Implement a retry policy with Go

Any application that runs in the cloud or communicates with remote services and resources must be able to handle transient faults. It's common for these applications to experience faults due to a momentary loss of network connectivity, a request timeout when a service or resource is busy, or other factors. Developers should build applications to handle transient faults transparently to improve stability and resiliency.

In this article, you learn how to use the Azure Storage client module for Go to configure a retry policy for an application that connects to Azure Blob Storage. Retry policies define how the application handles failed requests, and should always be tuned to match the business requirements of the application and the nature of the failure.

Configure retry options

Retry policies for Blob Storage are configured programmatically, offering control over how retry options are applied to various service requests and scenarios. For example, a web app issuing requests based on user interaction might implement a policy with fewer retries and shorter delays to increase responsiveness and notify the user when an error occurs. Alternatively, an app or component running batch requests in the background might increase the number of retries and use an exponential backoff strategy to allow the request time to complete successfully.

The following table lists the fields available to configure in a RetryOptions instance, along with the type, a brief description, and the default value if you make no changes. You should be proactive in tuning the values of these properties to meet the needs of your app.

Property	Type	Description	Default value
MaxRetries	int32	Optional. Specifies the maximum number of attempts a failed operation is retried before producing an error. A value less than zero means one try and no retries.	3
TryTimeout	time.Duration	Optional. Indicates the maximum time allowed for any single try of an HTTP request. Specify a value greater than zero to enable. Note: Setting this field to a small value might cause premature HTTP request timeouts.	Disabled by default.
RetryDelay	time.Duration	Optional. Specifies the initial amount of delay to use before retrying an operation. The value is used only if the HTTP response doesn't contain a Retry-After header. The delay increases exponentially with each retry up to the maximum specified by MaxRetryDelay. A value less than zero means no delay between retries.	4 seconds
MaxRetryDelay	time.Duration	Optional. Specifies the maximum delay allowed before retrying an operation. Typically, the value is greater than or equal to the value specified in RetryDelay. A value less than zero means there's no maximum.	60 seconds
StatusCodes	[]int	Optional. Specifies the HTTP status codes that indicate the operation should be retried. Specifying values replaces the default values. Specifying an empty slice disables retries for HTTP status codes.	408 - http.StatusRequestTimeout 429 - http.StatusTooManyRequests 500 - http.StatusInternalServerError 502 - http.StatusBadGateway 503 - http.StatusServiceUnavailable 504 - http.StatusGatewayTimeout
ShouldRetry	func(*http.Response, error) bool	Optional. evaluates if the retry policy should retry the request. When specified, the function overrides comparison against the list of HTTP status codes and error checking within the retry policy. Context and NonRetriable errors remain evaluated before calling ShouldRetry. The *http.Response and error parameters are mutually exclusive, that is, if one is nil, the other isn't nil. A return value of true means the retry policy should retry.

To work with the code example in this article, add the following import paths to your code:

import (
	"context"
	"time"

	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
	"github.com/Azure/azure-sdk-for-go/sdk/azcore/policy"
	"github.com/Azure/azure-sdk-for-go/sdk/azidentity"
	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob"
)

In the following code example, we configure the retry options in an instance of RetryOptions, include it in a ClientOptions instance, and create a new client object:

options := azblob.ClientOptions{
	ClientOptions: azcore.ClientOptions{
		Retry: policy.RetryOptions{
			MaxRetries:    10,
			TryTimeout:    time.Minute * 15,
			RetryDelay:    time.Second * 1,
			MaxRetryDelay: time.Second * 60,
			StatusCodes:   []int{408, 429, 500, 502, 503, 504},
		},
	},
}

credential, err := azidentity.NewDefaultAzureCredential(nil)
handleError(err)

client, err := azblob.NewClient(accountURL, credential, &options)
handleError(err)

In this example, each service request issued from client uses the retry options as defined in the RetryOptions struct. This policy applies to client requests. You can configure various retry strategies for service clients based on the needs of your app.

Related content

• For architectural guidance and general best practices for retry policies, see Transient fault handling.
• For guidance on implementing a retry pattern for transient failures, see Retry pattern.