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In-depth topics

Table of contents

  1. Metric collection
    1. Description
    2. Usage
      1. StdoutCollector (default)
      2. PrometheusCollector
      3. DatadogCollector
    3. Use Case: Prometheus + Grafana + AlertManager
    4. Use Case: Datadog
  2. Inventory file
  3. Extend Powerfulseal
    1. Custom Metric Collectors
    2. Custom Cloud Drivers
    3. Custom Filters

Metric collection


The purpose of metric collection is to keep track of events which you may consider useful to be monitored (e.g., via Grafana). Three metric collectors have been implemented:

  • StdoutCollector, a “no-op” collector which simply prints that an event has occurred to stdout
  • PrometheusCollector, which sends metrics to the default Prometheus registry and exposes them via Prometheus internal web server
  • DatadogCollector, which sends metrics to the DogStatsD aggregation service bundled with the Datadog Agent.

Like cloud drivers, metric collectors are extensible by subscribing to the AbstractCollector interface. Likewise, AbstractCollector makes it easy to add your own metrics.

The metric collectors collect the following events:

Metric Labels (Metadata) Description Justification
seal_pod_kills_total status, namespace, name Number of pods killed (including failures) Example alerts include number of pod kills failing in the past five minutes or the ratio between successful and failed pod kills in a time range. If a pod cannot be killed, it could be an an unresponsive state or there may be a problem with keeping Kubernetes synchronised to the node.
seal_nodes_stopped_total status, uid, name Number of nodes killed (including failures) Example alerts include number of node stops failing in the past five minutes or the ratio between successful and failed node stops. If a node cannot be stopped, it could be in an unresponsive state.
seal_execute_failed_total uid, name Tracks failure of command executions Commands executions failing is a general case of errors which should be brought to the user’s attention.
seal_empty_filter_total N/A Cases where filtering returns an empty result If the user’s policy is designed to model common levels of failures, then having no nodes/pods after filtering could mean that insufficient resources have been provisioned for the system to withstand failure.
seal_probability_filter_not_passed_total N/A Cases where the probability filter decides to skip all nodes Useful to track long-term in order to ensure that probability distribution is as expected.
seal_empty_match_total source (either nodes or pods) Cases where matching returns an empty result See seal_empty_filter_total
add_scenario_counter_metric name of the scenario, success or fail Counts scenarios and their results Can be used to alert on when a scenario starts failing


StdoutCollector (default)

To print metrics to stdout, use the --stdout-collector flag.


To collect metrics, run PowerfulSeal with the --prometheus-collector flag, along with the --prometheus-host and --prometheus-port flags. Metrics will be exposed under a web server with URL http://HOST:PORT/metrics.


This collector relies on DogStatsD server (bundled with the Datadog Agent), so a working instance is expected.

To collect metrics, run PowerfulSeal with the --datadog-collector flag.

Use Case: Prometheus + Grafana + AlertManager

Grafana example example

A common use case is to use a combination of Prometheus, Grafana and AlertManager in order to increase visibility of potential issues.

In order to configure this integration, follow the steps below. (The below instructions assume that Prometheus and Grafana are already set up.)

  1. Open your Prometheus configuration file (e.g., /etc/prometheus/prometheus.yml) and add a scrape_configs job with the host IP and a chosen port for the server PowerfulSeal will be run on: ```yaml scrape_configs:
    • job_name: powerfulseal scrape_interval: 5s scrape_timeout: 5s metrics_path: /metrics scheme: http static_configs:
      • targets:
        • labels: name: powerfulseal ```

  2. Add an alert file (e.g., seal.alerts.yml) to your Prometheus configuration path with your alerting rules (example here)
  3. Update alertmanager.yml to handle the alerting rules, for example:
       resolve_timeout: 5m
       receiver: 'default'
       - receiver: 'seal'
           type: seal
     # A list of notification receivers.
       - name: default
       - name: seal
  4. Start PowerfulSeal with the --prometheus-collector, --prometheus-host and --prometheus-port flags, and restart Prometheus. Metrics should begin to appear.
  5. Ensure Grafana has your Prometheus server added as a data source and create a new Grafana dashboard with the metrics (example here - note that the data source name may need to be changed)

Use Case: Datadog

Datadog example example

It’s common to use Datadog in order to increase visibility of potential issues.

In order to configure this properly, follow the steps below. (The below instructions assume that Datadog Agent is already set up.)

  1. Start PowerfulSeal with the --datadog-collector flag. Metrics should begin to appear on Datadog.

  2. Create a new dashboard with the collected metrics (example here).

  3. Configure alerting with Monitors, to give you the ability to know when critical changes are occurring.

Inventory file

PowerfulSeal can use an ansible-style inventory file (in ini format)




Extend Powerfulseal

Custom Metric Collectors

Custom Cloud Drivers

Custom Filters

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