Mermin Application Metrics

This guide describes the Prometheus metrics endpoint exposed by Mermin and provides a comprehensive breakdown of all available metrics, their types, and descriptions. See the metrics configuration document for more details on metrics configuration.

Metrics Endpoint

Mermin exposes Prometheus metrics in the standard Prometheus text format at multiple HTTP endpoints:

• /metrics - All metrics (standard + debug if enabled)

• /metrics/standard - Standard metrics only (no high-cardinality labels)

• /metrics/debug - Debug metrics only (returns 404 if disabled)

• /metrics:summary - JSON summary of all available metrics with metadata (name, type, description, labels, category)

Standard vs Debug Metrics:

• Standard metrics: Always enabled, aggregated across resources, safe for production.

• Debug metrics: High-cardinality labels (per-interface, per-resource), must be explicitly enabled via metrics.debug_metrics_enabled = true.

Metrics Reference

All metrics follow the naming convention: mermin_<subsystem>_<name>. Metrics are categorized into logical subsystems that correspond to different components of Mermin:

• ebpf: For eBPF-specific metrics

• channel: Internal Mermin channels metrics

• export: Export-related metrics

• flow: Metrics on the Flow Spans

• interface: Network interface-related metrics

• k8s: For Kubernetes watcher metrics

• taskmanager: Internal Mermin tasks metrics

eBPF Metrics (mermin_ebpf_*)

This section describes metrics from the eBPF layer, responsible for capturing low-level packets. These metrics provide visibility into the status of loaded eBPF programs and the usage of eBPF maps. Monitoring these is crucial for ensuring that Mermin's foundational data collection mechanism functions as expected.

• mermin_ebpf_bpf_fs_writable Type: gauge Description: Whether /sys/fs/bpf is writable for TCX link pinning (1 = writable, 0 = not writable)

• mermin_ebpf_map_bytes_total Type: counter Description: Total bytes processed through eBPF maps and ring buffers Labels:

  • map

• mermin_ebpf_map_capacity Type: gauge Description: Maximum capacity of eBPF maps. For hash maps (FLOW_STATS, LISTENING_PORTS) this is max entries. For ring buffers (FLOW_EVENTS) this is size in bytes. Labels:

  • map

• mermin_ebpf_map_entries Type: gauge Description: Current number of entries in eBPF maps. For hash maps (FLOW_STATS, LISTENING_PORTS) this is the entry count. Not available for ring buffers (FLOW_EVENTS). Labels:

  • map

• mermin_ebpf_map_ops_total Type: counter Description: Total number of eBPF map operations Labels:

  • map

  • operation

  • status

• mermin_ebpf_method Type: gauge Description: Current eBPF attachment method used (tc or tcx) Labels:

  • attachment

Network Interface Metrics (mermin_interface_*)

These metrics provide visibility into network traffic processed by Mermin across all monitored interfaces. They are essential for understanding the overall throughput and packet rates processed by Mermin.

• mermin_interface_bytes_total Type: counter Description: Total number of bytes processed across all interfaces

• mermin_interface_packets_total Type: counter Description: Total number of packets processed across all interfaces

Flow Metrics (mermin_flow_*)

• mermin_flow_spans_active_total Type: gauge Description: Current number of active flow traces across all interfaces

• mermin_flow_spans_created_total Type: counter Description: Total number of flow spans created across all interfaces

Kubernetes Watcher Metrics (mermin_k8s_watcher_*)

These metrics track events and performance of the Kubernetes resource watchers used by Mermin for metadata enrichment and resource monitoring.

• mermin_k8s_watcher_events_total Type: counter Description: Total number of K8s kind watcher events (aggregated across resources) Labels:

  • event

  • kind

• mermin_k8s_watcher_ip_index_update_duration_seconds Type: histogram Description: Duration of K8s IP index updates

Kubernetes Decorator Metrics (mermin_k8s_decorator_*)

These metrics exposes the details to the Kubernetes decorator stage.

• mermin_k8s_decorator_flow_spans_total Type: counter Description: Total number of flow spans processed by the K8s decorator Labels:

  • status

Flow Span Export Metrics (mermin_export_*)

These metrics track the export of flow spans from Mermin to external systems (such as OTLP collectors), providing insight into export performance and reliability.

• mermin_export_batch_size Type: histogram Description: Number of spans per export batch

• mermin_export_flow_spans_total Type: counter Description: Total number of flow spans exported to external systems Labels:

  • exporter

  • status

Channel Metrics (mermin_channel_*)

These metrics offer insight into the internal channels used for data transmission.

• mermin_channel_capacity Type: gauge Description: Capacity of internal channels Labels:

  • channel

• mermin_channel_entries Type: gauge Description: Current number of items in channels Labels:

  • channel

• mermin_channel_sends_total Type: counter Description: Total number of send operations to internal channels Labels:

  • channel

  • status

Pipeline Metrics (mermin_pipeline_*)

These metrics offer insight into the internal pipelines used for data mutation (flow generation, decoration).

• mermin_pipeline_duration_seconds Type: histogram Description: Processing duration by pipeline stage Labels:

  • stage

TaskManager Metrics (mermin_taskmanager_*)

These metrics track the number and type of active background tasks managed by Mermin.

• mermin_taskmanager_tasks_active Type: gauge Description: Current number of active tasks across all task types Labels:

  • task