Sentinel

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.

See the Nomad Sentinel Tutorial for more information about deploying Sentinel policies, as well as the documentation for the nomad sentinel subcommands.

Sentinel Policies

Sentinel policies are specified in the Sentinel Language. 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.

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.
existing_job: the previous version of the job. If job_exists is true, this will always be non-nil. This is also a Sentinel Job Object.
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.
namespace: the namespace the job is in. This is a Sentinel Nomad Namespace Object.

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]`