ASP.NET Core 異常重試組件 Polly

Polly 是一種 .NET 彈性和瞬態故障處理庫，允許開發人員以流暢和線程安全的方式表達策略，如重試，斷路器，超時，隔離隔離和備用，Polly 適用於 .NET 4.0，.NET 4.5 和 .NET Standard 1.1。

安裝 Nuget 程序包：

Install-Package Polly

簡單使用：

// Execute an action
var policy = Policy
              .Handle<Exception>()
              .RetryAsync(10, async (exception, retryCount) =>
              {
                  await LogAsync(exception, $"第{retryCount}次重試");
              });

await policy.ExecuteAsync(async () => await DoSomething());

//另外一種使用方式：
var tokenResponse = await Policy
        .Handle<Exception>()
        .OrResult<TokenResponse>(x => x.IsError)
        .RetryAsync(5) //如果使用Retry，會報錯誤：Please use asynchronous-defined policies when calling asynchronous ExecuteAsync (and similar) methods
        .ExecuteAsync(async () =>
        {
            var client = new DiscoveryClient(_appSettings.IssuerUri);
            client.Policy.RequireHttps = false;
            var disco = await client.GetAsync();
            var tokenClient = new TokenClient(disco.TokenEndpoint, clientId, clientSecret);
            return await tokenClient.RequestRefreshTokenAsync(refreshToken);
        });

參考資料：

• Polly Github
• Implementing the retry pattern in c sharp using Polly