167 lines
7.2 KiB
Plaintext
167 lines
7.2 KiB
Plaintext
---
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layout: docs
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page_title: Telemetry Overview
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sidebar_title: Telemetry
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description: |-
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Overview of runtime metrics available in Nomad along with monitoring and
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alerting.
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---
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# Telemetry Overview
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The Nomad client and server agents collect a wide range of runtime metrics
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related to the performance of the system. Operators can use this data to gain
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real-time visibility into their cluster and improve performance. Additionally,
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Nomad operators can set up monitoring and alerting based on these metrics in
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order to respond to any changes in the cluster state.
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On the server side, leaders and
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followers have metrics in common as well as metrics that are specific to their
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roles. Clients have separate metrics for the host metrics and for
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allocations/tasks, both of which have to be [explicitly
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enabled][telemetry-stanza]. There are also runtime metrics that are common to
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all servers and clients.
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By default, the Nomad agent collects telemetry data at a [1 second
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interval][collection-interval]. Note that Nomad supports [Gauges, counters and
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timers][metric-types].
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There are three ways to obtain metrics from Nomad:
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- Query the [/metrics API endpoint][metrics-api-endpoint] to return metrics for
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the current Nomad process (as of Nomad 0.7). This endpoint supports Prometheus
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formatted metrics.
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- Send the USR1 signal to the Nomad process. This will dump the current
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telemetry information to STDERR (on Linux).
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- Configure Nomad to automatically forward metrics to a third-party provider.
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Nomad 0.7 added support for [tagged metrics][tagged-metrics], improving the
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integrations with [DataDog][datadog-telem] and [Prometheus][prometheus-telem].
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Metrics can also be forwarded to [Statsite][statsite-telem],
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[StatsD][statsd-telem], and [Circonus][circonus-telem].
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## Alerting
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The recommended practice for alerting is to leverage the alerting capabilities
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of your monitoring provider. Nomad’s intention is to surface metrics that enable
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users to configure the necessary alerts using their existing monitoring systems
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as a scaffold, rather than to natively support alerting. Here are a few common
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patterns:
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- Export metrics from Nomad to Prometheus using the [StatsD
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exporter][statsd-exporter], define [alerting rules][alerting-rules] in
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Prometheus, and use [Alertmanager][alertmanager] for summarization and
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routing/notifications (to PagerDuty, Slack, etc.). A similar workflow is
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supported for [Datadog][datadog-alerting].
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- Periodically submit test jobs into Nomad to determine if your application
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deployment pipeline is working end-to-end. This pattern is well-suited to
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batch processing workloads.
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- Deploy Nagios on Nomad. Centrally manage Nomad job files and add the Nagios
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monitor when a new Nomad job is added. When a job is removed, remove the
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Nagios monitor. Map Consul alerts to the Nagios monitor. This provides a
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job-specific alerting system.
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- Write a script that looks at the history of each batch job to determine
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whether or not the job is in an unhealthy state, updating your monitoring
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system as appropriate. In many cases, it may be ok if a given batch job fails
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occasionally, as long as it goes back to passing.
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# Key Performance Indicators
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The sections below cover a number of important metrics
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## Consensus Protocol (Raft)
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Nomad uses the Raft consensus protocol for leader election and state
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replication. Spurious leader elections can be caused by networking issues
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between the servers or insufficient CPU resources. Users in cloud environments
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often bump their servers up to the next instance class with improved networking
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and CPU to stabilize leader elections. The `nomad.raft.leader.lastContact` metric
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is a general indicator of Raft latency which can be used to observe how Raft
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timing is performing and guide the decision to upgrade to more powerful servers.
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`nomad.raft.leader.lastContact` should not get too close to the leader lease
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timeout of 500ms.
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## Federated Deployments (Serf)
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Nomad uses the membership and failure detection capabilities of the Serf library
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to maintain a single, global gossip pool for all servers in a federated
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deployment. An uptick in `member.flap` and/or `msg.suspect` is a reliable indicator
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that membership is unstable.
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## Scheduling
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The following metrics allow an operator to observe changes in throughput at the
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various points in the scheduling process (evaluation, scheduling/planning, and
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placement):
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- **nomad.broker.total_blocked** - The number of blocked evaluations.
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- **nomad.worker.invoke_scheduler.\<type\>** - The time to run the scheduler of
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the given type.
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- **nomad.plan.evaluate** - The time to evaluate a scheduler Plan.
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- **nomad.plan.submit** - The time to submit a scheduler Plan.
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- **nomad.plan.queue_depth** - The number of scheduler Plans waiting to be
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evaluated.
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Upticks in any of the above metrics indicate a decrease in scheduler throughput.
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## Capacity
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The importance of monitoring resource availability is workload specific. Batch
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processing workloads often operate under the assumption that the cluster should
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be at or near capacity, with queued jobs running as soon as adequate resources
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become available. Clusters that are primarily responsible for long running
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services with an uptime requirement may want to maintain headroom at 20% or
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more. The following metrics can be used to assess capacity across the cluster on
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a per client basis:
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- **nomad.client.allocated.cpu**
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- **nomad.client.unallocated.cpu**
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- **nomad.client.allocated.disk**
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- **nomad.client.unallocated.disk**
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- **nomad.client.allocated.iops**
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- **nomad.client.unallocated.iops**
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- **nomad.client.allocated.memory**
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- **nomad.client.unallocated.memory**
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## Task Resource Consumption
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The metrics listed [here][allocation-metrics] can be used to track resource
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consumption on a per task basis. For user facing services, it is common to alert
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when the CPU is at or above the reserved resources for the task.
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## Job and Task Status
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We do not currently surface metrics for job and task/allocation status, although
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we will consider adding metrics where it makes sense.
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## Runtime Metrics
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Runtime metrics apply to all clients and servers. The following metrics are
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general indicators of load and memory pressure:
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- **nomad.runtime.num_goroutines**
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- **nomad.runtime.heap_objects**
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- **nomad.runtime.alloc_bytes**
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It is recommended to alert on upticks in any of the above, server memory usage
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in particular.
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[alerting-rules]: https://prometheus.io/docs/prometheus/latest/configuration/alerting_rules/
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[alertmanager]: https://prometheus.io/docs/alerting/alertmanager/
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[allocation-metrics]: /docs/telemetry/metrics#allocation-metrics
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[circonus-telem]: /docs/configuration/telemetry#circonus
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[collection-interval]: /docs/configuration/telemetry#collection_interval
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[datadog-alerting]: https://www.datadoghq.com/blog/monitoring-101-alerting/
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[datadog-telem]: /docs/configuration/telemetry#datadog
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[prometheus-telem]: /docs/configuration/telemetry#prometheus
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[metrics-api-endpoint]:/1/api-docs/metrics
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[metric-types]: /docs/telemetry/metrics#metric-types
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[statsd-exporter]: https://github.com/prometheus/statsd_exporter
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[statsd-telem]: /docs/configuration/telemetry#statsd
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[statsite-telem]: /docs/configuration/telemetry#statsite
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[tagged-metrics]: /docs/telemetry/metrics#tagged-metrics
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[telemetry-stanza]: /docs/configuration/telemetry
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