Version: 2019-05-29 (Current)

Idempotency

Safely retry API requests without creating duplicate charges, customers, or other resources. Learn how to use idempotency keys to build reliable payment integrations.

Overview

Network issues, timeouts, and server errors can cause API requests to fail or return unclear results. Idempotency allows you to safely retry requests without worrying about duplicate operations. By providing an Idempotency-Key header, Omise guarantees the same request will produce the same result, even if sent multiple times.

Quick Start

Add Idempotency-Key header to POST/PATCH requests
Use unique key per operation (UUID recommended)
Same key returns same result (cached for 24 hours)
Essential for charge creation and money operations
Prevents duplicate payments during network issues

What is Idempotency?

Idempotency means an operation can be performed multiple times with the same result. In payment processing, this is critical:

Without Idempotency

Send charge request → Network timeout
Did it succeed? Unknown. Retry?
Retry → Duplicate charge! Customer charged twice 💥

With Idempotency

Send charge with idempotency key → Network timeout
Retry with same key → Same result returned
No duplicate charge ✅

How Idempotency Works

You send a request with an Idempotency-Key header
Omise processes it and stores the result
If you retry with the same key within 24 hours:
- Omise returns the cached result
- No new operation is performed
- Same response status code and body

Example Flow

# First request (network timeout)
curl https://api.omise.co/charges \
  -X POST \
  -u skey_test_...: \
  -H "Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000" \
  -d "amount=100000" \
  -d "currency=thb" \
  -d "card=tokn_test_..."
# Response: (timeout - unclear if succeeded)

# Retry with same key
curl https://api.omise.co/charges \
  -X POST \
  -u skey_test_...: \
  -H "Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000" \
  -d "amount=100000" \
  -d "currency=thb" \
  -d "card=tokn_test_..."
# Response: Returns the original charge (not a new one)

When to Use Idempotency

Always Use For:

✅ Creating Charges

POST /charges

Most important - prevents duplicate payments

✅ Creating Customers

POST /customers

Prevents duplicate customer records

✅ Creating Refunds

POST /charges/:id/refunds

Prevents duplicate refunds

✅ Creating Transfers

POST /transfers

Prevents duplicate payouts

✅ Creating Recipients

POST /recipients

Prevents duplicate recipient records

✅ Any POST Request All POST requests that create resources should use idempotency keys

✅ PATCH Requests Updates can be retried safely with idempotency

Not Needed For:

❌ GET Requests Reading data is already idempotent (no side effects)

❌ DELETE Requests Deleting is naturally idempotent (deleting twice = same result)

Idempotency-Key Header

Header Format

Idempotency-Key: <unique-string>

Key Requirements

Requirement	Description
Format	Any string up to 255 characters
Uniqueness	Must be unique per operation
Characters	Alphanumeric and hyphens recommended
Case Sensitive	`key-1` ≠ `KEY-1`
Lifetime	Stored for 24 hours

Recommended: Use UUIDs

# UUIDv4 format (recommended)
Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000

Why UUIDs?

✅ Guaranteed uniqueness
✅ No collision risk
✅ Standard format
✅ Available in all languages

Implementation Examples

Ruby

require 'omise'
require 'securerandom'

Omise.api_key = ENV['OMISE_SECRET_KEY']

# Generate unique idempotency key
idempotency_key = SecureRandom.uuid

begin
  charge = Omise::Charge.create({
    amount: 100000,
    currency: 'thb',
    card: token
  }, {
    'Idempotency-Key' => idempotency_key
  })

  puts "Charge created: #{charge.id}"

rescue Omise::Error => e
  if e.http_status >= 500 || e.message.include?('timeout')
    # Safe to retry with same key
    charge = Omise::Charge.create({
      amount: 100000,
      currency: 'thb',
      card: token
    }, {
      'Idempotency-Key' => idempotency_key  # Same key!
    })
  else
    raise
  end
end

Python

import omise
import uuid

omise.api_secret = os.environ['OMISE_SECRET_KEY']

# Generate unique idempotency key
idempotency_key = str(uuid.uuid4())

try:
    charge = omise.Charge.create(
        amount=100000,
        currency='thb',
        card=token,
        headers={'Idempotency-Key': idempotency_key}
    )
    print(f"Charge created: {charge.id}")

except omise.errors.BaseError as e:
    if e.http_status >= 500:
        # Safe to retry with same key
        charge = omise.Charge.create(
            amount=100000,
            currency='thb',
            card=token,
            headers={'Idempotency-Key': idempotency_key}  # Same key!
        )
    else:
        raise

PHP

<?php
require_once 'vendor/autoload.php';

define('OMISE_SECRET_KEY', getenv('OMISE_SECRET_KEY'));

// Generate unique idempotency key
$idempotencyKey = sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
    mt_rand(0, 0xffff), mt_rand(0, 0xffff),
    mt_rand(0, 0xffff),
    mt_rand(0, 0x0fff) | 0x4000,
    mt_rand(0, 0x3fff) | 0x8000,
    mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
);

try {
    $charge = OmiseCharge::create([
        'amount' => 100000,
        'currency' => 'thb',
        'card' => $token
    ], [
        'Idempotency-Key' => $idempotencyKey
    ]);

    echo "Charge created: " . $charge['id'];

} catch (Exception $e) {
    if ($e->getCode() >= 500) {
        // Retry with same key
        $charge = OmiseCharge::create([
            'amount' => 100000,
            'currency' => 'thb',
            'card' => $token
        ], [
            'Idempotency-Key' => $idempotencyKey  // Same key!
        ]);
    } else {
        throw $e;
    }
}

Node.js

const omise = require('omise')({
  secretKey: process.env.OMISE_SECRET_KEY
});
const { v4: uuidv4 } = require('uuid');

async function createChargeWithRetry(chargeData, maxRetries = 3) {
  // Generate unique idempotency key
  const idempotencyKey = uuidv4();

  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      const charge = await omise.charges.create({
        ...chargeData,
        headers: {
          'Idempotency-Key': idempotencyKey
        }
      });

      console.log(`Charge created: ${charge.id}`);
      return charge;

    } catch (error) {
      const isServerError = error.statusCode >= 500;
      const isTimeout = error.code === 'ETIMEDOUT';
      const isLastAttempt = attempt === maxRetries - 1;

      if ((isServerError || isTimeout) && !isLastAttempt) {
        // Safe to retry with same key
        const delay = Math.pow(2, attempt) * 1000;
        await new Promise(resolve => setTimeout(resolve, delay));
        continue;
      }

      throw error;
    }
  }
}

// Usage
createChargeWithRetry({
  amount: 100000,
  currency: 'thb',
  card: 'tokn_test_...'
});

Go

package main

import (
    "fmt"
    "github.com/google/uuid"
    "github.com/omise/omise-go"
    "github.com/omise/omise-go/operations"
    "time"
)

func createChargeWithRetry(client *omise.Client, amount int64, currency, token string) (*omise.Charge, error) {
    // Generate unique idempotency key
    idempotencyKey := uuid.New().String()

    maxRetries := 3

    for attempt := 0; attempt < maxRetries; attempt++ {
        charge, err := client.CreateCharge(&operations.CreateCharge{
            Amount:   amount,
            Currency: currency,
            Card:     token,
            Headers: map[string]string{
                "Idempotency-Key": idempotencyKey,
            },
        })

        if err == nil {
            return charge, nil
        }

        // Check if retryable
        if omiseErr, ok := err.(*omise.Error); ok {
            if omiseErr.StatusCode >= 500 && attempt < maxRetries-1 {
                // Retry with exponential backoff
                delay := time.Duration(1<<uint(attempt)) * time.Second
                time.Sleep(delay)
                continue
            }
        }

        return nil, err
    }

    return nil, fmt.Errorf("max retries exceeded")
}

func main() {
    client, _ := omise.NewClient(
        os.Getenv("OMISE_PUBLIC_KEY"),
        os.Getenv("OMISE_SECRET_KEY"),
    )

    charge, err := createChargeWithRetry(client, 100000, "thb", "tokn_test_...")
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("Charge created: %s\n", charge.ID)
}

Idempotency Key Strategies

Strategy 1: UUID per Request (Recommended)

Generate a new UUID for each unique operation:

# Each charge gets unique key
charge1_key = SecureRandom.uuid
charge1 = create_charge(amount: 100_000, key: charge1_key)

charge2_key = SecureRandom.uuid
charge2 = create_charge(amount: 50_000, key: charge2_key)

Pros:

✅ Simple and safe
✅ No collision risk
✅ Works for all scenarios

Cons:

⚠️ Need to store key if you want to check status later

Strategy 2: Derived from Order ID

Base key on your internal order/transaction ID:

def get_idempotency_key(order_id):
    return f"order-{order_id}"

# Create charge for order
order_id = "ORD-12345"
idempotency_key = get_idempotency_key(order_id)

charge = omise.Charge.create(
    amount=100000,
    currency='thb',
    card=token,
    metadata={'order_id': order_id},
    headers={'Idempotency-Key': idempotency_key}
)

Pros:

✅ Easy to reconstruct key later
✅ Links charge to your system
✅ Can check if order was already charged

Cons:

⚠️ Need unique order IDs
⚠️ Can't retry with different parameters

Strategy 3: Store Key with Request

Save the key in your database:

// Store in database
const payment = await db.payments.create({
  order_id: 'ORD-12345',
  amount: 100000,
  idempotency_key: uuidv4(),
  status: 'pending'
});

// Use stored key for charge
const charge = await omise.charges.create({
  amount: payment.amount,
  currency: 'thb',
  card: token,
  headers: {
    'Idempotency-Key': payment.idempotency_key
  }
});

// Update status
await db.payments.update(payment.id, {
  status: 'completed',
  charge_id: charge.id
});

Pros:

✅ Can retry anytime (key stored)
✅ Audit trail
✅ Can correlate requests

Cons:

⚠️ More complex
⚠️ Requires database

Strategy 4: Hash of Request Parameters

Generate key from request content:

<?php
function getIdempotencyKey($chargeParams) {
    $content = json_encode($chargeParams);
    return hash('sha256', $content);
}

$chargeParams = [
    'amount' => 100000,
    'currency' => 'thb',
    'card' => $token,
    'metadata' => ['order_id' => 'ORD-12345']
];

$idempotencyKey = getIdempotencyKey($chargeParams);

$charge = OmiseCharge::create($chargeParams, [
    'Idempotency-Key' => $idempotencyKey
]);

Pros:

✅ Same parameters = same key automatically
✅ No storage needed
✅ Deterministic

Cons:

⚠️ Different parameters = different key (might want same charge)
⚠️ Sensitive to parameter order
⚠️ Token changes would change key

Key Expiration

24-Hour Lifetime

Idempotency keys are stored for 24 hours from first use:

# Day 1, 10:00 AM - First request
curl -H "Idempotency-Key: abc123" ...
# Creates new charge, key stored until Day 2, 10:00 AM

# Day 1, 11:00 AM - Retry
curl -H "Idempotency-Key: abc123" ...
# Returns cached result from 10:00 AM

# Day 2, 11:00 AM - After expiration
curl -H "Idempotency-Key: abc123" ...
# Key expired, creates NEW charge (different from first)

Key Expiration

After 24 hours, the same key will create a new resource. Don't reuse keys across different operations or after 24 hours.

Handling Expired Keys

# ❌ Bad - Reusing old key
def create_charge_for_order(order_id)
  # This key might be expired if order is old
  key = "order-#{order_id}"

  Omise::Charge.create({
    amount: 100000,
    currency: 'thb',
    card: token
  }, {
    'Idempotency-Key' => key
  })
end

# ✅ Good - Always use fresh key
def create_charge_for_order(order_id)
  # Combine order ID with timestamp
  key = "order-#{order_id}-#{Time.now.to_i}"

  Omise::Charge.create({
    amount: 100000,
    currency: 'thb',
    card: token,
    metadata: { order_id: order_id }
  }, {
    'Idempotency-Key' => key
  })
end

Retry Logic Best Practices

1. Retry Only Transient Errors

function isRetryable(error) {
  // Retry server errors
  if (error.statusCode >= 500) return true;

  // Retry timeouts
  if (error.code === 'ETIMEDOUT') return true;
  if (error.code === 'ECONNRESET') return true;

  // Don't retry client errors
  if (error.statusCode >= 400 && error.statusCode < 500) return false;

  return false;
}

async function chargeWithRetry(chargeData) {
  const idempotencyKey = uuidv4();
  const maxRetries = 3;

  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      return await omise.charges.create({
        ...chargeData,
        headers: { 'Idempotency-Key': idempotencyKey }
      });

    } catch (error) {
      if (!isRetryable(error) || attempt === maxRetries - 1) {
        throw error;
      }

      // Exponential backoff
      const delay = Math.pow(2, attempt) * 1000;
      await new Promise(resolve => setTimeout(resolve, delay));
    }
  }
}

2. Use Exponential Backoff

import time
import random

def exponential_backoff(attempt, base_delay=1, max_delay=60):
    """Calculate delay with jitter"""
    delay = min(base_delay * (2 ** attempt), max_delay)
    jitter = random.uniform(0, delay * 0.1)  # Add 10% jitter
    return delay + jitter

def create_charge_with_retry(charge_data, max_attempts=5):
    idempotency_key = str(uuid.uuid4())

    for attempt in range(max_attempts):
        try:
            return omise.Charge.create(
                **charge_data,
                headers={'Idempotency-Key': idempotency_key}
            )

        except omise.errors.BaseError as e:
            is_last_attempt = attempt == max_attempts - 1

            if e.http_status < 500 or is_last_attempt:
                raise

            # Wait before retry
            delay = exponential_backoff(attempt)
            time.sleep(delay)

    raise Exception("Max retries exceeded")

3. Set Timeouts

require 'timeout'

def create_charge_with_timeout(charge_params, timeout_seconds: 30)
  idempotency_key = SecureRandom.uuid

  begin
    Timeout.timeout(timeout_seconds) do
      Omise::Charge.create(
        charge_params,
        { 'Idempotency-Key' => idempotency_key }
      )
    end

  rescue Timeout::Error
    # Timeout - safe to retry with same key
    retry_charge(charge_params, idempotency_key)
  end
end

def retry_charge(params, key, max_retries: 3)
  max_retries.times do |attempt|
    begin
      return Omise::Charge.create(
        params,
        { 'Idempotency-Key' => key }
      )
    rescue Omise::Error => e
      raise unless e.http_status >= 500
      sleep(2 ** attempt)
    end
  end

  raise "Max retries exceeded"
end

4. Log Retry Attempts

const logger = require('./logger');

async function createChargeWithLogging(chargeData) {
  const idempotencyKey = uuidv4();
  const maxRetries = 3;

  logger.info('Creating charge', {
    idempotency_key: idempotencyKey,
    amount: chargeData.amount,
    currency: chargeData.currency
  });

  for (let attempt = 0; attempt < maxRetries; attempt++) {
    try {
      const charge = await omise.charges.create({
        ...chargeData,
        headers: { 'Idempotency-Key': idempotencyKey }
      });

      logger.info('Charge created successfully', {
        idempotency_key: idempotencyKey,
        charge_id: charge.id,
        attempt: attempt + 1
      });

      return charge;

    } catch (error) {
      logger.error('Charge attempt failed', {
        idempotency_key: idempotencyKey,
        attempt: attempt + 1,
        error_code: error.code,
        error_message: error.message,
        status_code: error.statusCode
      });

      const isRetryable = error.statusCode >= 500;
      const isLastAttempt = attempt === maxRetries - 1;

      if (!isRetryable || isLastAttempt) {
        logger.error('Charge failed permanently', {
          idempotency_key: idempotencyKey,
          total_attempts: attempt + 1
        });
        throw error;
      }

      const delay = Math.pow(2, attempt) * 1000;
      logger.info('Retrying charge', {
        idempotency_key: idempotencyKey,
        delay_ms: delay,
        next_attempt: attempt + 2
      });

      await new Promise(resolve => setTimeout(resolve, delay));
    }
  }
}

Advanced Patterns

Pattern 1: Distributed Systems

When multiple servers might retry the same operation:

# Use Redis to coordinate retries across servers
require 'redis'

class IdempotentChargeCreator
  def initialize(redis_client)
    @redis = redis_client
  end

  def create_charge(order_id, charge_params)
    # Try to acquire lock for this order
    lock_key = "charge_lock:#{order_id}"
    idempotency_key = "charge:#{order_id}"

    # Try to set lock (expires in 60 seconds)
    locked = @redis.set(lock_key, "locked", nx: true, ex: 60)

    unless locked
      # Another server is processing this
      return wait_for_charge(order_id)
    end

    begin
      # We got the lock - create charge
      charge = Omise::Charge.create(
        charge_params,
        { 'Idempotency-Key' => idempotency_key }
      )

      # Store result
      @redis.set("charge_result:#{order_id}", charge.to_json, ex: 86400)

      charge

    ensure
      # Release lock
      @redis.del(lock_key)
    end
  end

  private

  def wait_for_charge(order_id)
    # Wait for other server to finish
    10.times do
      result = @redis.get("charge_result:#{order_id}")
      return JSON.parse(result) if result

      sleep(0.5)
    end

    raise "Timeout waiting for charge"
  end
end

Pattern 2: Webhook Idempotency

Handle duplicate webhook deliveries:

# Webhooks can be delivered multiple times
# Use event ID as idempotency key

processed_events = set()  # Or use database/Redis

def handle_webhook(event_data):
    event_id = event_data['id']

    # Check if already processed
    if event_id in processed_events:
        print(f"Event {event_id} already processed")
        return

    # Process event
    if event_data['key'] == 'charge.complete':
        process_successful_charge(event_data['data'])

    # Mark as processed
    processed_events.add(event_id)

# Better: Store in database
def handle_webhook_persistent(event_data):
    event_id = event_data['id']

    # Try to insert (unique constraint on event_id)
    try:
        db.events.create({
            'event_id': event_id,
            'processed_at': datetime.now()
        })
    except UniqueConstraintError:
        # Already processed
        return

    # Process event
    process_event(event_data)

Pattern 3: Background Job Retries

Idempotent job processing:

// Using job queue (e.g., Bull, Sidekiq)
const queue = require('./queue');

queue.process('create-charge', async (job) => {
  const { order_id, amount, currency, token } = job.data;

  // Use job ID as part of idempotency key
  const idempotencyKey = `job-${job.id}-order-${order_id}`;

  try {
    const charge = await omise.charges.create({
      amount,
      currency,
      card: token,
      metadata: { order_id },
      headers: { 'Idempotency-Key': idempotencyKey }
    });

    // Store result
    await db.orders.update(order_id, {
      charge_id: charge.id,
      status: 'charged'
    });

    return { success: true, charge_id: charge.id };

  } catch (error) {
    if (error.statusCode >= 500) {
      // Retryable - job queue will retry
      throw error;
    } else {
      // Not retryable - mark order as failed
      await db.orders.update(order_id, {
        status: 'failed',
        error: error.message
      });

      return { success: false, error: error.message };
    }
  }
});

// Add job
queue.add('create-charge', {
  order_id: 'ORD-12345',
  amount: 100000,
  currency: 'thb',
  token: 'tokn_test_...'
}, {
  attempts: 5,
  backoff: {
    type: 'exponential',
    delay: 2000
  }
});

Testing Idempotency

Test Duplicate Requests

# Test that duplicate requests return same result
describe 'Idempotency' do
  it 'returns same charge for duplicate requests' do
    idempotency_key = SecureRandom.uuid

    # First request
    charge1 = Omise::Charge.create({
      amount: 100000,
      currency: 'thb',
      card: token
    }, {
      'Idempotency-Key' => idempotency_key
    })

    # Duplicate request
    charge2 = Omise::Charge.create({
      amount: 100000,
      currency: 'thb',
      card: token
    }, {
      'Idempotency-Key' => idempotency_key
    })

    # Should be the same charge
    expect(charge2.id).to eq(charge1.id)
    expect(charge2.amount).to eq(charge1.amount)
  end

  it 'creates new charge with different key' do
    # First request
    charge1 = Omise::Charge.create({
      amount: 100000,
      currency: 'thb',
      card: token
    }, {
      'Idempotency-Key' => SecureRandom.uuid
    })

    # Different key
    charge2 = Omise::Charge.create({
      amount: 100000,
      currency: 'thb',
      card: token
    }, {
      'Idempotency-Key' => SecureRandom.uuid
    })

    # Should be different charges
    expect(charge2.id).not_to eq(charge1.id)
  end
end

Simulate Network Errors

// Test retry logic
const nock = require('nock');

describe('Idempotent Retry', () => {
  it('retries on server error', async () => {
    const idempotencyKey = uuidv4();

    // First request fails
    nock('https://api.omise.co')
      .post('/charges')
      .matchHeader('Idempotency-Key', idempotencyKey)
      .reply(500, { error: 'Internal Server Error' });

    // Retry succeeds
    nock('https://api.omise.co')
      .post('/charges')
      .matchHeader('Idempotency-Key', idempotencyKey)
      .reply(200, {
        object: 'charge',
        id: 'chrg_test_123',
        amount: 100000
      });

    const charge = await createChargeWithRetry({
      amount: 100000,
      currency: 'thb',
      card: 'tokn_test_...'
    });

    expect(charge.id).toBe('chrg_test_123');
  });
});

Common Mistakes

❌ Don't: Reuse Keys Across Operations

# ❌ Bad - Same key for different operations
idempotency_key = "my-key"

charge1 = omise.Charge.create(
    amount=100000,
    headers={'Idempotency-Key': idempotency_key}
)

charge2 = omise.Charge.create(
    amount=50000,  # Different amount!
    headers={'Idempotency-Key': idempotency_key}
)
# charge2 will return charge1's result!

# ✅ Good - Unique key per operation
charge1 = omise.Charge.create(
    amount=100000,
    headers={'Idempotency-Key': str(uuid.uuid4())}
)

charge2 = omise.Charge.create(
    amount=50000,
    headers={'Idempotency-Key': str(uuid.uuid4())}
)

❌ Don't: Forget to Handle Cached Errors

# ❌ Bad - Original request failed, retry returns same error
idempotency_key = SecureRandom.uuid

begin
  Omise::Charge.create({
    amount: 100,  # Too small!
    currency: 'thb'
  }, {
    'Idempotency-Key' => idempotency_key
  })
rescue Omise::Error => e
  # Retry with fixed amount but same key
  Omise::Charge.create({
    amount: 100000,  # Fixed amount
    currency: 'thb'
  }, {
    'Idempotency-Key' => idempotency_key  # Same key = cached error!
  })
  # Returns same error, not new charge
end

# ✅ Good - Use new key for corrected request
begin
  Omise::Charge.create({
    amount: 100,
    currency: 'thb'
  }, {
    'Idempotency-Key' => SecureRandom.uuid
  })
rescue Omise::Error => e
  # Use NEW key for fixed request
  Omise::Charge.create({
    amount: 100000,
    currency: 'thb'
  }, {
    'Idempotency-Key' => SecureRandom.uuid  # New key!
  })
end

❌ Don't: Retry Client Errors

// ❌ Bad - Retrying invalid request
async function badRetry() {
  const idempotencyKey = uuidv4();

  for (let i = 0; i < 3; i++) {
    try {
      return await omise.charges.create({
        amount: 100,  // Too small - will always fail!
        currency: 'thb',
        headers: { 'Idempotency-Key': idempotencyKey }
      });
    } catch (error) {
      // Retrying won't help - request is invalid
      continue;
    }
  }
}

// ✅ Good - Only retry server errors
async function goodRetry(chargeData) {
  const idempotencyKey = uuidv4();

  for (let i = 0; i < 3; i++) {
    try {
      return await omise.charges.create({
        ...chargeData,
        headers: { 'Idempotency-Key': idempotencyKey }
      });
    } catch (error) {
      // Only retry server errors
      if (error.statusCode < 500) {
        throw error;  // Don't retry client errors
      }
      // Continue retry loop for server errors
    }
  }
}

Quick Reference

Idempotency Header

Idempotency-Key: <unique-string>

When to Use

Request Type	Use Idempotency?
POST (create)	✅ Always
PATCH (update)	✅ Recommended
GET (read)	❌ Not needed
DELETE	❌ Not needed

Key Lifetime

Stored: 24 hours from first use
Expired: Creates new resource after 24 hours

Retry Decision Tree

Request failed?
├─ Yes → Check error type
│   ├─ 5xx Server Error → Retry with SAME key
│   ├─ Network timeout → Retry with SAME key
│   ├─ 4xx Client Error → Fix request, use NEW key
│   └─ Other error → Don't retry
└─ No → Success!

Example Implementation

def create_charge_idempotently(params)
  key = SecureRandom.uuid

  Omise::Charge.create(
    params,
    { 'Idempotency-Key' => key }
  )
rescue Omise::Error => e
  raise unless e.http_status >= 500

  # Retry with same key
  Omise::Charge.create(
    params,
    { 'Idempotency-Key' => key }
  )
end

Next: Learn about API Versioning to manage version changes and maintain backward compatibility.

Overview​

What is Idempotency?​

Without Idempotency​

With Idempotency​

How Idempotency Works​

Example Flow​

When to Use Idempotency​

Always Use For:​

Not Needed For:​

Idempotency-Key Header​

Header Format​

Key Requirements​

Recommended: Use UUIDs​

Implementation Examples​

Ruby​

Python​

PHP​

Node.js​

Go​

Idempotency Key Strategies​

Strategy 1: UUID per Request (Recommended)​

Strategy 2: Derived from Order ID​

Strategy 3: Store Key with Request​

Strategy 4: Hash of Request Parameters​

Key Expiration​

24-Hour Lifetime​

Handling Expired Keys​

Retry Logic Best Practices​

1. Retry Only Transient Errors​

2. Use Exponential Backoff​

3. Set Timeouts​

4. Log Retry Attempts​

Advanced Patterns​

Pattern 1: Distributed Systems​

Pattern 2: Webhook Idempotency​

Pattern 3: Background Job Retries​

Testing Idempotency​

Test Duplicate Requests​

Simulate Network Errors​

Common Mistakes​

❌ Don't: Reuse Keys Across Operations​

❌ Don't: Forget to Handle Cached Errors​

❌ Don't: Retry Client Errors​

Quick Reference​

Idempotency Header​

When to Use​

Key Lifetime​

Retry Decision Tree​

Example Implementation​

Related Resources​

Overview

What is Idempotency?

Without Idempotency

With Idempotency

How Idempotency Works

Example Flow

When to Use Idempotency

Always Use For:

Not Needed For:

Idempotency-Key Header

Header Format

Key Requirements

Recommended: Use UUIDs

Implementation Examples

Ruby

Python

PHP

Node.js

Go

Idempotency Key Strategies

Strategy 1: UUID per Request (Recommended)

Strategy 2: Derived from Order ID

Strategy 3: Store Key with Request

Strategy 4: Hash of Request Parameters

Key Expiration

24-Hour Lifetime

Handling Expired Keys

Retry Logic Best Practices

1. Retry Only Transient Errors

2. Use Exponential Backoff

3. Set Timeouts

4. Log Retry Attempts

Advanced Patterns

Pattern 1: Distributed Systems

Pattern 2: Webhook Idempotency

Pattern 3: Background Job Retries

Testing Idempotency

Test Duplicate Requests

Simulate Network Errors

Common Mistakes

❌ Don't: Reuse Keys Across Operations

❌ Don't: Forget to Handle Cached Errors

❌ Don't: Retry Client Errors

Quick Reference

Idempotency Header

When to Use

Key Lifetime

Retry Decision Tree

Example Implementation

Related Resources