Retry

Retry is a resiliency pattern that enables an application to shield transient issues from customers. This is done by retrying requests that are failing from temporary faults such as a pod is starting up. This guide describes how to implement retry policy in FSM.

Configuring Retry

FSM uses its Retry policy API to allow retries on traffic from a specified source (ServiceAccount) to one or more destinations (Service). Retry is only applicable to HTTP traffic. FSM can implement retry for applications participating in the mesh.

The following retry configurations are supported:

• Per Try Timeout: The time allowed for a retry to take before it is considered a failed attempt. The default uses the global route timeout.

• Retry Backoff Base Interval: The base interval for exponential retry back-off. The backoff is randomly chosen from the range [0,(2**N-1)B], where N is the retry number and B is the base interval. The default is 25ms and the maximum interval is 10 times the base interval.

• Number of Retries: The maximum number of retries to attempt. The default is 1.

• Retry On: Specifies the policy for when a failed request will be retried. Multiple policies can be specified by using a , delimited list.

To learn more about configuring retry, refer to the Retry policy demo and [API documentation][1].

Examples

If requests from the bookbuyer service to bookstore-v1 service or bookstore-v2 service receive responses with a status code 5xx, then bookbuyer will retry the request 3 times. If an attempted retry takes longer than 3s it’s considered a failed attempt. Each retry has a delay period (backoff) before it is attempted calculated above. The backoff for all retries is capped at 10s.

kind: Retry
apiVersion: policy.flomesh.io/v1alpha1
metadata:
  name: retry
spec:
  source:
    kind: ServiceAccount
    name: bookbuyer
    namespace: bookbuyer
  destinations:
  - kind: Service
    name: bookstore
    namespace: bookstore-v1
  - kind: Service
    name: bookstore
    namespace: bookstore-v2
  retryPolicy:
    retryOn: "5xx"
    perTryTimeout: 3s
    numRetries: 3
    retryBackoffBaseInterval: 1s

If requests from the bookbuyer service to bookstore-v2 service receive responses with a status code 5xx or retriable-4xx (409), then bookbuyer will retry the request 5 times. If an attempted retry takes longer than 4s it’s considered a failed attempt. Each retry has a delay period (backoff) before it is attempted calculated above. The backoff for all retries is capped at 20ms.

kind: Retry
apiVersion: policy.flomesh.io/v1alpha1
metadata:
  name: retry
spec:
  source:
    kind: ServiceAccount
    name: bookbuyer
    namespace: bookbuyer
  destinations:
  - kind: Service
    name: bookstore
    namespace: bookstore-v2
  retryPolicy:
    retryOn: "5xx,retriable-4xx"
    perTryTimeout: 4s
    numRetries: 5
    retryBackoffBaseInterval: 2ms