Retry and back-off resiliency policies

• 1: Retry resiliency policies
• 2: Override default retry resiliency policies

1 - Retry resiliency policies

Requests can fail due to transient errors, like encountering network congestion, reroutes to overloaded instances, and more. Sometimes, requests can fail due to other resiliency policies set in place, like triggering a defined timeout or circuit breaker policy.

In these cases, configuring retries can either:

• Send the same request to a different instance, or
• Retry sending the request after the condition has cleared.

Retries and timeouts work together, with timeouts ensuring your system fails fast when needed, and retries recovering from temporary glitches.

Dapr provides default resiliency policies, which you can overwrite with user-defined retry policies.

Retry policy format

Example 1

spec:
  policies:
    # Retries are named templates for retry configurations and are instantiated for life of the operation.
    retries:
      pubsubRetry:
        policy: constant
        duration: 5s
        maxRetries: 10

      retryForever:
        policy: exponential
        maxInterval: 15s
        maxRetries: -1 # Retry indefinitely

Example 2

spec:
  policies:
    retries:
      retry5xxOnly:
        policy: constant
        duration: 5s
        maxRetries: 3
        matching:
          httpStatusCodes: "429,500-599" # retry the HTTP status codes in this range. All others are not retried. 
          gRPCStatusCodes: "1-4,8-11,13,14" # retry gRPC status codes in these ranges and separate single codes.

Spec metadata

The following retry options are configurable:

Exponential back-off policy

The exponential back-off window uses the following formula:

BackOffDuration = PreviousBackOffDuration * (Random value from 0.5 to 1.5) * 1.5
if BackOffDuration > maxInterval {
  BackoffDuration = maxInterval
}

Retry status codes

When applications span multiple services, especially on dynamic environments like Kubernetes, services can disappear for all kinds of reasons and network calls can start hanging. Status codes provide a glimpse into our operations and where they may have failed in production.

HTTP

The following table includes some examples of HTTP status codes you may receive and whether you should or should not retry certain operations.

gRPC

The following table includes some examples of gRPC status codes you may receive and whether you should or should not retry certain operations.

Retry filter based on status codes

The retry filter enables granular control over retry policies by allowing users to specify HTTP and gRPC status codes or ranges for which retries should apply.

spec:
  policies:
    retries:
      retry5xxOnly:
        # ...
        matching:
          httpStatusCodes: "429,500-599" # retry the HTTP status codes in this range. All others are not retried. 
          gRPCStatusCodes: "4,8-11,13,14" # retry gRPC status codes in these ranges and separate single codes.

Demo

Watch a demo presented during Diagrid’s Dapr v1.15 celebration to see how to set retry status code filters using Diagrid Conductor

Next steps

• [Learn how to override default retry policies for specific APIs.]({[< ref override-default-retries.md >]})
• Learn how to target your retry policies from the resiliency spec.
• Learn more about:
  • Timeout policies
  • Circuit breaker policies

Related links

Try out one of the Resiliency quickstarts:

• Resiliency: Service-to-service
• Resiliency: State Management

2 - Override default retry resiliency policies

Dapr provides default retries for any unsuccessful request, such as failures and transient errors. Within a resiliency spec, you have the option to override Dapr’s default retry logic by defining policies with reserved, named keywords. For example, defining a policy with the name DaprBuiltInServiceRetries, overrides the default retries for failures between sidecars via service-to-service requests. Policy overrides are not applied to specific targets.

Note: Although you can override default values with more robust retries, you cannot override with lesser values than the provided default value, or completely remove default retries. This prevents unexpected downtime.

Below is a table that describes Dapr’s default retries and the policy keywords to override them:

The resiliency spec example below shows overriding the default retries for all service invocation requests by using the reserved, named keyword ‘DaprBuiltInServiceRetries’.

Also defined is a retry policy called ‘retryForever’ that is only applied to the appB target. appB uses the ‘retryForever’ retry policy, while all other application service invocation retry failures use the overridden ‘DaprBuiltInServiceRetries’ default policy.

spec:
  policies:
    retries:
      DaprBuiltInServiceRetries: # Overrides default retry behavior for service-to-service calls
        policy: constant
        duration: 5s
        maxRetries: 10

      retryForever: # A user defined retry policy replaces default retries. Targets rely solely on the applied policy. 
        policy: exponential
        maxInterval: 15s
        maxRetries: -1 # Retry indefinitely

  targets:
    apps:
      appB: # app-id of the target service
        retry: retryForever

Related links

Try out one of the Resiliency quickstarts:

• Resiliency: Service-to-service
• Resiliency: State Management