---

name: OpenTelemetry Instrumentation Extension description: Extend OpenTelemetry instrumentation when new functionality is added to the MCP Gateway. Use when (1) new operations/functions are added, (2) reviewing code for missing instrumentation, (3) user requests otel/telemetry additions, or (4) working with state-changing operations. Analyzes git diff, suggests instrumentation points following project standards in docs/telemetry/README.md, implements with approval, writes tests, updates documentation, and verifies with debug logging and docker logs.

OpenTelemetry Instrumentation Extension

Automatically extend OpenTelemetry instrumentation for new functionality in the MCP Gateway, following established patterns documented in docs/telemetry/README.md.

When to Use This Skill

Automatically apply when:

• New state-changing operations added (Create, Update, Delete, Push, Pull, Add, Remove, etc.)
• New CLI commands added to cmd/docker-mcp/
• New packages with operations in pkg/
• User mentions "otel", "telemetry", "instrumentation", "metrics", or "tracing"
• Code changes that modify state (database, files, containers, configuration)
• Reviewing code for telemetry coverage

Workflow

Phase 1: Analysis & Suggestion

1. Read project telemetry standards:

   • Read docs/telemetry/README.md "Development Guidelines" section
   • Read pkg/telemetry/telemetry.go to understand existing patterns and metrics

2. Identify scope using git diff:

   • Find new/changed files in pkg/ and cmd/docker-mcp/
   • Identify functions performing state-changing operations
   • Infer domain from package structure (e.g., pkg/foo/ → domain: foo)

3. Categorize findings:

   • Operations in existing domains (use existing metrics)
   • Operations in new domains (need new metrics)

4. Present suggestions to user:

   • List each function needing instrumentation with file:line reference
   • Specify operation type (create, update, delete, etc.)
   • Identify domain and whether metrics exist
   • Show what will be added (instrumentation code, metrics, docs, tests)

Phase 2: Implementation (After User Approval)

Execute in this order:

1. Make changes: Instrument operations and add metrics to pkg/telemetry/telemetry.go
2. Verify: Build, run with OTEL collector, check docker logs otel-debug output
3. Write tests: Add tests to pkg/telemetry/telemetry_test.go
4. Update docs: Add metrics/operations to docs/telemetry/README.md
5. Run tests: Execute make test
6. Final verification: Run ./docs/telemetry/testing/test-telemetry.sh

Key Principles

Follow the project's documented guidelines from docs/telemetry/README.md:

1. Use Existing Providers: Get global tracer/meter from OTEL
2. Preserve Server Lineage: Include server attribution in all telemetry
3. Non-Blocking Operations: Telemetry never blocks or fails operations
4. Debug Support: Add logging behind DOCKER_MCP_TELEMETRY_DEBUG
5. Follow Naming Conventions: Use mcp.<domain>.<field> pattern
6. Deferred Success Tracking: Only set success on clean completion

Where to Find Information

ALWAYS read these files before suggesting changes:

1. docs/telemetry/README.md - Source of truth for:

   • Development guidelines (lines 419-474)
   • Existing metrics and attributes
   • Testing procedures
   • Naming conventions

2. pkg/telemetry/telemetry.go - Understand:

   • Existing metric instruments
   • Recording function patterns
   • Helper functions for spans
   • Init() structure

3. pkg/telemetry/telemetry_test.go - See:

   • Testing patterns
   • How to verify metrics

Instrumentation Pattern

Use the simple defer pattern from cmd/docker-mcp/catalog/create.go:

Copyfunc OperationName(ctx context.Context, identifier string, ...) error {
    telemetry.Init()
    start := time.Now()
    var success bool
    defer func() {
        duration := time.Since(start)
        telemetry.Record<Domain>Operation(ctx, "operation_name", identifier,
            float64(duration.Milliseconds()), success)
    }()

    // ... operation logic ...

    // Optional: Record resource counts
    telemetry.Record<Domain><Resources>(ctx, identifier, int64(count))

    success = true
    return nil
}

Note: If identifier is generated during execution, the defer captures its final value.

Adding New Domains

When instrumentation is needed for a new domain (e.g., new package pkg/newdomain/):

1. Add Metric Instruments in pkg/telemetry/telemetry.go

In the Init() function, add global variables and create metric instruments:

Copyvar (
    // ... existing metrics ...

    // New domain metrics
    newdomainOperations        metric.Int64Counter
    newdomainOperationDuration metric.Float64Histogram
    newdomainResources         metric.Int64Gauge  // If managing resources
)

func Init() {
    // ... existing init code ...

    newdomainOperations, _ = meter.Int64Counter(
        "mcp.newdomain.operations",
        metric.WithDescription("New domain operations count"),
    )
    newdomainOperationDuration, _ = meter.Float64Histogram(
        "mcp.newdomain.operation.duration",
        metric.WithDescription("New domain operation duration in milliseconds"),
    )
    newdomainResources, _ = meter.Int64Gauge(
        "mcp.newdomain.resources",
        metric.WithDescription("Number of resources in new domain"),
    )
}

2. Add Recording Functions in pkg/telemetry/telemetry.go

After the Init() function, add recording functions:

Copyfunc RecordNewdomainOperation(ctx context.Context, operation, identifier string, durationMs float64, success bool) {
    if newdomainOperations == nil || newdomainOperationDuration == nil {
        return
    }
    attrs := []attribute.KeyValue{
        attribute.String("mcp.newdomain.operation", operation),
        attribute.String("mcp.newdomain.id", identifier),  // or .name, .ref as appropriate
        attribute.Bool("mcp.newdomain.success", success),
    }
    newdomainOperations.Add(ctx, 1, metric.WithAttributes(attrs...))
    newdomainOperationDuration.Record(ctx, durationMs, metric.WithAttributes(attrs...))
}

// Optional: Add resource counting function if applicable
func RecordNewdomainResources(ctx context.Context, identifier string, count int64) {
    if newdomainResources == nil {
        return
    }
    attrs := []attribute.KeyValue{
        attribute.String("mcp.newdomain.id", identifier),
    }
    newdomainResources.Record(ctx, count, metric.WithAttributes(attrs...))
}

3. Write Tests in pkg/telemetry/telemetry_test.go

Add test cases following existing patterns:

Copyfunc TestRecordNewdomainOperation(t *testing.T) {
    spanRecorder, metricReader := setupTestTelemetry(t)
    Init()
    ctx := context.Background()

    // Test successful operation
    RecordNewdomainOperation(ctx, "create", "test-id", 123.45, true)

    // Collect and verify metrics
    var rm metricdata.ResourceMetrics
    err := metricReader.Collect(ctx, &rm)
    require.NoError(t, err)

    // Find and verify the counter metric
    foundCounter := false
    foundHistogram := false
    for _, sm := range rm.ScopeMetrics {
        for _, m := range sm.Metrics {
            if m.Name == "mcp.newdomain.operations" {
                foundCounter = true
                sum := m.Data.(metricdata.Sum[int64])
                require.Len(t, sum.DataPoints, 1)
                assert.Equal(t, int64(1), sum.DataPoints[0].Value)

                // Verify attributes
                attrs := sum.DataPoints[0].Attributes
                assert.Contains(t, attrs.ToSlice(), attribute.String("mcp.newdomain.operation", "create"))
                assert.Contains(t, attrs.ToSlice(), attribute.String("mcp.newdomain.id", "test-id"))
                assert.Contains(t, attrs.ToSlice(), attribute.Bool("mcp.newdomain.success", true))
            }
            if m.Name == "mcp.newdomain.operation.duration" {
                foundHistogram = true
                histogram := m.Data.(metricdata.Histogram[float64])
                require.Len(t, histogram.DataPoints, 1)
                assert.Equal(t, float64(123.45), histogram.DataPoints[0].Sum)
            }
        }
    }

    assert.True(t, foundCounter, "Counter metric not found")
    assert.True(t, foundHistogram, "Histogram metric not found")
}

4. Update Documentation in docs/telemetry/README.md

Add a new section for the domain in the appropriate location. Follow the existing format:

Copy### New Domain Operations

Operations for managing [description of what this domain does]:
- **`mcp.newdomain.operations`** - New domain operations (create, update, delete, etc.)
- **`mcp.newdomain.operation.duration`** - Duration of new domain operations
- **`mcp.newdomain.resources`** - Gauge showing number of resources in new domain

#### New Domain Attributes
- **`mcp.newdomain.operation`** - Type of operation (create, update, delete, etc.)
- **`mcp.newdomain.id`** - ID of the resource
- **`mcp.newdomain.success`** - Boolean indicating operation success

Verification

After making changes, verify telemetry output:

Copy# Build
make docker-mcp

# Start OTEL collector
docker run --rm -d --name otel-debug \
  -p 4317:4317 -p 4318:4318 \
  -v $(pwd)/docs/telemetry/testing/otel-collector-config.yaml:/config.yaml \
  otel/opentelemetry-collector:latest --config=/config.yaml

# Run with telemetry enabled
export DOCKER_MCP_TELEMETRY_DEBUG=1
export DOCKER_CLI_OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317
docker mcp [command]

# Check collector output
docker logs otel-debug | grep "mcp.newdomain"

# Cleanup
docker stop otel-debug

Verify the output matches expectations before proceeding to write tests and docs.

Analysis Strategy

When analyzing git diff:

1. Look for operation verbs in function names:

   • Create, Add, Update, Modify, Set, Configure, Register
   • Delete, Remove, Unregister, Clear
   • Push, Pull, Export, Import, Sync
   • Start, Stop, Run, Execute

2. Look for state changes:

   • Database operations (DAO/DB calls)
   • File system operations (create, delete, write)
   • Container operations (start, stop, create, delete)
   • Configuration changes (save, update)

3. Infer domain from file path:

   • pkg/workingset/ → domain: profile
   • pkg/catalog_next/ → domain: catalog_next
   • cmd/docker-mcp/server/ → domain: server
   • Pattern: use logical grouping name

4. Check if telemetry exists:

   • Search pkg/telemetry/telemetry.go for Record<Domain> functions
   • If exists: use existing metrics
   • If not: propose new domain metrics

Implementation Checklist

Follow this sequence:

• Read patterns from docs/telemetry/README.md
• Instrument operations with simple defer pattern
• Add new metrics to pkg/telemetry/telemetry.go (if new domain)
• Verify with docker logs otel-debug - confirm output matches expectations
• Write tests in pkg/telemetry/telemetry_test.go
• Update docs/telemetry/README.md with new metrics
• Run make test - verify tests pass
• Run ./docs/telemetry/testing/test-telemetry.sh - final verification

Important Notes

• Read documentation first
• Follow existing patterns
• Ask for approval before implementing
• Verify early and often with collector logs