rtt-tracing.md

RTT Value Tracing and Investigation

RTT Journey Flow Diagram

graph TD
    A[Probe Service] -->|Measure RTT| B[CheckResult]
    B -->|RttMs| C[MonitoringBackgroundService]
    C -->|Update Endpoint| D[OutageDetectionService]
    D -->|Persist LastRttMs| E[StatusService]
    E -->|Serialize RTT| F[API Controller]
    F -->|Response| G[Frontend Service]
    G -->|Render| H[Frontend Components]

    subgraph Potential Failure Points
        A -->|Null/Zero RTT| B
        B -->|Null RttMs| C
        C -->|Ignore Null RTT| D
        D -->|Skip Update| E
        E -->|Empty RTT| F
        F -->|Omit RTT| G
        G -->|Display Placeholder| H
    end

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RTT Tracing Points

1. Probe Service (ProbeService.cs)

• Probe Types:
  • ICMP: Uses reply.RoundtripTime
  • TCP: Uses stopwatch.ElapsedMilliseconds
  • HTTP: Uses stopwatch.ElapsedMilliseconds
• Failure Handling:
  • Sets RttMs to null on probe failures
  • Different measurement methods may introduce inconsistencies

2. Background Monitoring Service

• Logs RTT with trace:

  _logger.LogTrace("Probed endpoint {EndpointId} ({Name}): {Status} in {RttMs}ms")

• Converts null RTT to "N/A"

3. Outage Detection Service

• Copies result.RttMs to new records
• Potential loss point if RTT is null

4. Status Service

• Uses endpoint.LastRttMs to populate status responses
• May return null/empty RTT

5. Frontend Service and Components

• Uses optional chaining and nullish coalescing
• Handles null RTT with placeholders ('-')

Investigation Steps

1. Probe Measurement Verification

• Compare RTT measurements across different probe types
• Add detailed logging in ProbeService
• Verify stopwatch and RoundtripTime calculations

2. Null Value Propagation Analysis

• Trace null RTT through each service layer
• Add comprehensive logging
• Validate null handling in serialization

3. API Contract Validation

• Inspect API response DTOs
• Check JSON serialization of RTT values
• Verify optional/nullable field handling

4. Frontend Parsing Investigation

• Review TypeScript type definitions
• Validate RTT parsing in API services
• Test display logic for various RTT scenarios

5. Comprehensive Test Scenarios

• Successful probe with non-zero RTT
• Failed probe (null RTT)
• Edge cases: zero, very low, very high RTT values
• Multiple probe type comparisons

Potential Improvement Recommendations

• Standardize RTT measurement across probe types
• Implement consistent null/zero RTT handling
• Add more granular logging and tracing
• Create comprehensive test suite for RTT propagation