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 attributes, Sensu agents report the resulting event under the proxy entity instead of the agent entity.

Use a proxy entity to monitor a website

In this section, you’ll monitor the status of sensu.io by configuring a check with a proxy entity name so that Sensu creates an entity that represents the site and reports the status of the site under this entity.

Register dynamic runtime assets

To power the check, you’ll use the Sensu Plugins HTTP dynamic runtime asset. The Sensu Plugins HTTP asset includes check-http.rb, which your check will rely on.

The Sensu assets packaged from Sensu Plugins HTTP are built against the Sensu Ruby runtime environment, so you also need to add the Sensu Ruby Runtime dynamic runtime asset. Sensu Ruby Runtime delivers the Ruby executable and supporting libraries the check will need to run the check-http.rb plugin.

Use sensuctl asset add to register the Sensu Plugins HTTP dynamic runtime asset, sensu-plugins/sensu-plugins-http:

sensuctl asset add sensu-plugins/sensu-plugins-http:6.0.0 -r sensu-plugins-http

The response will indicate that the asset was added:

fetching bonsai asset: sensu-plugins/sensu-plugins-http:6.0.0
added asset: sensu-plugins/sensu-plugins-http:6.0.0

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 ["sensu-plugins-http"].

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

You can also download the dynamic runtime asset definition for Debian or Alpine from Bonsai and register the asset with sensuctl create --file filename.yml or sensuctl create --file filename.json.

Then, use the following sensuctl example to register the Sensu Ruby Runtime dynamic runtime asset, sensu/sensu-ruby-runtime:

sensuctl asset add sensu/sensu-ruby-runtime:0.1.0 -r sensu-ruby-runtime

The response will indicate that the asset was added:

fetching bonsai asset: sensu/sensu-ruby-runtime:0.1.0
added asset: sensu/sensu-ruby-runtime:0.1.0

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 ["sensu-ruby-runtime"].

You can also download the dynamic runtime asset definition from Bonsai and register the asset using sensuctl create --file filename.yml or sensuctl create --file filename.json.

Use sensuctl to confirm that both dynamic runtime assets are ready to use:

sensuctl asset list

The response should list the sensu-plugins-http and sensu-ruby-runtime dynamic runtime assets:

          Name                                                URL                                       Hash    
────────────────────────── ─────────────────────────────────────────────────────────────────────────── ───────── 
 sensu-plugins-http         //assets.bonsai.sensu.io/.../sensu-plugins-http_6.0.0_centos_linux_amd64.tar.gz         31023af  
 sensu-ruby-runtime         //assets.bonsai.sensu.io/.../sensu-ruby-runtime_0.1.0_ruby-2.4.4_centos_linux_amd64.tar.gz     338b88b 

Create the check

Now that the dynamic runtime assets are registered, you can create a check named check-sensu-site to run the command check-http.rb -u https://sensu.io with the sensu-plugins-http and sensu-ruby-runtime dynamic runtime assets, at an interval of 60 seconds, for all agents subscribed to the proxy subscription, using the sensu-site proxy entity name. To avoid duplicate events, add the round_robin attribute to distribute the check execution across all agents subscribed to the proxy subscription.

Create a file named check.yml or check.json in your Sensu installation to store the check definition. Copy this this check definition into the check.yml or check.json file and save it:

---
type: CheckConfig
api_version: core/v2
metadata:
  name: check-sensu-site
  namespace: default
spec:
  command: check-http.rb -u https://sensu.io
  interval: 60
  proxy_entity_name: sensu-site
  publish: true
  round_robin: true
  runtime_assets:
  - sensu-plugins-http
  - sensu-ruby-runtime
  subscriptions:
  - proxy

{
  "type": "CheckConfig",
  "api_version": "core/v2",
  "metadata": {
    "name": "check-sensu-site",
    "namespace": "default"
  },
  "spec": {
    "command": "check-http.rb -u https://sensu.io",
    "runtime_assets": [
      "sensu-plugins-http",
      "sensu-ruby-runtime"
    ],
    "interval": 60,
    "proxy_entity_name": "sensu-site",
    "publish": true,
    "round_robin": true,
    "subscriptions": [
      "proxy"
    ]
  }
}

Use sensuctl to add check-sensu-site to Sensu directly from the check.yml or check.json file:

sensuctl create --file check.yml

sensuctl create --file check.json

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?  
────────────────── ────────────────────────────────── ────────── ────── ───────── ───── ─────────────── ────────── ─────────────────────────────────────── ─────── ────────── ────────
 check-sensu-site   check-http.rb -u https://sensu.io         60                0     0   proxy                      sensu-plugins-http,sensu-ruby-runtime             true     false

Add the subscription

To run the check, you’ll need a Sensu agent with the subscription proxy. After you install an agent, use sensuctl to add the proxy subscription to the entity the Sensu agent is observing.

In the following command, Replace <entity_name> with the name of the entity on your system. Then, run:

sensuctl entity update <entity_name>

• For Entity Class, press enter.
• For Subscriptions, type proxy and press enter.

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   2019-01-16 21:50:03 +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:    CheckHttp OK: 200, 72024 bytes
Status:    0
History:   0,0,0
Silenced:  false
Timestamp: 2021-04-16 22:02:02 +0000 UTC
UUID:      d34599cb-5596-9ad4-51ad-cc3d942690c6

You can also see 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 the proxy_requests check attribute along with entity labels and token substitution to monitor three sites with the same check. Before you start, register the sensu-plugins-http and sensu-ruby-runtime dynamic runtime assets if you haven’t already.

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.

Create a file named entities.yml or entities.json in your Sensu installation and add the following entity definitions:

---
type: Entity
api_version: core/v2
metadata:
  name: sensu-docs
  namespace: default
  labels:
    proxy_type: website
    url: https://docs.sensu.io
spec:
  entity_class: proxy

{
  "type": "Entity",
  "api_version": "core/v2",
  "metadata": {
    "name": "sensu-docs",
    "namespace": "default",
    "labels": {
      "proxy_type": "website",
      "url": "https://docs.sensu.io"
    }
  },
  "spec": {
    "entity_class": "proxy"
  }
}

---
type: Entity
api_version: core/v2
metadata:
  name: packagecloud-site
  namespace: default
  labels:
    proxy_type: website
    url: https://packagecloud.io
spec:
  entity_class: proxy

{
  "type": "Entity",
  "api_version": "core/v2",
  "metadata": {
    "name": "packagecloud-site",
    "namespace": "default",
    "labels": {
      "proxy_type": "website",
      "url": "https://packagecloud.io"
    }
  },
  "spec": {
    "entity_class": "proxy"
  }
}

---
type: Entity
api_version: core/v2
metadata:
  name: github-site
  namespace: default
  labels:
    proxy_type: website
    url: https://github.com
spec:
  entity_class: proxy

{
  "type": "Entity",
  "api_version": "core/v2",
  "metadata": {
    "name": "github-site",
    "namespace": "default",
    "labels": {
      "proxy_type": "website",
      "url": "https://github.com"
    }
  },
  "spec": {
    "entity_class": "proxy"
  }
}

Now you can use sensuctl to add these proxy entities to Sensu directly from the entities.yml or entities.json file:

sensuctl create --file entities.yml

sensuctl create --file entities.json

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   2019-01-16 23:05:03 +0000 UTC  
 sensu-docs          proxy                                       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.

Create a file called check-http.yml or check-http.json in your Sensu installation and add the following check definition:

---
type: CheckConfig
api_version: core/v2
metadata:
  name: check-http
  namespace: default
spec:
  command: check-http.rb -u {{ .labels.url }}
  interval: 60
  proxy_requests:
    entity_attributes:
    - entity.entity_class == 'proxy'
    - entity.labels.proxy_type == 'website'
  publish: true
  runtime_assets:
  - sensu-plugins-http
  - sensu-ruby-runtime
  subscriptions:
  - proxy

{
  "type": "CheckConfig",
  "api_version": "core/v2",
  "metadata": {
    "name": "check-http",
    "namespace": "default"
  },
  "spec": {
    "command": "check-http.rb -u {{ .labels.url }}",
    "runtime_assets": [
      "sensu-plugins-http",
      "sensu-ruby-runtime"
    ],
    "interval": 60,
    "subscriptions": [
      "proxy"
    ],
    "publish": true,
    "proxy_requests": {
      "entity_attributes": [
        "entity.entity_class == 'proxy'",
        "entity.labels.proxy_type == 'website'"
      ]
    }
  }
}

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, you can use token substitution to apply the correct url in the check command.

Use sensuctl to add the check-http check to Sensu directly from the check-http.yml or check-http.json file:

sensuctl create --file check-http.yml

sensuctl create --file check-http.json

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?
───────────────── ─────────────────────────────────── ────────── ────── ───────── ───── ─────────────── ────────── ─────────────────────────────────────── ─────── ────────── ────────
  check-http        check-http.rb -u {{ .labels.url }}         60                0     0   proxy                     sensu-plugins-http,sensu-ruby-runtime           true       false                                     

Validate the check

Before you validate the check, make sure that you’ve registered the sensu-plugins-http and sensu-ruby-runtime dynamic runtime assets and added the proxy subscription to a Sensu agent.

Use sensuctl to confirm that Sensu is monitoring docs.sensu.io, packagecloud.io, and github.com with the check-http, 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            
─────────────────── ───────────────────── ──────── ──────── ────────── ─────────────────────────────── 
github-site         check-http                           0   false      2019-01-17 17:10:31 +0000 UTC  
packagecloud-site   check-http                           0   false      2019-01-17 17:10:34 +0000 UTC  
sensu-centos        keepalive               ...          0   false      2019-01-17 17:10:34 +0000 UTC  
sensu-docs          check-http                           0   false      2019-01-17 17:06:59 +0000 UTC  

Next steps

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.

Now that you know how to run a proxy check to verify the status of a website and use proxy requests to run a check on two different proxy entities based on label evaluation, read these recommended resources:

• Proxy checks
• Assets reference
• Send Slack alerts with handlers