Monitoring & Observability

Effective monitoring is critical for maintaining voice agent quality in production. Track latency, errors, and conversation quality in real-time.

Key Metrics

Latency Metrics

Quality Metrics

Volume Metrics

Implementation

Metrics Collection

type MetricsCollector struct {
    prometheus *prometheus.Registry
    statsd     *statsd.Client
}

// Latency metrics
var (
    e2eLatency = prometheus.NewHistogramVec(
        prometheus.HistogramOpts{
            Name:    "voice_agent_e2e_latency_ms",
            Help:    "End-to-end response latency",
            Buckets: []float64{100, 200, 300, 500, 750, 1000, 1500, 2000},
        },
        []string{"agent_id", "language"},
    )

    sttLatency = prometheus.NewHistogram(
        prometheus.HistogramOpts{
            Name:    "voice_agent_stt_latency_ms",
            Help:    "STT processing latency",
            Buckets: []float64{50, 100, 150, 200, 300, 500},
        },
    )

    llmLatency = prometheus.NewHistogramVec(
        prometheus.HistogramOpts{
            Name:    "voice_agent_llm_ttft_ms",
            Help:    "LLM time to first token",
            Buckets: []float64{50, 100, 150, 200, 300, 400, 500},
        },
        []string{"provider", "model"},
    )
)

func (m *MetricsCollector) RecordE2ELatency(agentID, language string, latency time.Duration) {
    e2eLatency.WithLabelValues(agentID, language).Observe(float64(latency.Milliseconds()))
}

Structured Logging

type CallLogger struct {
    logger *zap.Logger
}

func (l *CallLogger) LogCallStart(call *Call) {
    l.logger.Info("call_started",
        zap.String("call_id", call.ID),
        zap.String("agent_id", call.AgentID),
        zap.String("caller", call.CallerNumber),
        zap.String("language", call.Language),
        zap.Time("start_time", call.StartTime),
    )
}

func (l *CallLogger) LogTurn(turn *ConversationTurn) {
    l.logger.Info("conversation_turn",
        zap.String("call_id", turn.CallID),
        zap.String("role", turn.Role),
        zap.String("transcript", turn.Text),
        zap.Duration("stt_latency", turn.STTLatency),
        zap.Duration("llm_latency", turn.LLMLatency),
        zap.Duration("tts_latency", turn.TTSLatency),
        zap.Duration("e2e_latency", turn.E2ELatency),
        zap.Bool("interrupted", turn.WasInterrupted),
    )
}

func (l *CallLogger) LogCallEnd(call *Call) {
    l.logger.Info("call_ended",
        zap.String("call_id", call.ID),
        zap.Duration("duration", call.Duration),
        zap.Int("turn_count", call.TurnCount),
        zap.Bool("transferred", call.WasTransferred),
        zap.String("end_reason", call.EndReason),
    )
}

Distributed Tracing

import (
    "go.opentelemetry.io/otel"
    "go.opentelemetry.io/otel/trace"
)

type TracedPipeline struct {
    tracer trace.Tracer
}

func (p *TracedPipeline) ProcessTurn(ctx context.Context, audio []byte) (string, error) {
    ctx, span := p.tracer.Start(ctx, "voice_agent.process_turn")
    defer span.End()

    // STT span
    ctx, sttSpan := p.tracer.Start(ctx, "stt.transcribe")
    transcript, err := p.stt.Transcribe(ctx, audio)
    sttSpan.SetAttributes(
        attribute.String("transcript", transcript),
        attribute.Bool("error", err != nil),
    )
    sttSpan.End()

    // LLM span
    ctx, llmSpan := p.tracer.Start(ctx, "llm.generate")
    response, err := p.llm.Generate(ctx, transcript)
    llmSpan.SetAttributes(
        attribute.Int("tokens", response.TokenCount),
        attribute.String("model", p.llmModel),
    )
    llmSpan.End()

    // TTS span
    ctx, ttsSpan := p.tracer.Start(ctx, "tts.synthesize")
    _, err = p.tts.Synthesize(ctx, response.Text)
    ttsSpan.SetAttributes(
        attribute.Int("audio_length_ms", response.AudioLengthMs),
    )
    ttsSpan.End()

    return response.Text, nil
}

Dashboards

Call Volume Dashboard

┌─────────────────────────────────────────────────────────────────────┐
│                      Call Volume - Last 24h                          │
│                                                                       │
│  Calls/Hour                                                          │
│   500 ┤                              ╭──╮                            │
│   400 ┤                          ╭───╯  ╰──╮                         │
│   300 ┤                      ╭───╯          ╰──╮                     │
│   200 ┤              ╭───────╯                  ╰──╮                 │
│   100 ┤      ╭───────╯                              ╰───────╮        │
│     0 ┼──────╯                                              ╰─────── │
│       └───────┬───────┬───────┬───────┬───────┬───────┬─────────────┤
│              00:00   04:00   08:00   12:00   16:00   20:00          │
│                                                                       │
│  Total: 8,432    Peak: 523/hr    Avg: 352/hr    Active Now: 47      │
└─────────────────────────────────────────────────────────────────────┘

Latency Dashboard

┌─────────────────────────────────────────────────────────────────────┐
│                      E2E Latency Distribution                        │
│                                                                       │
│  P50: 412ms   P90: 623ms   P99: 892ms   Target: <500ms              │
│                                                                       │
│   ██████████████████████████████░░░░░░░░░░ 412ms (p50)              │
│   ██████████████████████████████████████████████████░░ 623ms (p90)  │
│   ██████████████████████████████████████████████████████████ 892ms  │
│                                                                       │
│  By Component:                                                       │
│   VAD:  ████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░ 48ms        │
│   STT:  █████████████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░ 142ms       │
│   LLM:  ████████████████████░░░░░░░░░░░░░░░░░░░░░░░░░░░ 186ms       │
│   TTS:  █████████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░ 89ms        │
└─────────────────────────────────────────────────────────────────────┘

Error Rate Dashboard

┌─────────────────────────────────────────────────────────────────────┐
│                      Error Rates - Last 1h                           │
│                                                                       │
│  Error Type                    Count    Rate      Trend              │
│  ─────────────────────────────────────────────────────               │
│  STT Connection Failed         12       0.14%     ↓ -5%              │
│  LLM Timeout                   8        0.09%     ↑ +12%             │
│  TTS Rate Limited              3        0.04%     ↓ -50%             │
│  WebSocket Disconnected        45       0.53%     → 0%               │
│  Transfer Failed               2        0.02%     ↓ -80%             │
│                                                                       │
│  Overall Error Rate: 0.82%    Target: <1%    Status: ✅ Healthy      │
└─────────────────────────────────────────────────────────────────────┘

Alerting

Alert Configuration

# alerts.yaml
groups:
  - name: voice_agent
    rules:
      - alert: HighE2ELatency
        expr: histogram_quantile(0.95, voice_agent_e2e_latency_ms) > 1000
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "High E2E latency detected"
          description: "P95 latency is {{ $value }}ms (threshold: 1000ms)"

      - alert: HighErrorRate
        expr: rate(voice_agent_errors_total[5m]) / rate(voice_agent_calls_total[5m]) > 0.05
        for: 2m
        labels:
          severity: critical
        annotations:
          summary: "Error rate above 5%"
          description: "Current error rate: {{ $value | humanizePercentage }}"

      - alert: LowCallCompletionRate
        expr: rate(voice_agent_calls_completed[1h]) / rate(voice_agent_calls_started[1h]) < 0.90
        for: 15m
        labels:
          severity: warning
        annotations:
          summary: "Call completion rate below 90%"

      - alert: ProviderDown
        expr: up{job=~"stt|tts|llm"} == 0
        for: 1m
        labels:
          severity: critical
        annotations:
          summary: "Provider {{ $labels.job }} is down"

Alert Implementation

type AlertManager struct {
    slack      *slack.Client
    pagerduty  *pagerduty.Client
    thresholds map[string]float64
}

func (a *AlertManager) CheckMetrics(metrics *Metrics) {
    // Check latency
    if metrics.E2EP95 > a.thresholds["e2e_latency_ms"] {
        a.sendAlert(Alert{
            Severity: "warning",
            Title:    "High E2E Latency",
            Message:  fmt.Sprintf("P95 latency: %dms", metrics.E2EP95),
        })
    }

    // Check error rate
    if metrics.ErrorRate > a.thresholds["error_rate"] {
        a.sendAlert(Alert{
            Severity: "critical",
            Title:    "High Error Rate",
            Message:  fmt.Sprintf("Error rate: %.2f%%", metrics.ErrorRate*100),
        })
    }
}

func (a *AlertManager) sendAlert(alert Alert) {
    switch alert.Severity {
    case "critical":
        a.pagerduty.TriggerIncident(alert)
        a.slack.PostMessage("#alerts-critical", alert.Message)
    case "warning":
        a.slack.PostMessage("#alerts", alert.Message)
    }
}

Debugging

Call Recording and Playback

type CallRecorder struct {
    storage Storage
}

func (r *CallRecorder) RecordCall(callID string) *Recording {
    return &Recording{
        CallID:    callID,
        Audio:     []byte{},
        Events:    []Event{},
        StartTime: time.Now(),
    }
}

func (r *CallRecorder) AddAudio(recording *Recording, audio []byte, direction string) {
    recording.Audio = append(recording.Audio, audio...)
    recording.Events = append(recording.Events, Event{
        Type:      "audio",
        Direction: direction,
        Timestamp: time.Now(),
        Size:      len(audio),
    })
}

func (r *CallRecorder) Save(recording *Recording) error {
    return r.storage.SaveRecording(recording)
}

Debug Logging

type DebugLogger struct {
    enabled bool
    level   LogLevel
}

func (l *DebugLogger) LogPipelineEvent(event PipelineEvent) {
    if !l.enabled {
        return
    }

    switch event.Type {
    case "audio_received":
        l.log("audio", "Received %d bytes from caller", event.Size)

    case "vad_speech_start":
        l.log("vad", "Speech started at probability %.2f", event.Probability)

    case "stt_interim":
        l.log("stt", "Interim: %s (stability: %.2f)", event.Text, event.Stability)

    case "stt_final":
        l.log("stt", "Final: %s (latency: %dms)", event.Text, event.Latency)

    case "llm_token":
        l.log("llm", "Token: %s (TTFT: %dms)", event.Token, event.TTFT)

    case "tts_chunk":
        l.log("tts", "TTS chunk: %d bytes", event.Size)

    case "interruption":
        l.log("interrupt", "User interrupted, clearing queue")
    }
}

Health Checks

type HealthChecker struct {
    providers []Provider
}

func (h *HealthChecker) Check() HealthStatus {
    status := HealthStatus{
        Healthy:    true,
        Components: make(map[string]ComponentHealth),
    }

    // Check each provider
    for _, provider := range h.providers {
        health := h.checkProvider(provider)
        status.Components[provider.Name()] = health

        if !health.Healthy {
            status.Healthy = false
        }
    }

    return status
}

func (h *HealthChecker) checkProvider(p Provider) ComponentHealth {
    start := time.Now()
    err := p.Ping()
    latency := time.Since(start)

    return ComponentHealth{
        Healthy: err == nil,
        Latency: latency,
        Error:   err,
    }
}

// Health endpoint
func healthHandler(w http.ResponseWriter, r *http.Request) {
    status := healthChecker.Check()

    if status.Healthy {
        w.WriteHeader(http.StatusOK)
    } else {
        w.WriteHeader(http.StatusServiceUnavailable)
    }

    json.NewEncoder(w).Encode(status)
}

Next Steps

• Scaling - Handle high volume
• Error Handling - Graceful failures
• Latency Optimization - Improve performance