Prognosis.Reactive 2.1.0

Prognosis.Reactive

System.Reactive extensions for the Prognosis service health graph. Provides Rx-based alternatives to the polling-based HealthMonitor in the core package.

Installation

dotnet add package Prognosis.Reactive

API

PollHealthReport — timer-driven polling

Polls the full health graph on a fixed interval, notifying all observable services and emitting a HealthReport whenever the graph state changes:

using Prognosis.Reactive;

var roots = new IServiceHealth[] { app };

roots.PollHealthReport(TimeSpan.FromSeconds(30))
    .Subscribe(report =>
        Console.WriteLine($"Overall: {report.OverallStatus}"));

ObserveHealthReport — push-triggered evaluation

Reacts to StatusChanged events from leaf nodes (services with no dependencies), throttles to avoid evaluation storms, then runs a single-pass graph evaluation:

roots.ObserveHealthReport(TimeSpan.FromMilliseconds(500))
    .Subscribe(report =>
        Console.WriteLine($"Overall: {report.OverallStatus}"));

Only leaf nodes are observed as triggers since parent status changes are always a consequence of HealthAggregator.NotifyGraph, not exogenous events.

SelectServiceChanges — diff-based change stream

Projects consecutive HealthReport emissions into individual ServiceStatusChange events by diffing the reports. Composable with any report source:

roots.PollHealthReport(TimeSpan.FromSeconds(30))
    .SelectServiceChanges()
    .Subscribe(change =>
        Console.WriteLine($"{change.Name}: {change.Previous} → {change.Current}"));

Each ServiceStatusChange includes the service name, previous status, current status, and optional reason — derived from HealthAggregator.Diff in the core library.

Sharing patterns

The Rx helpers in this package produce cold IObservable<HealthReport> streams — each subscription runs an independent pipeline and triggers its own evaluations. To avoid duplicate work across multiple subscribers, multicast the stream with one of the common patterns:

• Auto-start while there are subscribers (stop when last unsubscribes):

var shared = roots.ObserveHealthReport(TimeSpan.FromMilliseconds(500))
    .Publish()
    .RefCount();

shared.Subscribe(...);
shared.Subscribe(...);

• Replay the latest report to late subscribers:

var shared = roots.ObserveHealthReport(TimeSpan.FromMilliseconds(500))
    .Replay(1)
    .RefCount();

shared.Subscribe(...); // immediate get latest

If you prefer a convenience helper, this package also provides CreateSharedReportStream and CreateSharedObserveStream which wrap these patterns. They are opt-in and live in Prognosis.Reactive.

Dependencies

• Prognosis (core library)
• System.Reactive >= 6.0.1

Requirements

• .NET Standard 2.0+ (.NET Framework 4.6.1+, .NET Core 2.0+, .NET 5+)