Prognosis.Reactive 5.0.0

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

All extensions operate on HealthGraph. Use HealthGraph.Create(root) to materialize the graph, then chain Rx operators.

PollHealthReport — timer-driven polling

Polls on a fixed interval, re-evaluates every node, and emits a HealthReport whenever the graph state changes:

using Prognosis.Reactive;

var graph = HealthGraph.Create(app);
graph.PollHealthReport(TimeSpan.FromSeconds(30))
    .Subscribe(report =>
        Console.WriteLine($"{report.Nodes.Count} nodes"));

ObserveHealthReport — push-triggered evaluation

Reacts to HealthGraph.StatusChanged events and produces a fresh report immediately — no polling delay. Changes in any transitive dependency bubble up automatically.

graph.ObserveHealthReport()
    .Subscribe(report =>
        Console.WriteLine($"{report.Nodes.Count} nodes"));

SelectHealthChanges — diff-based change stream

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

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

Each StatusChange includes the service name, previous status, current status, and optional reason — derived from HealthReport.DiffTo in the core library.

Sharing streams across subscribers

The Rx helpers produce cold IObservable<HealthReport> streams — each subscription runs an independent pipeline and triggers its own evaluations. To share a single evaluation across multiple subscribers:

var shared = graph.CreateSharedReportStream(TimeSpan.FromSeconds(30));
var shared = graph.CreateSharedObserveStream();

// With replay for late subscribers:
var shared = graph.CreateSharedReportStream(TimeSpan.FromSeconds(30),
    ShareStrategy.ReplayLatest);

Or use standard Rx multicast operators directly: Publish().RefCount() or Replay(1).RefCount().

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+)