--- layout: docs page_title: Sentinel policy reference description: >- Use the Nomad Enterprise Sentinel policy feature to implement fine-grained control over jobs, such as restricting when jobs can run or ensuring jobs use specific images. Learn about policy structure, job objects, Access Control List (ACL) token objects, and namespace objects. --- # Sentinel Policy Reference This page provides reference information on using the Nomad Sentinel policy feature to implement fine-grained policies such as restricting when jobs can run or ensuring job use specific images. Learn about policy structure, job objects, Access Control List (ACL) token objects, and namespace objects. ## Introduction to Sentinel Policies In Nomad Enterprise, operators can create Sentinel policies for fine-grained policy enforcement. Sentinel policies build on top of the ACL system and allow operators to define policies such as disallowing jobs to be submitted to production on Fridays or only allowing users to run jobs that use pre-authorized Docker images. Sentinel policies are defined as code, giving operators considerable flexibility to meet compliance requirements. Refer to the [Nomad Sentinel Tutorial][] for more information about deploying Sentinel policies, as well as the documentation for the [`nomad sentinel`][] subcommands. ## Sentinel Policy Structure Sentinel policies are specified in the [Sentinel Language][sentinel]. The language is designed to be understandable for people who are reading and writing policies, while remaining fast to evaluate. There is no limitation on how complex policies can be, but they are in the execution path so care should be taken to avoid adversely impacting performance. In each scope, there are different objects made available for introspection, such a job being submitted. Policies can inspect these objects to apply fine-grained policies. Nomad supports a `submit-job` scope for registering jobs, and a `submit-host-volume` scope for creating or updating dynamic host volumes. ### submit-job scope The following top-level objects are available to policies in the `submit-job` scope automatically, without an explicit import. * `job`: the submitted job. This is a [Sentinel Job Object](#sentinel-job-objects). * `existing_job`: the previous version of the job. If `job_exists` is true, this is always non-nil. This is also a [Sentinel Job Object](#sentinel-job-objects). * `job_exists`: a boolean field that indicates that a previous version of the job exists. * `nomad_acl_token`: the ACL token the job was submitted with. This is a [Sentinel Nomad ACL Token Object](#sentinel-acl-token-objects). * `namespace`: the namespace the job is in. This is a [Sentinel Nomad Namespace Object](#sentinel-namespace-objects). ### submit-host-volume scope The following top-level objects are available to policies in the `submit-host-volume` scope automatically, without an explicit import. * `volume`: the submitted volume. This is a [Sentinel Dynamic Host Volume Object](#sentinel-dynamic-host-volume-objects). * `existing_volume`: the previous version of the volume. If `volume_exists` is true, this is always non-nil. This is also a [Sentinel Dynamic Host Volume Object](#sentinel-dynamic-host-volume-objects). `volume_exists`: a boolean field that indicates that a previous version of the volume exists. * `nomad_acl_token`: the ACL token the job was submitted with. This is a [Sentinel Nomad ACL Token Object](#sentinel-acl-token-objects). * `namespace`: the namespace the job is in. This is a [Sentinel Nomad Namespace Object](#sentinel-namespace-objects). * `node`: the node the volume has been placed on. This is a [Sentinel Node Object](#sentinel-node-objects). * `node_pool`: the node pool of the node the volume has been placed on. This is a [Sentinel Node Pool Object](#sentinel-node-pool-objects). ### submit-csi-volume scope The following top-level objects are available to policies in the `submit-csi-volume` scope automatically, without an explicit import. - `volume`: the submitted volume. This is a [Sentinel CSI Volume Object](#sentinel-csi-volume-objects). - `existing_volume`: the previous version of the volume. If `volume_exists` is true, this is always non-nil. This is also a [Sentinel CSI Volume Object](#sentinel-csi-volume-objects). - `volume_exists`: a boolean field that indicates that a previous version of the volume exists. - `nomad_acl_token`: the ACL token the job was submitted with. This is a [Sentinel Nomad ACL Token Object](#sentinel-acl-token-objects). - `namespace`: the namespace the job is in. This is a [Sentinel Nomad Namespace Object](#sentinel-namespace-objects). Sentinel convention for identifiers is lower case and separated by underscores. All fields on an object are accessed by the same name, converted to lower case and separating camel case to underscores. ## Sentinel Job Objects The `job` and `existing_job` objects map to the [JSON job specification][], with the fields converted to the Sentinel convention. Here are some examples: | Job Field | Sentinel Accessor | |------------------------------------------|---------------------------------------------| | `job.ID` | `job.id` | | `job.AllAtOnce` | `job.all_at_once` | | `job.ParentID` | `job.parent_id` | | `job.TaskGroups` | `job.task_groups` | | `job.TaskGroups[0].EphemeralDisk.SizeMB` | `job.task_groups[0].ephemeral_disk.size_mb` | ## Sentinel ACL Token Objects The `nomad_acl_token` object maps to the [ACL token][], with the fields converted to the Sentinel convention. Here are some examples: | Nomad ACL Token Field | Sentinel Accessor | |-------------------------------|-------------------------------| | `nomad_acl_token.AccessorID` | `nomad_acl_token.accessor_id` | | `nomad_acl_token.Policies[0]` | `nomad_acl_token.policies[0]` | Note that the `SecretID` field is always redacted to prevent credential leaks. ## Sentinel Namespace Objects The `namespace` object maps to the [Namespace][], with the fields converted to the Sentinel convention. Here are some examples: | Namespace Field | Sentinel Accessor | |----------------------------------------------|------------------------------------------------| | `namespace.Description` | `namespace.description` | | `namespace.NodePoolConfiguration.Allowed[0]` | `namespace.node_pool_configuration.allowed[0]` | ## Sentinel Node Objects The `node` object maps to the [Node][], with the fields converted to the Sentinel convention. Here are some examples: | Node Field | Sentinel Accessor | |--------------------|--------------------| | `node.Class` | `node.class` | | `node.Meta["foo"]` | `node.meta["foo"]` | ## Sentinel Node Pool Objects The `node_pool` object maps to the [Node Pool][], with the fields converted to the Sentinel convention. Here are some examples: | Node Pool Field | Sentinel Accessor | |-------------------------------------------------------|---------------------------------------------------------| | `node_pool.Description` | `node_pool.description` | | `node_pool.SchedulerConfiguration.SchedulerAlgorithm` | `node_pool.scheduler_configuration.scheduler_algorithm` | ## Sentinel Dynamic Host Volume Objects The `volume` object maps to the [Dynamic Host Volume][], with the fields converted to the Sentinel convention. Here are some examples: | Dynamic Host Volume Field | Sentinel Accessor | |----------------------------------------------|------------------------------------------------| | `volume.Name` | `volume.name` | | `volume.RequestedCapabilities[0].AccessMode` | `volume.requested_capabilities[0].access_mode` | ## Sentinel CSI Volume Objects The `volume` object maps to the [CSI Volume][], with the fields converted to the Sentinel convention. Here are some examples: | CSI Volume Field | Sentinel Accessor | |----------------------------------------------|------------------------------------------------| | `volume.Name` | `volume.name` | | `volume.RequestedCapabilities[0].AccessMode` | `volume.requested_capabilities[0].access_mode` | Note that the `volume.Secrets` values and `volume.MountOptions.MountFlags` are always redacted to prevent credential leaks. [Nomad Sentinel Tutorial]: /nomad/docs/govern/sentinel [`nomad sentinel`]: /nomad/commands/sentinel [sentinel]: https://docs.hashicorp.com/sentinel [JSON job specification]: /nomad/api-docs/json-jobs [ACL token]: https://github.com/hashicorp/nomad/blob/v1.9.4/nomad/structs/structs.go#L13502-L13531 [Namespace]: https://github.com/hashicorp/nomad/blob/v1.9.4/nomad/structs/structs.go#L5578-L5610 [Node]: https://github.com/hashicorp/nomad/blob/v1.9.4/nomad/structs/structs.go#L2086-L2210 [Node Pool]: https://github.com/hashicorp/nomad/blob/v1.9.4/nomad/structs/node_pool.go#L46-L68 [Dynamic Host Volume]: https://github.com/hashicorp/nomad/blob/main/nomad/structs/host_volumes.go#L18-L87 [CSI Volume]: https://github.com/hashicorp/nomad/blob/main/nomad/structs/csi.go#L249-L312