AddPolicyHandler() method is what adds policies to the
HttpClient
objects you’ll use. In this
case, it’s adding a Polly’s policy for Http Retries with exponential backoff.
To have a more modular approach, the Http Retry Policy can be defined in a separate method within
the
Program.cs file, as shown in the following code:
static IAsyncPolicy GetRetryPolicy
()
{
return HttpPolicyExtensions
.
HandleTransientHttpError
()
.
OrResult
(msg => msg.
StatusCode
== System.
Net
.
HttpStatusCode
.
NotFound
)
.
WaitAndRetryAsync
(
6
, retryAttempt => TimeSpan.
FromSeconds
(Math.
Pow
(
2
,
retryAttempt)));
}
With Polly, you can define a Retry policy with the number of retries, the exponential backoff
configuration, and the actions to take when there’s an HTTP exception, such as logging the error. In
this case, the policy is configured to try six times with an exponential retry, starting at two seconds.
Add a jitter strategy to the retry policy A regular Retry policy can affect your system in cases of high concurrency and scalability and under
high contention. To overcome peaks of similar retries coming from many clients in partial outages, a
good workaround is to add a jitter strategy to the retry algorithm/policy. This strategy can improve
the overall performance of the end-to-end system. As recommended in
Polly: Retry with Jitter
, a good
jitter strategy can be implemented by smooth and evenly distributed retry intervals applied with a
well-controlled median initial retry delay on an exponential backoff. This approach helps to spread out
the spikes when the issue arises. The principle is illustrated by the following example:
var
delay = Backoff.
DecorrelatedJitterBackoffV2
(medianFirstRetryDelay:
TimeSpan.
FromSeconds
(
1
), retryCount:
5
);
var
retryPolicy = Policy
.
Handle
()
.
WaitAndRetryAsync
(delay);
