Hooks reference
Hooks are reusable commands the agent executes in response to a check result before creating an observability event.
You can create, manage, and reuse hooks independently of checks.
Hooks enrich observability event context by gathering relevant information based on the exit status code of a check (ex: 1
).
Hook commands can also receive JSON serialized Sensu client data via stdin.
Hook example
You can use hooks to automate data gathering for incident triage. This example demonstrates a check hook to capture the process tree when a process is not running:
---
type: HookConfig
api_version: core/v2
metadata:
name: process_tree
spec:
command: ps aux
stdin: false
timeout: 60
runtime_assets: null
{
"type": "HookConfig",
"api_version": "core/v2",
"metadata": {
"name": "process_tree"
},
"spec": {
"command": "ps aux",
"timeout": 60,
"stdin": false,
"runtime_assets": null
}
}
Check response types
Each type of response (ex: non-zero
) can contain one or more hooks and correspond to one or more exit status codes.
Hooks are executed in order of precedence, based on their type:
1
to255
ok
warning
critical
unknown
non-zero
You can assign one or more hooks to a check in the check definition.
review the check specification to configure the check_hooks
attribute.
Check hooks
Sensu captures the hook command output, status, executed timestamp, and duration and publishes them in the resulting event.
You can use sensuctl
to view hook command data:
sensuctl event info <entity_name> <check_name> --format yaml
sensuctl event info <entity_name> <check_name> --format wrapped-json
The response lists the specified event, which includes the hook command data:
---
type: Event
api_version: core/v2
metadata:
namespace: default
spec:
check:
...
hooks:
- command: df -hT / | grep '/'
duration: 0.002904412
executed: 1559948435
issued: 0
metadata:
name: root_disk
namespace: default
output: "/dev/mapper/centos-root xfs 41G 1.6G 40G 4% /\n"
status: 0
stdin: false
timeout: 60
{
"type": "Event",
"api_version": "core/v2",
"metadata": {
"namespace": "default"
},
"spec": {
"check": {
"...": "...",
"hooks": [
{
"command": "df -hT / | grep '/'",
"duration": 0.002904412,
"executed": 1559948435,
"issued": 0,
"metadata": {
"name": "root_disk",
"namespace": "default"
},
"output": "/dev/mapper/centos-root xfs 41G 1.6G 40G 4% /\n",
"status": 0,
"stdin": false,
"timeout": 60
}
]
}
}
}
PRO TIP: You can also view complete resource definitions in the Sensu web UI.
Hook specification
Top-level attributes
api_version | |
---|---|
description | Top-level attribute that specifies the Sensu API group and version. For hooks in this version of Sensu, the api_version should always be core/v2 . |
required | Required for hook definitions in wrapped-json or yaml format for use with sensuctl create . |
type | String |
example |
|
metadata | |
---|---|
description | Top-level collection of metadata about the hook that includes name , namespace , and created_by as well as custom labels and annotations . The metadata map is always at the top level of the hook definition. This means that in wrapped-json and yaml formats, the metadata scope occurs outside the spec scope. Read metadata attributes for details. |
required | Required for hook definitions in wrapped-json or yaml format for use with sensuctl create . |
type | Map of key-value pairs |
example |
|
spec | |
---|---|
description | Top-level map that includes the hook spec attributes. |
required | Required for hook definitions in wrapped-json or yaml format for use with sensuctl create . |
type | Map of key-value pairs |
example |
|
type | |
---|---|
description | Top-level attribute that specifies the sensuctl create resource type. Hooks should always be type HookConfig . |
required | Required for hook definitions in wrapped-json or yaml format for use with sensuctl create . |
type | String |
example |
|
Metadata attributes
annotations | |
---|---|
description | Non-identifying metadata to include with observation event data that you can access with event filters. You can use annotations to add data that’s meaningful to people or external tools that interact with Sensu. In contrast to labels, you cannot use annotations in API response filtering, sensuctl response filtering, or web UI views. |
required | false |
type | Map of key-value pairs. Keys and values can be any valid UTF-8 string. |
default | null |
example |
|
created_by | |
---|---|
description | Username of the Sensu user who created the hook or last updated the hook. Sensu automatically populates the created_by field when the hook is created or updated. |
required | false |
type | String |
example |
|
labels | |
---|---|
description | Custom attributes to include with observation event data that you can use for response and web UI view filtering. If you include labels in your event data, you can filter API responses, sensuctl responses, and web UI views based on them. In other words, labels allow you to create meaningful groupings for your data. Limit labels to metadata you need to use for response filtering. For complex, non-identifying metadata that you will not need to use in response filtering, use annotations rather than labels. |
required | false |
type | Map of key-value pairs. Keys can contain only letters, numbers, and underscores and must start with a letter. Values can be any valid UTF-8 string. |
default | null |
example |
|
name | |
---|---|
description | Unique string used to identify the hook. Hook names cannot contain special characters or spaces (validated with Go regex \A[\w\.\-]+\z ). Each hook must have a unique name within its namespace. |
required | true |
type | String |
example |
|
namespace | |
---|---|
description | The Sensu RBAC namespace that this hook belongs to. |
required | false |
type | String |
default | default |
example |
|
Spec attributes
command | |
---|---|
description | Hook command to be executed. |
required | true |
type | String |
example |
|
runtime_assets | |
---|---|
description | Array of Sensu dynamic runtime assets (by their names) required at runtime for execution of the command . |
required | false |
type | Array |
example |
|
stdin | |
---|---|
description | If true , the Sensu agent writes JSON serialized Sensu entity and check data to the command process stdin. Otherwise, false . The command must expect the JSON data via stdin, read it, and close stdin. This attribute cannot be used with existing Sensu check plugins or Nagios plugins because the Sensu agent will wait indefinitely for the hook process to read and close stdin. |
required | false |
type | Boolean |
default | false |
example |
|
timeout | |
---|---|
description | Hook execution duration timeout (hard stop). In seconds. |
required | false |
type | Integer |
default | 60 |
example |
|
Hook for rudimentary auto-remediation
You can use hooks for rudimentary auto-remediation tasks, such as starting a process that is no longer running.
NOTE: Use caution with this approach. Hooks used for auto-remediation will run without regard to the number of event occurrences.
---
type: HookConfig
api_version: core/v2
metadata:
name: restart_nginx
spec:
command: sudo systemctl start nginx
stdin: false
timeout: 60
{
"type": "HookConfig",
"api_version": "core/v2",
"metadata": {
"name": "restart_nginx"
},
"spec": {
"command": "sudo systemctl start nginx",
"timeout": 60,
"stdin": false
}
}
Hook that uses token substitution
You can create check hooks that use token substitution so you can fine-tune check attributes on a per-entity level and re-use the check definition.
NOTE: Token substitution uses entity-scoped metadata, so make sure to set labels at the entity level.
---
type: HookConfig
api_version: core/v2
metadata:
labels:
foo: bar
name: tokensub
spec:
command: tokensub {{ .labels.foo }}
stdin: false
timeout: 60
{
"type": "HookConfig",
"api_version": "core/v2",
"metadata": {
"labels": {
"foo": "bar"
},
"name": "tokensub"
},
"spec": {
"command": "tokensub {{ .labels.foo }}",
"stdin": false,
"timeout": 60
}
}