Resiliency policies

Define timeouts, retries, and circuit breaker policies under policies. Each policy is given a name so you can refer to them from the targets section in the resiliency spec.

Note: Dapr offers default retries for specific APIs. See here to learn how you can overwrite default retry logic with user defined retry policies.

Timeouts

Timeouts are optional policies that can be used to early-terminate long-running operations. If you’ve exceeded a timeout duration:

• The operation in progress is terminated (if possible).
• An error is returned.

Valid values are of the form accepted by Go’s time.ParseDuration, for example: 15s, 2m, 1h30m. Timeouts have no set maximum value.

Example:

spec:
  policies:
    # Timeouts are simple named durations.
    timeouts:
      general: 5s
      important: 60s
      largeResponse: 10s

If you don’t specify a timeout value, the policy does not enforce a time and defaults to whatever you set up per the request client.

Retries

With retries, you can define a retry strategy for failed operations, including requests failed due to triggering a defined timeout or circuit breaker policy. The following retry options are configurable:

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
}

Example:

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

Circuit Breakers

Circuit Breaker (CB) policies are used when other applications/services/components are experiencing elevated failure rates. CBs monitor the requests and shut off all traffic to the impacted service when a certain criteria is met (“open” state). By doing this, CBs give the service time to recover from their outage instead of flooding it with events. The CB can also allow partial traffic through to see if the system has healed (“half-open” state). Once requests resume being successful, the CB gets into “closed” state and allows traffic to completely resume.

Example:

spec:
  policies:
    circuitBreakers:
      pubsubCB:
        maxRequests: 1
        interval: 8s
        timeout: 45s
        trip: consecutiveFailures > 8

Overriding default retries

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

Setting default policies

In resiliency you can set default policies, which have a broad scope. This is done through reserved keywords that let Dapr know when to apply the policy. There are 3 default policy types:

• DefaultRetryPolicy
• DefaultTimeoutPolicy
• DefaultCircuitBreakerPolicy

If these policies are defined, they are used for every operation to a service, application, or component. They can also be modified to be more specific through the appending of additional keywords. The specific policies follow the following pattern, Default%sRetryPolicy, Default%sTimeoutPolicy, and Default%sCircuitBreakerPolicy. Where the %s is replaced by a target of the policy.

Below is a table of all possible default policy keywords and how they translate into a policy name.

Policy hierarchy resolution

Default policies are applied if the operation being executed matches the policy type and if there is no more specific policy targeting it. For each target type (app, actor, and component), the policy with the highest priority is a Named Policy, one that targets that construct specifically.

If none exists, the policies are applied from most specific to most broad.

How default policies and built-in retries work together

In the case of the built-in retries, default policies do not stop the built-in retry policies from running. Both are used together but only under specific circumstances.

For service and actor invocation, the built-in retries deal specifically with issues connecting to the remote sidecar (when needed). As these are important to the stability of the Dapr runtime, they are not disabled unless a named policy is specifically referenced for an operation. In some instances, there may be additional retries from both the built-in retry and the default retry policy, but this prevents an overly weak default policy from reducing the sidecar’s availability/success rate.

Policy resolution hierarchy for applications, from most specific to most broad:

1. Named Policies in App Targets
2. Default App Policies / Built-In Service Retries
3. Default Policies / Built-In Service Retries

Policy resolution hierarchy for actors, from most specific to most broad:

1. Named Policies in Actor Targets
2. Default Actor Policies / Built-In Actor Retries
3. Default Policies / Built-In Actor Retries

Policy resolution hierarchy for components, from most specific to most broad:

1. Named Policies in Component Targets
2. Default Component Type + Component Direction Policies / Built-In Actor Reminder Retries (if applicable)
3. Default Component Direction Policies / Built-In Actor Reminder Retries (if applicable)
4. Default Component Policies / Built-In Actor Reminder Retries (if applicable)
5. Default Policies / Built-In Actor Reminder Retries (if applicable)

As an example, take the following solution consisting of three applications, three components and two actor types:

Applications:

• AppA
• AppB
• AppC

Components:

• Redis Pubsub: pubsub
• Redis statestore: statestore
• CosmosDB Statestore: actorstore

Actors:

• EventActor
• SummaryActor

Below is policy that uses both default and named policies as applies these to the targets.

spec:
  policies:
    retries:
      # Global Retry Policy
      DefaultRetryPolicy:
        policy: constant
        duration: 1s
        maxRetries: 3
      
      # Global Retry Policy for Apps
      DefaultAppRetryPolicy:
        policy: constant
        duration: 100ms
        maxRetries: 5

      # Global Retry Policy for Apps
      DefaultActorRetryPolicy:
        policy: exponential
        maxInterval: 15s
        maxRetries: 10

      # Global Retry Policy for Inbound Component operations
      DefaultComponentInboundRetryPolicy:
        policy: constant
        duration: 5s
        maxRetries: 5

      # Global Retry Policy for Statestores
      DefaultStatestoreComponentOutboundRetryPolicy:
        policy: exponential
        maxInterval: 60s
        maxRetries: -1

     # Named policy
      fastRetries:
        policy: constant
        duration: 10ms
        maxRetries: 3

     # Named policy
      retryForever:
        policy: exponential
        maxInterval: 10s
        maxRetries: -1

  targets:
    apps:
      appA:
        retry: fastRetries

      appB:
        retry: retryForever
    
    actors:
      EventActor:
        retry: retryForever

    components:
      actorstore:
        retry: fastRetries

The table below is a break down of which policies are applied when attempting to call the various targets in this solution.

下一步

Try out one of the Resiliency quickstarts:

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