# Stream Health

Monitor event stream availability and health status.

## Overview

Stream health monitoring detects issues with event streams:
- Stream availability
- Write/read performance
- Error rates
- Stream growth rate

## Implementation

```csharp
public interface IStreamHealthService
{
    Task<StreamHealthResult> CheckStreamHealthAsync(string streamName, CancellationToken ct = default);
    Task<StreamHealthSummary> CheckAllStreamsAsync(CancellationToken ct = default);
}

public class StreamHealthService : IStreamHealthService
{
    private readonly IEventStreamStore _eventStore;
    private readonly ILogger<StreamHealthService> _logger;

    public async Task<StreamHealthResult> CheckStreamHealthAsync(
        string streamName,
        CancellationToken ct)
    {
        var result = new StreamHealthResult { StreamName = streamName };

        try
        {
            // Check stream exists and is accessible
            var streamHead = await _eventStore.GetStreamHeadAsync(streamName, ct);
            result.IsAccessible = true;
            result.CurrentOffset = streamHead;

            // Check error rate
            var errorRate = await GetErrorRateAsync(streamName, ct);
            result.ErrorRate = errorRate;

            // Determine health status
            result.Status = errorRate switch
            {
                > 10 => HealthStatus.Unhealthy,
                > 5 => HealthStatus.Degraded,
                _ => HealthStatus.Healthy
            };

            result.Message = $"Stream healthy (offset: {streamHead}, error rate: {errorRate}/min)";
        }
        catch (StreamNotFoundException)
        {
            result.Status = HealthStatus.Unhealthy;
            result.Message = "Stream not found";
        }
        catch (Exception ex)
        {
            result.Status = HealthStatus.Unhealthy;
            result.Message = $"Stream check failed: {ex.Message}";
            _logger.LogError(ex, "Error checking stream health for {StreamName}", streamName);
        }

        return result;
    }
}
```

## See Also

- [Health Checks Overview](README.md)
- [Consumer Health](consumer-health.md)