What is a retry policy?

What is a retry policy and why is it important?

A retry policy is a set of attributes that dictate how a system should handle a failed workflow or activity task. It is crucial because it helps ensure that a flow doesn't fail due to intermittent issues, thereby improving the overall reliability and user experience of the system.

Retry policies can apply to various types of failures, such as HTTP status codes 408, 429, and 5xx, as well as connectivity issues. By implementing a retry policy, systems can automatically attempt to resolve temporary failures without requiring manual intervention.

How do different platforms implement retry policies?

Different platforms have their own implementations of retry policies to handle transient failures. Here are some examples:

• Power Automate: The default policy retries four times, but this can be customized. Users can create custom policies to control the number of retries and the interval between them.
• Amazon QLDB: The driver automatically retries failed transactions to handle transient exceptions like CapacityExceededException and RateExceededException.
• LivePerson Developer Center: The Connector API resends failed ms.MessagingEventNotification.ContentEvent events up to three times. However, ms.MessagingEventNotification.RichContentEvent events are dropped immediately if the first attempt fails.
• Azure Logic Apps: The default retry policy is exponential, with up to four retries at increasing intervals.
• ServiceNow: Users can set a retry policy to automatically retry failed requests that encounter intermittent issues like network failures or request rate limits.

What are some best practices for implementing retry policies?

Implementing retry policies effectively requires adhering to several best practices to ensure they are both efficient and effective.

These best practices include matching the retry policy to the application's business requirements, using exponential backoff, differentiating between error codes, including randomization, and avoiding too many retries.

Why is exponential backoff recommended in retry policies?

Exponential backoff is recommended because it uses longer intervals between retries, which helps to reduce the load on the system and increases the chances of a successful retry. This approach waits a short time before the first retry and then exponentially increases the time between each subsequent retry.

This method helps to prevent overwhelming the system with too many retry attempts in a short period, thereby improving the overall stability and performance of the application.

How should retry policies differentiate between error codes?

Retry policies should differentiate between client-side errors (4xx codes) and server-side errors (5xx codes). This differentiation is important because retry logic should primarily target server-side errors, which often indicate temporary issues that can be resolved with a retry.

• Client-side errors: These errors usually indicate issues with the request itself, such as invalid input or authentication problems, and should not be retried.
• Server-side errors: These errors often indicate temporary issues on the server, such as overload or downtime, and are suitable candidates for retry attempts.
• Transient errors: Errors like network timeouts or rate limiting by cloud services are often temporary and can be resolved with retries.

What role does randomization play in retry policies?

Randomization plays a crucial role in retry policies by preventing multiple instances of the client from sending subsequent retry attempts at the same time. This helps to avoid creating a "thundering herd" problem, where simultaneous retries can overwhelm the system.

By introducing randomization, each retry attempt is slightly staggered, reducing the likelihood of simultaneous retries and improving the chances of a successful retry.

Why is it important to avoid too many retries?

Avoiding too many retries is important because too short intervals or too many retries can negatively impact the service or target resource. Excessive retries can lead to increased load on the system, potentially causing further failures and degrading overall performance.

It is essential to balance the number of retries and the intervals between them to ensure that the retry policy is effective without overloading the system.

How do retry policies improve service availability?

Retry policies improve service availability by attempting failed operations again, allowing applications to handle temporary failures such as network loss, rate limiting by cloud services, and timeouts. This resiliency technique helps to ensure that services remain available and responsive, even in the face of intermittent issues.

By automatically retrying failed operations, retry policies reduce the need for manual intervention and improve the overall user experience, making systems more robust and reliable.