Monitor external resources with proxy entities

Proxy entities allow Sensu to monitor external resources on systems and devices where a Sensu agent cannot be installed, like a network switch or a website. You can create proxy entities with sensuctl, the Sensu API, and the proxy_entity_name check attribute. When executing checks that include a proxy_entity_name or proxy_requests attribute, Sensu agents report the resulting event under the proxy entity instead of the agent entity.

This guide explains how to use a proxy entity to monitor website status, as well as how to use the proxy checks to monitor a group of websites.

Requirements

To follow this guide, install the Sensu backend, make sure at least one Sensu agent is running, and configure sensuctl to connect to the backend as the admin user.

Use a proxy entity to monitor a website

In this section, you’ll use sensuctl to configure a check with a proxy entity name to monitor the status of https://sensu.io/ so that Sensu creates an entity that represents the site and reports the status of the site under this entity.

Configure a Sensu entity

To run the check, you’ll need a Sensu agent entity with the subscription run_proxies. Use sensuctl to add the run_proxies subscription to the entity the Sensu agent is observing.

NOTE: To find your entity name, run sensuctl entity list. The ID is the name of your entity.

Before you run the following code, replace <ENTITY_NAME> with the name of the entity on your system.

sensuctl entity update <ENTITY_NAME>

For Entity Class, press enter.
For Subscriptions, type run_proxies and press enter.

Before you continue, confirm both Sensu services are running:

systemctl status sensu-backend && systemctl status sensu-agent

The response should indicate active (running) for both the Sensu backend and agent.

Register dynamic runtime asset

To power the check for https://sensu.io/ status, you’ll use the sensu/http-checks dynamic runtime asset. This community-tier asset includes the http status command that your check will rely on.

Use sensuctl asset add to register the dynamic runtime asset:

sensuctl asset add sensu/http-checks:0.5.0 -r http-checks

The response will indicate that the asset was added:

fetching bonsai asset: sensu/http-checks:0.5.0
added asset: sensu/http-checks:0.5.0

You have successfully added the Sensu asset resource, but the asset will not get downloaded until
it's invoked by another Sensu resource (ex. check). To add this runtime asset to the appropriate
resource, populate the "runtime_assets" field with ["http-checks"].

This example uses the -r (rename) flag to specify a shorter name for the dynamic runtime asset: http-checks.

Use sensuctl to confirm that the dynamic runtime asset is ready to use:

sensuctl asset list

The response should list the sensu/http-checks dynamic runtime asset (renamed to http-checks):

     Name                                       URL                                    Hash    
────────────── ───────────────────────────────────────────────────────────────────── ──────────
  http-checks   //assets.bonsai.sensu.io/.../http-checks_0.5.0_windows_amd64.tar.gz   52ae075  
  http-checks   //assets.bonsai.sensu.io/.../http-checks_0.5.0_darwin_amd64.tar.gz    72d0f15  
  http-checks   //assets.bonsai.sensu.io/.../http-checks_0.5.0_linux_armv7.tar.gz     ef18587  
  http-checks   //assets.bonsai.sensu.io/.../http-checks_0.5.0_linux_arm64.tar.gz     3504ddf  
  http-checks   //assets.bonsai.sensu.io/.../http-checks_0.5.0_linux_386.tar.gz       60b8883  
  http-checks   //assets.bonsai.sensu.io/.../http-checks_0.5.0_linux_amd64.tar.gz     1db73a8

NOTE: Sensu does not download and install dynamic runtime asset builds onto the system until they are needed for command execution.

Create the check

Now that the dynamic runtime asset is registered, you can create a check named check-sensu-site to run the command http-check --url https://sensu.io with the sensu/http-checks dynamic runtime asset, at an interval of 15 seconds, for all agents subscribed to the run_proxies subscription, using the sensu-site proxy entity name.

The check includes the round_robin attribute set to true to distribute the check execution across all agents subscribed to the run_proxies subscription and avoid duplicate events.

To create the check-sensu-site check, run:

cat << EOF | sensuctl create
---
type: CheckConfig
api_version: core/v2
metadata:
  name: check-sensu-site
spec:
  command: http-check --url https://sensu.io
  interval: 15
  proxy_entity_name: sensu-site
  publish: true
  round_robin: true
  runtime_assets:
  - http-checks
  subscriptions:
  - run_proxies
EOF

cat << EOF | sensuctl create
{
  "type": "CheckConfig",
  "api_version": "core/v2",
  "metadata": {
    "name": "check-sensu-site"
  },
  "spec": {
    "command": "http-check --url https://sensu.io",
    "interval": 15,
    "proxy_entity_name": "sensu-site",
    "publish": true,
    "round_robin": true,
    "runtime_assets": [
      "http-checks"
    ],
    "subscriptions": [
      "run_proxies"
    ]
  }
}
EOF

Use sensuctl to confirm that Sensu added the check:

sensuctl check list

The response should list check-sensu-site:

        Name                      Command                Interval   Cron   Timeout   TTL   Subscriptions   Handlers     Assets      Hooks   Publish?   Stdin?   Metric Format   Metric Handlers  
─────────────────── ─────────────────────────────────── ────────── ────── ───────── ───── ─────────────── ────────── ───────────── ─────── ────────── ──────── ─────────────── ──────────────────
  check-sensu-site   http-check --url https://sensu.io         15                0     0   proxy                      http-checks           true       false

Validate the check

Use sensuctl to confirm that Sensu created sensu-site. It might take a few moments for Sensu to execute the check and create the proxy entity.

sensuctl entity list

The response should list the sensu-site proxy entity:

       ID        Class    OS           Subscriptions                   Last Seen            
─────────────── ─────── ─────── ─────────────────────────── ────────────────────────────────
  sensu-centos   agent   linux   proxy,entity:sensu-centos   2021-10-21 19:20:04 +0000 UTC  
  sensu-site     proxy           entity:sensu-site           N/A

Then, use sensuctl to confirm that Sensu is monitoring sensu-site with the check-sensu-site check:

sensuctl event info sensu-site check-sensu-site

The response should list check-sensu-site status and history data for the sensu-site proxy entity:

=== sensu-site - check-sensu-site
Entity:    sensu-site
Check:     check-sensu-site
Output:    http-check OK: HTTP Status 200 for https://sensu.io
Status:    0
History:   0
Silenced:  false
Timestamp: 2021-10-21 19:20:06 +0000 UTC
UUID:      xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can also view the new proxy entity in your Sensu web UI.

Use proxy requests to monitor a group of websites

Suppose that instead of monitoring just sensu.io, you want to monitor multiple sites, like docs.sensu.io, packagecloud.io, and github.com. In this section, you’ll use sensuctl to configure the proxy_requests check attribute, entity labels, and token substitution required to monitor three sites with the same check.

Before you start, use sensuctl asset add to register the sensu/http-checks dynamic runtime asset if you haven’t already:

sensuctl asset add sensu/http-checks:0.5.0 -r http-checks

Also, add the run_proxies subscription to a Sensu agent entity. Replace <ENTITY_NAME> with the name of the entity on your system:

sensuctl entity update <ENTITY_NAME>

For Entity Class, press enter.
For Subscriptions, type run_proxies and press enter.

Create proxy entities

Instead of creating a proxy entity using the proxy_entity_name check attribute, use sensuctl to create proxy entities to represent the three sites you want to monitor. Your proxy entities need the entity_class attribute set to proxy to mark them as proxy entities as well as a few custom labels to identify them as a group and pass in individual URLs.

To add the proxy entity definitions, run:

cat << EOF | sensuctl create
---
type: Entity
api_version: core/v2
metadata:
  name: sensu-docs
  labels:
    proxy_type: website
    url: https://docs.sensu.io
spec:
  entity_class: proxy
---
type: Entity
api_version: core/v2
metadata:
  name: packagecloud-site
  labels:
    proxy_type: website
    url: https://packagecloud.io
spec:
  entity_class: proxy
---
type: Entity
api_version: core/v2
metadata:
  name: github-site
  labels:
    proxy_type: website
    url: https://github.com
spec:
  entity_class: proxy
EOF

cat << EOF | sensuctl create
{
  "type": "Entity",
  "api_version": "core/v2",
  "metadata": {
    "name": "sensu-docs",
    "labels": {
      "proxy_type": "website",
      "url": "https://docs.sensu.io"
    }
  },
  "spec": {
    "entity_class": "proxy"
  }
}
{
  "type": "Entity",
  "api_version": "core/v2",
  "metadata": {
    "name": "packagecloud-site",
    "labels": {
      "proxy_type": "website",
      "url": "https://packagecloud.io"
    }
  },
  "spec": {
    "entity_class": "proxy"
  }
}
{
  "type": "Entity",
  "api_version": "core/v2",
  "metadata": {
    "name": "github-site",
    "labels": {
      "proxy_type": "website",
      "url": "https://github.com"
    }
  },
  "spec": {
    "entity_class": "proxy"
  }
}
EOF

PRO TIP: When you create proxy entities, you can add any custom labels that make sense for your environment. For example, when monitoring a group of routers, you may want to add ip_address labels.

Use sensuctl to confirm that the entities were added:

sensuctl entity list

The response should list the new sensu-docs, packagecloud-site, and github-site proxy entities:

         ID           Class    OS           Subscriptions                   Last Seen            
──────────────────── ─────── ─────── ─────────────────────────── ────────────────────────────────
  github-site         proxy                                       N/A                            
  packagecloud-site   proxy                                       N/A                            
  sensu-centos        agent   linux   proxy,entity:sensu-centos   2021-10-21 19:23:04 +0000 UTC  
  sensu-docs          proxy                                       N/A                            
  sensu-site          proxy           entity:sensu-site           N/A

Create a reusable HTTP check

Now that you have three proxy entities set up, each with a proxy_type and url label, you can use proxy requests and token substitution to create a single check that monitors all three sites.

The check includes the round_robin attribute set to true to distribute the check execution across all agents subscribed to the run_proxies subscription and avoid duplicate events.

To create the following check definition, run:

cat << EOF | sensuctl create
---
type: CheckConfig
api_version: core/v2
metadata:
  name: check-http
spec:
  command: 'http-check --url {{ .labels.url }}'
  interval: 15
  proxy_requests:
    entity_attributes:
      - entity.entity_class == 'proxy'
      - entity.labels.proxy_type == 'website'
  publish: true
  round_robin: true
  runtime_assets:
    - http-checks
  subscriptions:
    - run_proxies
EOF

cat << EOF | sensuctl create
{
  "type": "CheckConfig",
  "api_version": "core/v2",
  "metadata": {
    "name": "check-http"
  },
  "spec": {
    "command": "http-check --url {{ .labels.url }}",
    "interval": 15,
    "proxy_requests": {
      "entity_attributes": [
        "entity.entity_class == 'proxy'",
        "entity.labels.proxy_type == 'website'"
      ]
    },
    "publish": true,
    "runtime_assets": [
      "http-checks"
    ],
    "round_robin": true,
    "subscriptions": [
      "run_proxies"
    ]
  }
}
EOF

Your check-http check uses the proxy_requests attribute to specify the applicable entities. In this case, you want to run the check-http check on all entities of entity class proxy and proxy type website. Because you’re using this check to monitor multiple sites, the check command uses token substitution to apply the correct url.

Use sensuctl to confirm that Sensu created the check:

sensuctl check list

The response should include the check-http check:

        Name                      Command                 Interval   Cron   Timeout   TTL   Subscriptions   Handlers     Assets      Hooks   Publish?   Stdin?   Metric Format   Metric Handlers  
─────────────────── ──────────────────────────────────── ────────── ────── ───────── ───── ─────────────── ────────── ───────────── ─────── ────────── ──────── ─────────────── ──────────────────
  check-http         http-check --url {{ .labels.url }}         15                0     0   proxy                      http-checks           true       false                                     
  check-sensu-site   http-check --url https://sensu.io          15                0     0   proxy                      http-checks           true       false

Validate the check

Use sensuctl to confirm that Sensu is monitoring docs.sensu.io, packagecloud.io, and github.com with the check-http check, returning a status of 0 (OK):

sensuctl event list

The response should list check status data for the sensu-docs, packagecloud-site, and github-site proxy entities:

       Entity              Check                                         Output                                   Status   Silenced             Timestamp                             UUID                  
──────────────────── ────────────────── ──────────────────────────────────────────────────────────────────────── ──────── ────────── ─────────────────────────────── ───────────────────────────────────────
  github-site         check-http         http-check OK: HTTP Status 200 for https://github.com                         0   false      2021-10-21 19:27:04 +0000 UTC   xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx  
                                                                                                                                                                                                            
  packagecloud-site   check-http         http-check OK: HTTP Status 200 for https://packagecloud.io                    0   false      2021-10-21 19:27:04 +0000 UTC   xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx  
                                                                                                                                                                                                            
  sensu-centos        keepalive          Keepalive last sent from sensu-centos at 2021-10-21 19:27:44 +0000 UTC        0   false      2021-10-21 19:27:44 +0000 UTC   xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx  
  sensu-docs          check-http         http-check OK: HTTP Status 200 for https://docs.sensu.io                      0   false      2021-10-21 19:27:03 +0000 UTC   xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx  
                                                                                                                                                                                                            
  sensu-site          check-sensu-site   http-check OK: HTTP Status 200 for https://sensu.io                           0   false      2021-10-21 19:27:05 +0000 UTC   xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

What’s next

Now that you know how to run proxy checks to verify website status, you can receive alerts based on the events your checks create. Configure three more Sensu resources to start receiving alerts:

Event filters, which the Sensu backend will apply to the observation data in events. Sensu then sends any events the filters do not remove for processing.
Handlers, which process the events that filters do not remove.
Pipelines, which are Sensu resources composed of observation event processing workflows made up of filters, mutators, and handlers. When you list a pipeline in a check definition, all the observability events that the check produces will be processed according to the pipeline’s workflows.

Follow any of these guides to learn how to configure event filters, handlers, and pipelines and start sending alerts based on event data:

You can also send metrics and status data to Sumo Logic.

Read more about the Sensu features you used in this guide:

The files you created with check and entity definitions can become part of your monitoring as code repository. Storing your Sensu configurations the same way you would store code means they are portable and repeatable. Monitoring as code makes it possible to move to a more robust deployment without losing what you’ve started here and reproduce one environment’s configuration in another.

Monitor external resources with proxy entities

Requirements

Use a proxy entity to monitor a website

Configure a Sensu entity

Register dynamic runtime asset

Create the check

Validate the check

Use proxy requests to monitor a group of websites

Create proxy entities

Create a reusable HTTP check

Validate the check

What’s next

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