open-consul/website/source/docs/guides/sentinel.html.markdown.erb

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---
layout: "docs"
page_title: "Sentinel in Consul"
sidebar_current: "docs-guides-sentinel"
description: |-
Consul Enterprise uses Sentinel to augment the built-in ACL system to provide advanced policy enforcement. Sentinel policies can currently execute on KV modify and service registration.
---
# Sentinel Overview
[//]: # ( ~> The Sentinel functionality described here is available only in )
[//]: # ( [Consul Enterprise](https://www.hashicorp.com/products/consul/) version 1.0.0 and later. )
<%= enterprise_alert :consul %>
Consul 1.0 adds integration with [Sentinel](https://hashicorp.com/sentinel) for policy enforcement.
Sentinel policies help extend the ACL system in Consul beyond the static "read", "write", and "deny"
policies to support full conditional logic, and integration with external systems.
## Sentinel in Consul
Sentinel policies are applied during writes to the KV Store.
ACL policy definitions take a `sentinel` field specifying the code and the enforcement level.
Here's an example:
```text
sentinel {
code = "import \"strings\"
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main = rule { strings.has_suffix(value,\"foo\") }"
enforcementlevel = "soft-mandatory"
}
```
This policy ensures that the value written during a KV update must end with "foo".
If the `enforcementlevel` property is not set, it defaults to "hard-mandatory".
## Imports
Consul imports all the [standard imports](https://docs.hashicorp.com/sentinel/imports/)
from Sentinel. All functions in these imports are available to be used in policies.
## Injected Variables
Consul passes some context as variables into Sentinel, which are available to use inside any policies you write.
#### Variables injected during KV store writes
| Variable Name | Type | Description |
| ------------- | -------- | ----------- |
| `key` | `string` | Key being written |
| `value` | `string` | Value being written |
| `flags` | `uint64` | [Flags](/api/kv.html#flags) |
## Examples
The following are some examples of ACL policies with Sentinel rules.
### Any values stored under the key prefix "foo" must end with "bar"
```text
key "foo" {
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policy = "write"
sentinel {
code = "import \"strings\"
main = rule { strings.has_suffix(value, \"bar\") }"
}
}
```
### The key "foo" can only be updated during business hours.
```text
key "foo" {
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policy = "write"
sentinel {
code = "import \"time\"
main = rule { time.hour > 8 and time.hour < 17 }"
}
}
```