client: emit optional telemetry from prerun and prestart hooks.

[jrasell]

Description

The Nomad client can now optionally emit telemetry data from the prerun and prestart hooks. This allows operators to monitor and alert on failures and time taken to complete.

The new datapoints are:

• nomad.client.alloc_hook.prerun.success (counter)

• nomad.client.alloc_hook.prerun.failed (counter)

• nomad.client.alloc_hook.prerun.elapsed (sample)

• nomad.client.task_hook.prestart.success (counter)

• nomad.client.task_hook.prestart.failed (counter)

• nomad.client.task_hook.prestart.elapsed (sample)

The hook execution time is useful to Nomad engineering and will help optimize code where possible and understand job specification impacts on hook performance.

Currently only the PreRun and PreStart hooks have telemetry enabled, so we limit the number of new metrics being produced.

Testing & Reproduction steps

I tested on a Debian 12 arm64 using a single agent in server/client mode with this configuration.

1. Run the Nomad agent.
2. Run the promana monitoring job
3. Register the sleep batch parameterised job
4. Run a loop to continually dispatch the job while true; do; nomad job dispatch sleep; sleep 2; done to generate metrics
5. Navigate Prometheus and Grafana to look at the metrics generated

promana monitoring job spec:

job "promana" {
  group "promana" {
    network {
      mode = "bridge"
      port "prometheus" {
        to = 9090
      }
      port "grafana" {
        to = 3000
      }
    }

    service {
      name     = "prometheus-server"
      port     = "prometheus"
      provider = "nomad"
    }
    service {
      name     = "grafana-server"
      port     = "grafana"
      provider = "nomad"
    }

    task "prometheus" {
      driver = "docker"
      config {
        image = "prom/prometheus:v3.0.0"
        ports = ["prometheus"]
        args  = [
          "--config.file=${NOMAD_TASK_DIR}/config/prometheus.yml",
          "--storage.tsdb.path=/prometheus",
          "--web.listen-address=0.0.0.0:9090",
          "--web.console.libraries=/usr/share/prometheus/console_libraries",
          "--web.console.templates=/usr/share/prometheus/consoles",
        ]

        volumes = [
          "local/config:/etc/prometheus/config",
        ]
      }

      template {
        data = <<EOH
---
global:
  scrape_interval:     1s
  evaluation_interval: 1s

scrape_configs:
  - job_name: "nomad"
    metrics_path: "/v1/metrics"
    scheme: "http"
    params:
      format:
        - "prometheus"
    static_configs:
      - targets:
        - {{ env "attr.unique.network.ip-address" }}:4646
EOH

        change_mode   = "signal"
        change_signal = "SIGHUP"
        destination   = "local/config/prometheus.yml"
      }

      resources {
        cpu    = 500
        memory = 512
      }
    }

    task "grafana" {
      driver = "docker"

      config {
        image   = "grafana/grafana:11.3.1"
        volumes = [
          "local/datasources:/etc/grafana/provisioning/datasources",
        ]
      }

      template {
        data = <<EOH
apiVersion: 1
datasources:
- name: Prometheus
  type: prometheus
  access: proxy
  url: http://0.0.0.0:9090
  isDefault: true
  version: 1
  editable: false
EOH

        destination = "local/datasources/datasources.yaml"
      }

      resources {
        cpu    = 200
        memory = 256
      }
    }
  }
}

sleep job spec:

job "sleep" {
  type = "batch"
  parameterized {}
  group "sleep" {
    network {
      mode = "bridge"
    }
    task "sleep" {
      driver = "docker"
      config {
        image = "busybox"
        args  = [
          "sleep",
          "5s",
        ]
      }
      resources {
        cpu    = 50
        memory = 78 
      }
    }
  }
}

Links

Jira: https://hashicorp.atlassian.net/browse/NET-11237
RFC: https://go.hashi.co/rfc/nmd-206

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