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Adds fault tolerance. Polly v8 + MS.Extensions.Http.Resilience, retry/circuit breaker/timeout.
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| name | dotnet-resilience |
| description | Adds fault tolerance. Polly v8 + MS.Extensions.Http.Resilience, retry/circuit breaker/timeout. |
| license | MIT |
| targets | ["*"] |
| tags | ["architecture","dotnet","skill"] |
| version | 0.0.1 |
| author | dotnet-agent-harness |
| invocable | true |
| claudecode | {"allowed-tools":["Read","Grep","Glob","Bash","Write","Edit"]} |
| codexcli | {"short-description":".NET skill guidance for architecture tasks"} |
| opencode | {"allowed-tools":["Read","Grep","Glob","Bash","Write","Edit"]} |
| copilot | {} |
| geminicli | {} |
| antigravity | {} |
| category | fundamentals |
| subcategory | coding-standards |
Modern resilience patterns for .NET applications using Polly v8 and Microsoft.Extensions.Http.Resilience. Covers the
standard resilience pipeline (rate limiter, total timeout, retry, circuit breaker, attempt timeout), custom pipeline
configuration, and integration with the .NET dependency injection system.
Superseded package: Microsoft.Extensions.Http.Polly is superseded by Microsoft.Extensions.Http.Resilience. Do
not use Microsoft.Extensions.Http.Polly for new projects. See the
migration guide for
upgrading existing code.
Cross-references: [skill:dotnet-csharp-dependency-injection] for service registration, [skill:dotnet-csharp-async-patterns] for cancellation token propagation, [skill:dotnet-http-client] for applying resilience to HTTP clients.
| Package | Status | Purpose |
|---|---|---|
Polly (v8+) | Current | Core resilience library -- strategies, pipelines, telemetry |
Microsoft.Extensions.Resilience | Current | DI integration for non-HTTP resilience pipelines |
Microsoft.Extensions.Http.Resilience | Current | DI integration for IHttpClientFactory resilience pipelines |
Microsoft.Extensions.Http.Polly | Superseded | Legacy HTTP resilience -- migrate to Microsoft.Extensions.Http.Resilience |
Polly (v7 and earlier) | Legacy | Older API -- migrate to v8 |
Install the modern stack:
<PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="9.*" />
<!-- Transitively brings in Polly v8 and Microsoft.Extensions.Resilience -->
```xml
For non-HTTP scenarios only:
```xml
<PackageReference Include="Microsoft.Extensions.Resilience" Version="9.*" />
```xml
---
## Standard Resilience Pipeline
`Microsoft.Extensions.Http.Resilience` provides a standard resilience pipeline that follows the recommended order. The pipeline layers execute from outermost to innermost:
```text
Request
--> Rate Limiter (1. shed excess load)
--> Total Timeout (2. cap total wall-clock time)
--> Retry (3. retry transient failures)
--> Circuit Breaker (4. stop calling failing services)
--> Attempt Timeout (5. cap individual attempt time)
--> HTTP call
```text
### Why This Order Matters
- **Rate limiter first**: prevents retry storms from overwhelming downstream services
- **Total timeout wraps retry**: ensures the entire operation (including all retries) has a deadline
- **Retry wraps circuit breaker**: retries can try again after the breaker resets; a broken circuit counts as a retriable failure
- **Circuit breaker wraps attempt timeout**: timed-out attempts count toward the breaker's failure threshold
- **Attempt timeout innermost**: each individual HTTP call has its own deadline
### Standard Pipeline with Defaults
```csharp
builder.Services
.AddHttpClient("catalog-api", client =>
{
client.BaseAddress = new Uri("https://catalog.internal");
})
.AddStandardResilienceHandler();
```text
This applies the standard pipeline with sensible defaults:
- **Rate limiter**: 1000 concurrent requests
- **Total timeout**: 30 seconds
- **Retry**: 3 attempts, exponential backoff (2s base), jitter
- **Circuit breaker**: 10% failure ratio, 100 sample size, 5s break duration
- **Attempt timeout**: 10 seconds
### Standard Pipeline with Custom Options
```csharp
builder.Services
.AddHttpClient("catalog-api", client =>
{
client.BaseAddress = new Uri("https://catalog.internal");
})
.AddStandardResilienceHandler(options =>
{
// Total timeout for the entire operation including retries
options.TotalRequestTimeout.Timeout = TimeSpan.FromSeconds(60);
// Retry strategy
options.Retry.MaxRetryAttempts = 5;
options.Retry.Delay = TimeSpan.FromSeconds(1);
options.Retry.BackoffType = DelayBackoffType.Exponential;
options.Retry.UseJitter = true;
options.Retry.ShouldHandle = args => ValueTask.FromResult(
args.Outcome.Result?.StatusCode is
HttpStatusCode.RequestTimeout or
HttpStatusCode.TooManyRequests or
>= HttpStatusCode.InternalServerError);
// Circuit breaker
options.CircuitBreaker.SamplingDuration = TimeSpan.FromSeconds(30);
options.CircuitBreaker.FailureRatio = 0.1;
options.CircuitBreaker.MinimumThroughput = 20;
options.CircuitBreaker.BreakDuration = TimeSpan.FromSeconds(10);
// Per-attempt timeout
options.AttemptTimeout.Timeout = TimeSpan.FromSeconds(5);
});
```text
### Configuration via appsettings.json
Bind resilience options from configuration for environment-specific tuning:
```csharp
builder.Services
.AddHttpClient("catalog-api", client =>
{
client.BaseAddress = new Uri("https://catalog.internal");
})
.AddStandardResilienceHandler(options =>
{
builder.Configuration
.GetSection("Resilience:CatalogApi")
.Bind(options);
});
```text
```json
{
"Resilience": {
"CatalogApi": {
"Retry": {
"MaxRetryAttempts": 5,
"Delay": "00:00:02",
"BackoffType": "Exponential"
},
"CircuitBreaker": {
"BreakDuration": "00:00:15"
},
"TotalRequestTimeout": {
"Timeout": "00:01:00"
}
}
}
}
```text
---
## Custom Resilience Pipelines
When the standard pipeline does not fit, build custom pipelines with Polly v8 directly.
### Retry Strategy
```csharp
builder.Services.AddResiliencePipeline("db-retry", pipelineBuilder =>
{
pipelineBuilder.AddRetry(new RetryStrategyOptions
{
MaxRetryAttempts = 3,
Delay = TimeSpan.FromMilliseconds(500),
BackoffType = DelayBackoffType.Exponential,
UseJitter = true,
ShouldHandle = new PredicateBuilder()
.Handle<DbUpdateConcurrencyException>()
.Handle<TimeoutException>(),
OnRetry = args =>
{
// Structured logging of retry attempts
var logger = args.Context.Properties
.GetValue(new ResiliencePropertyKey<ILogger>("logger"), null!);
logger?.LogWarning(
args.Outcome.Exception,
"Retry attempt {AttemptNumber} after {Delay}ms",
args.AttemptNumber,
args.RetryDelay.TotalMilliseconds);
return ValueTask.CompletedTask;
}
});
});
// Inject and use
public sealed class OrderRepository(
[FromKeyedServices("db-retry")] ResiliencePipeline pipeline,
AppDbContext db)
{
public async Task<Order> UpdateAsync(Order order, CancellationToken ct)
{
return await pipeline.ExecuteAsync(async token =>
{
db.Orders.Update(order);
await db.SaveChangesAsync(token);
return order;
}, ct);
}
}
```text
### Circuit Breaker Strategy
```csharp
builder.Services.AddResiliencePipeline("payment-gateway", pipelineBuilder =>
{
pipelineBuilder.AddCircuitBreaker(new CircuitBreakerStrategyOptions
{
SamplingDuration = TimeSpan.FromSeconds(30),
FailureRatio = 0.25, // Open after 25% failure rate
MinimumThroughput = 10, // Need at least 10 calls to evaluate
BreakDuration = TimeSpan.FromSeconds(15),
ShouldHandle = new PredicateBuilder()
.Handle<HttpRequestException>()
.Handle<TimeoutException>()
});
});
```text
### Timeout Strategy
```csharp
builder.Services.AddResiliencePipeline("external-api", pipelineBuilder =>
{
// Total timeout for the entire pipeline execution
pipelineBuilder.AddTimeout(new TimeoutStrategyOptions
{
Timeout = TimeSpan.FromSeconds(30),
OnTimeout = args =>
{
// Log timeout details for diagnostics
return ValueTask.CompletedTask;
}
});
});
```text
### Composing Multiple Strategies
Build a composite pipeline by chaining strategies. Order matters -- outermost strategy is added first:
```csharp
builder.Services.AddResiliencePipeline("composed", pipelineBuilder =>
{
// 1. Total timeout (outermost -- caps entire operation)
pipelineBuilder.AddTimeout(new TimeoutStrategyOptions
{
Timeout = TimeSpan.FromSeconds(45)
});
// 2. Retry (retries on transient failures)
pipelineBuilder.AddRetry(new RetryStrategyOptions
{
MaxRetryAttempts = 3,
Delay = TimeSpan.FromSeconds(1),
BackoffType = DelayBackoffType.Exponential,
UseJitter = true,
ShouldHandle = new PredicateBuilder()
.Handle<HttpRequestException>()
.Handle<TimeoutException>()
});
// 3. Circuit breaker (stops calling failing services)
pipelineBuilder.AddCircuitBreaker(new CircuitBreakerStrategyOptions
{
FailureRatio = 0.1,
MinimumThroughput = 20,
SamplingDuration = TimeSpan.FromSeconds(30),
BreakDuration = TimeSpan.FromSeconds(10),
ShouldHandle = new PredicateBuilder()
.Handle<HttpRequestException>()
.Handle<TimeoutException>()
});
// 4. Attempt timeout (innermost -- caps single attempt)
pipelineBuilder.AddTimeout(new TimeoutStrategyOptions
{
Timeout = TimeSpan.FromSeconds(10)
});
});
```text
---
## Typed Resilience Pipelines
For result-bearing operations, use `ResiliencePipeline<T>`:
```csharp
builder.Services.AddResiliencePipeline<string, HttpResponseMessage>(
"typed-http",
pipelineBuilder =>
{
pipelineBuilder.AddRetry(new RetryStrategyOptions<HttpResponseMessage>
{
MaxRetryAttempts = 3,
Delay = TimeSpan.FromSeconds(1),
BackoffType = DelayBackoffType.Exponential,
ShouldHandle = new PredicateBuilder<HttpResponseMessage>()
.Handle<HttpRequestException>()
.HandleResult(r => r.StatusCode >= HttpStatusCode.InternalServerError)
});
});
```text
---
## Hedging Strategy
Send parallel requests to reduce tail latency. The hedging strategy dispatches additional attempts if the initial request is slow:
```csharp
builder.Services
.AddHttpClient("search-api")
.AddStandardHedgingHandler(options =>
{
options.Hedging.MaxHedgedAttempts = 2;
options.Hedging.Delay = TimeSpan.FromMilliseconds(500);
// Hedging sends a parallel request if the first hasn't
// responded within 500ms
});
```text
**Use hedging when:**
- Operations are idempotent (GET requests, read-only queries)
- Tail latency reduction matters more than extra load
**Do not use hedging when:**
- Operations have side effects (POST, PUT, DELETE)
- Downstream services cannot handle increased load
---
## Telemetry and Observability
Polly v8 emits metrics and traces via `System.Diagnostics` out of the box when using the DI integration.
### Built-in Metrics
The `Microsoft.Extensions.Resilience` package automatically reports:
| Metric | Description |
|--------|-------------|
| `polly.strategy.attempt.duration` | Duration of each attempt |
| `polly.strategy.pipeline.duration` | Duration of the entire pipeline execution |
| `polly.strategy.attempt.count` | Count of attempts (including retries) |
These integrate with OpenTelemetry automatically when the OpenTelemetry SDK is configured in your application -- see [skill:dotnet-observability] for collector setup.
### Enabling Telemetry
Resilience telemetry is enabled automatically when using the DI-based registration (`AddResiliencePipeline`, `AddStandardResilienceHandler`). The `Microsoft.Extensions.Resilience` package registers a `MeteringEnricher` and `LoggingEnricher` that emit structured logs and metrics through the standard `ILoggerFactory` and `IMeterFactory` from DI:
```csharp
// Telemetry is automatic -- no extra configuration needed.
// Structured logs appear via ILogger; metrics via IMeter.
builder.Services
.AddHttpClient("catalog-api")
.AddStandardResilienceHandler();
// To see resilience logs, set the Polly category to Information:
// appsettings.json
// {
// "Logging": {
// "LogLevel": {
// "Polly": "Information"
// }
// }
// }
```text
---
## Migrating from Microsoft.Extensions.Http.Polly
If upgrading from the superseded `Microsoft.Extensions.Http.Polly` package:
### Before (Legacy)
```csharp
// Using Microsoft.Extensions.Http.Polly (superseded)
builder.Services
.AddHttpClient("catalog-api")
.AddTransientHttpErrorPolicy(p =>
p.WaitAndRetryAsync(3, attempt =>
TimeSpan.FromSeconds(Math.Pow(2, attempt))))
.AddTransientHttpErrorPolicy(p =>
p.CircuitBreakerAsync(5, TimeSpan.FromSeconds(30)));
```text
### After (Modern)
```csharp
// Using Microsoft.Extensions.Http.Resilience (current)
builder.Services
.AddHttpClient("catalog-api")
.AddStandardResilienceHandler(options =>
{
options.Retry.MaxRetryAttempts = 3;
options.Retry.Delay = TimeSpan.FromSeconds(2);
options.Retry.BackoffType = DelayBackoffType.Exponential;
options.CircuitBreaker.MinimumThroughput = 5;
options.CircuitBreaker.BreakDuration = TimeSpan.FromSeconds(30);
});
```text
### Migration Steps
1. Replace `Microsoft.Extensions.Http.Polly` NuGet reference with `Microsoft.Extensions.Http.Resilience`
2. Replace `AddTransientHttpErrorPolicy` calls with `AddStandardResilienceHandler` or custom pipeline
3. Translate Polly v7 policy configuration to v8 strategy options
4. Remove explicit `IAsyncPolicy<HttpResponseMessage>` type references
5. Verify retry/circuit breaker behavior matches previous configuration
---
## Key Principles
- **Use the standard pipeline for HTTP** -- `AddStandardResilienceHandler()` covers the most common case with battle-tested defaults
- **Customize via options, not custom code** -- the standard handler options cover retry count, backoff, circuit breaker thresholds, and timeouts
- **Use `AddResiliencePipeline` for non-HTTP** -- database calls, message queues, file I/O
- **Always add jitter to retries** -- prevents thundering herd when multiple clients retry simultaneously
- **Configure via appsettings.json** -- different environments need different thresholds; avoid hardcoded values in production
- **Do not suppress `TimeoutRejectedException`** -- let it propagate through the pipeline so outer strategies (retry, circuit breaker) can react
- **Do not use `Microsoft.Extensions.Http.Polly`** for new projects -- it wraps Polly v7 and is superseded
---
## Agent Gotchas
1. **Do not mix Polly v7 and v8 APIs** -- v8 uses `ResiliencePipeline` and strategy options; v7 uses `IAsyncPolicy`. They are not interchangeable.
2. **Do not add `AddStandardResilienceHandler` twice** -- it composes a full pipeline; adding it twice doubles every strategy layer.
3. **Do not set attempt timeout higher than total timeout** -- the attempt timeout must be shorter than the total timeout or it has no effect.
4. **Do not retry non-idempotent operations** -- only retry operations that are safe to repeat (GETs, idempotent writes with idempotency keys).
5. **Do not use hardcoded retry delays in production** -- always use `UseJitter = true` and configure delays via appsettings.
---
## References
- [Polly v8 documentation](https://www.pollydocs.org/)
- [Microsoft.Extensions.Http.Resilience](https://learn.microsoft.com/en-us/dotnet/core/resilience/http-resilience)
- [Microsoft.Extensions.Resilience](https://learn.microsoft.com/en-us/dotnet/core/resilience/)
- [Migration from Http.Polly to Http.Resilience](https://learn.microsoft.com/en-us/dotnet/fundamentals/networking/resilience/migration-guide)
- [Standard resilience pipeline](https://learn.microsoft.com/en-us/dotnet/core/resilience/http-resilience#standard-resilience-handler)
- [Polly v8 strategy options](https://www.pollydocs.org/strategies/)
Primary approach: Use Serena symbol operations for efficient code navigation:
serena_find_symbol instead of text searchserena_get_symbols_overview for file organizationserena_find_referencing_symbols for impact analysisserena_replace_symbol_body for clean modificationsWhen to use Serena vs traditional tools:
Example workflow:
# Instead of:
Read: src/Services/OrderService.cs
Grep: "public void ProcessOrder"
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serena_find_symbol: "OrderService/ProcessOrder"
serena_get_symbols_overview: "src/Services/OrderService.cs"