HttpUtils with Polly

Hi,
How can we use HttpUtils with Polly to implement retries/backoff? We’re having issues calling an API on Azure giving 429 Too many requests.

We’re thinking of the methods such as GetJsonFromUrl. It is HttpClient under the hood, so it should be doable, right?

HTTP Utils uses HttpClient from .NET 6+. I’ve not used Polly to know how to best integrate it with HTTP Utils, but if needed you can change the HttpClientHandler or HttpClient used by overriding these factory functions:

HttpUtils.HttpClientHandlerFactory = () => new HttpClientHandler {
    UseDefaultCredentials = true,
    AutomaticDecompression = DecompressionMethods.Brotli 
        | DecompressionMethods.Deflate | DecompressionMethods.GZip,
};

HttpUtils.CreateClient = () => {
    var httpClient = new HttpClient();
    return httpClient;
};
1 Like

This is how I ended up doing it, after I found out that Polly actually catches exceptions, and therefore is compatible with HttpUtils:

Define the retry policy, in this example we only catch 429, then wait for a relatively long time (a bit randomized) before retrying.

var delay = Backoff
           .DecorrelatedJitterBackoffV2(
               medianFirstRetryDelay: TimeSpan.FromSeconds(10),
               retryCount
           );
policyS = Policy
               .Handle<HttpRequestException>(ex => ex.Message.Contains("429"))
               .WaitAndRetry(
                   delay,
                   (result, timespan, retryNo, context) => {
                       Console.WriteLine($"{context.OperationKey}: Retry number {retryNo} within " +
                           $"{timespan.TotalMilliseconds}ms. Original status code: 429");
                   }
               );

The actual API call is here:

var response = policyS.Execute(ctx => {
                    var response2 = lookupUrl.GetJsonFromUrl(
                      requestFilter: x => {
                          x.AddHeader("x-authorization", $"Bearer {ccToken}");
                      });
                    return response2.FromJson<LookupDTO>();
                }, pollyContext);
1 Like

Cool, thx for Sharing!