PollyManagement

Pollymanagement is a simple library to manage your Polly CircuitBreaker policies and to provide insight in their state.

Basic usage

PollyManagement.PolicyManager.CircuitBreakerManager can be used to register all of the CircuitBreaker policies that you use within your application. First, register the CircuitBreakerManager in your DI container. Once added to the container, you can add policies to the CircuitBreakerManager by calling TryAdd<TPolicy>(string key, TPolicy policy): key is a unique identifier for the policy which can be used to retrieve the policy in places where you need it. To retrieve a policy, call TryGet(string key).

PollyManagement.ServiceCollection.CircuitBreakerManagerExtensions contains some helper methods to register the CircuitBreakerManager and policies for usage with Microsoft.Extensions.DependencyInjection.

Advanced usage

For more information about how CircuitBreakers work, see the Polly Wiki on CircuitBreakers.

Get state of a CircuitBreaker

When you want to know whether an external API is reachable, you can use the CircuitBreakerManager to get some details on the state of the CircuitBreaker. First, add your policy to the CircuitBreakerManager as described in the Basic Usage section. To get the status, for example in a healthcheck, you can use GetCircuitState(string key) where key is the identifier of the policy. You can also get the last exception handled by the policy. Use GetLastException(string key) to do so.

Manually "reset" a CircuitBreaker

Sometimes you don't want to wait on a CircuitBreaker to reset. For example, when you are certain that an external API is reachable again. In those cases, you can use the CircuitBreakerManager to manually set the state to Closed. To do so, use TryReset(string key).

Examples

PollyManagement.Webapplication contains some examples of how CircuitBreakers should (and should not) be used:

• WrongController explains the way you shoudn't use CircuitBreakers;
• BetterController uses the same approach as WrongController but with the use of the CircuitBreakerManager. Making it less prone to subtle errors.
• IdealController shows the ideal way to register your CircuitBreakers (i.e. not within a controller).
• ManagementController shows how the CircuitBreakerManager can be used to show the state of your CircuitBreakers and explains why BetterController isn't ideal.
• Startup.ConfigureServices(IServiceCollection services) shows how a CircuitBreaker policy can be registered at the start of an application using the PollyManagement.ServiceCollection.CircuitBreakerManagerExtensions.