJob < ApplicationJob
  discard_on ActiveRecord::RecordNotFound

  def perform(record_id)
    record = Record.find(record_id)
    record.cleanup
  end
end

Sample Program

This job is configured to retry_on RuntimeError with wait: 3.seconds and attempts: 2. Directly calling perform bypasses the ActiveJob queue and retry logic. In a real application, enqueue the job using perform_later(true) to see the retry behavior in action. The sample shows a single failure and a success case.

Ruby on Rails

class RetryExampleJob < ApplicationJob
  retry_on RuntimeError, wait: 3.seconds, attempts: 2

  def perform(should_fail)
    puts "Job started"
    if should_fail
      puts "Simulating failure"
      raise RuntimeError, "Something went wrong"
    end
    puts "Job succeeded"
  end
end

# Simulate running the job with failure
job = RetryExampleJob.new
begin
  job.perform(true)
rescue RuntimeError => e
  puts "Job failed: #{e.message}"
end

# Run the job without failure
job.perform(false)

Important Notes

Time complexity: Depends on job duration and retry count.

Space complexity: Minimal, just job data stored between retries.

Common mistake: Not handling specific errors, causing infinite retries.

Use retries for temporary errors; use discard_on for permanent failures.

Summary

Job retries let your app try again if a job fails temporarily.

Error handling helps manage problems without crashing your app.

Use retry_on and discard_on to control retry behavior in Rails jobs.

Practice

1. What does the retry_on method do in a Rails Active Job?

easy

A. It retries the job automatically if a specified error occurs.

B. It discards the job immediately without retrying.

C. It schedules the job to run only once without retries.

D. It logs the error but does not retry the job.

Solution

1. Step 1: Understand retry_on purpose

   The retry_on method tells Rails to retry a job if a certain error happens during execution.

2. Step 2: Compare with other options

   Unlike discard_on, which stops retries, retry_on allows automatic retrying.

3. Final Answer:

   It retries the job automatically if a specified error occurs. -> Option A

4. Quick Check:

   retry_on = automatic retry [OK]

Hint: Remember: retry_on means try again on error [OK]

Common Mistakes:

• Confusing retry_on with discard_on
• Thinking retry_on discards the job
• Assuming retry_on logs errors only

2. Which of the following is the correct syntax to retry a job on ActiveRecord::Deadlocked error with 3 attempts in Rails?

easy

A. retry_on(ActiveRecord::Deadlocked, attempts: 3)

B. retry_on ActiveRecord::Deadlocked attempts=3

C. retry_on ActiveRecord::Deadlocked attempts: 3

D. retry_on(ActiveRecord::Deadlocked attempts: 3)

Solution

1. Step 1: Recall method call syntax in Ruby

   Methods with arguments and options require parentheses for clarity, especially with keyword arguments.

2. Step 2: Check each option's syntax

   retry_on(ActiveRecord::Deadlocked, attempts: 3) uses parentheses and correct keyword argument syntax: retry_on(ActiveRecord::Deadlocked, attempts: 3).

3. Final Answer:

   retry_on(ActiveRecord::Deadlocked, attempts: 3) -> Option A

4. Quick Check:

   Correct method call syntax = retry_on(ActiveRecord::Deadlocked, attempts: 3) [OK]

Hint: Use parentheses with keyword args for retry_on [OK]

Common Mistakes:

• Omitting parentheses with keyword arguments
• Using equal sign instead of colon for options
• Missing commas between arguments

3. Given this job code:

class MyJob < ApplicationJob
  retry_on StandardError, attempts: 2

  def perform
    raise StandardError, "fail"
  end
end

MyJob.perform_now

What happens when MyJob.perform_now is called?

medium

A. The job silently discards the error and finishes.

B. The job raises StandardError once and stops.

C. The job retries twice after failures, then raises error.

D. The job retries once after the first failure, then raises error.

Solution

1. Step 1: Understand retry_on with attempts: 2

   It means the job will try up to 2 times total (1 initial + 1 retry) before giving up.

2. Step 2: Analyze job behavior

   The job raises StandardError every time. It runs once, fails, retries once, then fails again and raises error.

3. Final Answer:

   The job retries once after the first failure, then raises error. -> Option D

4. Quick Check:

   attempts: 2 means 1 retry [OK]

Hint: attempts count includes first try, so retries = attempts - 1 [OK]

Common Mistakes:

• Thinking attempts means retries count
• Assuming job discards error automatically
• Believing job retries infinitely

4. Identify the error in this job code snippet:

class ExampleJob < ApplicationJob
  retry_on(StandardError, attempts: 3)

  def perform
    # job logic
  end
end

medium

A. The retry_on method should be called inside perform method.

B. The retry_on method should not have parentheses.

C. The retry_on method is correctly used; no error.

D. The retry_on method should be declared with a block.

Solution

1. Step 1: Check retry_on usage location

   retry_on is a class-level method and should be declared outside perform method, as shown.

2. Step 2: Verify syntax correctness

   Using parentheses with arguments is valid Ruby syntax here.

3. Final Answer:

   The retry_on method is correctly used; no error. -> Option C

4. Quick Check:

   retry_on class method syntax is correct [OK]

Hint: retry_on is a class method, not inside perform [OK]

Common Mistakes:

• Placing retry_on inside perform method
• Thinking parentheses are disallowed
• Expecting retry_on to require a block

5. You want a job to retry up to 5 times on Net::OpenTimeout errors but discard immediately on ArgumentError. Which code correctly implements this behavior?

hard

A. class NetworkJob < ApplicationJob
discard_on Net::OpenTimeout
retry_on ArgumentError, attempts: 5

def perform
# network call
end
end

B. class NetworkJob < ApplicationJob
retry_on Net::OpenTimeout, attempts: 5
discard_on ArgumentError

def perform
# network call
end
end

C. class NetworkJob < ApplicationJob
retry_on Net::OpenTimeout
retry_on ArgumentError, attempts: 5

def perform
# network call
end
end

D. class NetworkJob < ApplicationJob
discard_on Net::OpenTimeout, attempts: 5
discard_on ArgumentError

def perform
# network call
end
end

Solution

1. Step 1: Understand retry_on and discard_on roles

   retry_on retries job on specified error; discard_on stops retries and discards job immediately.

2. Step 2: Match errors to correct methods

   Net::OpenTimeout should retry up to 5 times, so use retry_on with attempts: 5. ArgumentError should discard immediately, so use discard_on.

3. Final Answer:

   Code with retry_on Net::OpenTimeout, attempts: 5 and discard_on ArgumentError -> Option B

4. Quick Check:

   retry_on for retry, discard_on for discard [OK]

Hint: retry_on = retry; discard_on = stop and discard [OK]

Common Mistakes:

• Swapping retry_on and discard_on for errors
• Missing attempts option for retry_on
• Using discard_on with attempts option