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Vault Integration

Many workloads require access to tokens, passwords, certificates, API keys, and other secrets. To enable secure, auditable and easy access to your secrets, Nomad integrates with HashiCorp's Vault. Nomad servers and clients coordinate with Vault to derive a Vault token that has access to only the Vault policies the tasks needs. Nomad clients make the token available to the task and handle the tokens renewal. Further, Nomad's template block can retrieve secrets from Vault making it easier than ever to secure your infrastructure.

Note that in order to use Vault with Nomad, you will need to configure and install Vault separately from Nomad. Nomad does not run Vault for you.

Note: Vault integration requires Vault version 0.6.2 or higher.

Vault Configuration

To use the Vault integration, Nomad servers must be provided a Vault token. This token can either be a root token or a periodic token with permissions to create from a token role. The root token is the easiest way to get started, but we recommend a token role based token for production installations. Nomad servers will renew the token automatically. Note that the Nomad clients do not need to be provided with a Vault token.

Root Token Integration

If Nomad is given a root token, no further configuration is needed as Nomad can derive a token for jobs using any Vault policies.

Token Role based Integration

Vault's Token Authentication Backend supports a concept called "roles". Token roles allow policies to be grouped together and token creation to be delegated to a trusted service such as Nomad. By creating a token role, the set of policies that tasks managed by Nomad can access may be limited compared to giving Nomad a root token. Token roles allow both white-list and blacklist management of policies accessible to the role.

To configure Nomad and Vault to create tokens against a role, the following must occur:

  1. Create a "nomad-server" policy used by Nomad to create and manage tokens.

  2. Create a Vault token role with the configuration described below.

  3. Configure Nomad to use the created token role.

  4. Give Nomad servers a periodic token with the "nomad-server" policy created above.

Required Vault Policies

The token Nomad receives must have the capabilities listed below. An explanation for the use of each capability is given.

# Allow creating tokens under "nomad-cluster" token role. The token role name
# should be updated if "nomad-cluster" is not used.
path "auth/token/create/nomad-cluster" {
  capabilities = ["update"]
}

# Allow looking up "nomad-cluster" token role. The token role name should be
# updated if "nomad-cluster" is not used.
path "auth/token/roles/nomad-cluster" {
  capabilities = ["read"]
}

# Allow looking up the token passed to Nomad to validate # the token has the
# proper capabilities. This is provided by the "default" policy.
path "auth/token/lookup-self" {
  capabilities = ["read"]
}

# Allow looking up incoming tokens to validate they have permissions to access
# the tokens they are requesting. This is only required if
# `allow_unauthenticated` is set to false.
path "auth/token/lookup" {
  capabilities = ["update"]
}

# Allow revoking tokens that should no longer exist. This allows revoking
# tokens for dead tasks.
path "auth/token/revoke-accessor" {
  capabilities = ["update"]
}

# Allow checking the capabilities of our own token. This is used to validate the
# token upon startup.
path "sys/capabilities-self" {
  capabilities = ["update"]
}

# Allow our own token to be renewed.
path "auth/token/renew-self" {
  capabilities = ["update"]
}

The above nomad-server policy is available for download. Below is an example of writing this policy to Vault:

# Download the policy
$ curl https://nomadproject.io/data/vault/nomad-server-policy.hcl -O -s -L

# Write the policy to Vault
$ vault policy write nomad-server nomad-server-policy.hcl

Vault Token Role Configuration

A Vault token role must be created for use by Nomad. The token role can be used to manage what Vault policies are accessible by jobs submitted to Nomad. The policies can be managed as a whitelist by using allowed_policies in the token role definition or as a blacklist by using disallowed_policies.

If using allowed_policies, tasks may only request Vault policies that are in the list. If disallowed_policies is used, task may request any policy that is not in the disallowed_policies list. There are trade-offs to both approaches but generally it is easier to use the blacklist approach and add policies that you would not like tasks to have access to into the disallowed_policies list.

An example token role definition is given below:

{
  "disallowed_policies": "nomad-server",
  "token_explicit_max_ttl": 0,
  "name": "nomad-cluster",
  "orphan": true,
  "token_period": 259200,
  "renewable": true
}
Token Role Requirements

Nomad checks that token role has an appropriate configuration for use by the cluster. Fields that are checked are documented below as well as descriptions of the important fields. See Vault's Token Authentication Backend documentation for all possible fields and more complete documentation.

  • allowed_policies - Specifies the list of allowed policies as a comma-separated string. This list should contain all policies that jobs running under Nomad should have access to.

  • disallowed_policies - Specifies the list of disallowed policies as a comma-separated string. This list should contain all policies that jobs running under Nomad should not have access to. The policy created above that grants Nomad the ability to generate tokens from the token role should be included in list of disallowed policies. This prevents tokens created by Nomad from generating new tokens with different policies than those granted by Nomad.

    A regression occurred in Vault 0.6.4 when validating token creation using a token role with disallowed_policies such that it is not usable with Nomad. This was remedied in 0.6.5 and does not effect earlier versions of Vault.

  • token_explicit_max_ttl - Specifies the max TTL of a token. Must be set to 0 to allow periodic tokens.

  • name - Specifies the name of the policy. We recommend using the name nomad-cluster. If a different name is chosen, replace the token role in the above policy.

  • orphan - Specifies whether tokens created against this token role will be orphaned and have no parents. Nomad does not enforce the value of this field but understanding the implications of each value is important.

    If set to false, all tokens will be revoked when the Vault token given to Nomad expires. This makes it easy to revoke all tokens generated by Nomad but forces all Nomad servers to use the same Vault token, even through upgrades of Nomad servers. If the Vault token that was given to Nomad and used to generate a tasks token expires, the token used by the task will also be revoked which is not ideal.

    When set to true, the tokens generated for tasks will not be revoked when Nomad's token is revoked. However Nomad will still revoke tokens when the allocation is no longer running, minimizing the lifetime of any task's token. With orphaned enabled, each Nomad server may also use a unique Vault token, making bootstrapping and upgrading simpler. As such, setting orphan = true is the recommended setting.

  • token_period - Specifies the length the TTL is extended by each renewal in seconds. It is suggested to set this value on the order of magnitude of 3 days (259200 seconds) to avoid a large renewal request rate to Vault. Must be set to a positive value.

  • renewable - Specifies whether created tokens are renewable. Must be set to true. This allows Nomad to renew tokens for tasks.

The above nomad-cluster token role is available for download. Below is an example of writing this role to Vault:

# Download the token role
$ curl https://nomadproject.io/data/vault/nomad-cluster-role.json -O -s -L

# Create the token role with Vault
$ vault write /auth/token/roles/nomad-cluster @nomad-cluster-role.json

Example Configuration

To make getting started easy, the basic nomad-server policy and nomad-cluster role described above are available for download.

The below example assumes Vault is accessible, unsealed and the operator has appropriate permissions.

# Download the policy and token role
$ curl https://nomadproject.io/data/vault/nomad-server-policy.hcl -O -s -L
$ curl https://nomadproject.io/data/vault/nomad-cluster-role.json -O -s -L

# Write the policy to Vault
$ vault policy write nomad-server nomad-server-policy.hcl

# Create the token role with Vault
$ vault write /auth/token/roles/nomad-cluster @nomad-cluster-role.json

Retrieving the Token Role based Token

After the token role is created, a token suitable for the Nomad servers may be retrieved by issuing the following Vault command:

$ vault token create -policy nomad-server -period 72h -orphan
Key             Value
---             -----
token           f02f01c2-c0d1-7cb7-6b88-8a14fada58c0
token_accessor  8cb7fcb3-9a4f-6fbf-0efc-83092bb0cb1c
token_duration  259200s
token_renewable true
token_policies  [default nomad-server]

The -orphan flag is included when generating the Nomad server token above to prevent revocation of the token when its parent expires. Vault typically creates tokens with a parent-child relationship. When an ancestor token is revoked, all of its descendant tokens and their associated leases are revoked as well.

When generating Nomad's Vault token, we need to ensure that revocation of the parent token does not revoke Nomad's token. To prevent this behavior we specify the -orphan flag when we create the Nomad's Vault token. All other tokens generated by Nomad for jobs will be generated using the policy default of orphan = false.

More information about creating orphan tokens can be found in Vault's Token Hierarchies and Orphan Tokens documentation.

The token can then be set in the server configuration's vault stanza, as a command-line flag, or via an environment variable.

$ VAULT_TOKEN=f02f01c2-c0d1-7cb7-6b88-8a14fada58c0 nomad agent -config /path/to/config

An example of what may be contained in the configuration is shown below. For complete documentation please see the Nomad agent Vault integration configuration.

vault {
  enabled          = true
  ca_path          = "/etc/certs/ca"
  cert_file        = "/var/certs/vault.crt"
  key_file         = "/var/certs/vault.key"
  address          = "https://vault.service.consul:8200"
  create_from_role = "nomad-cluster"
}

Agent Configuration

To enable Vault integration, please see the Nomad agent Vault integration configuration.

Vault Definition Syntax

To configure a job to retrieve Vault tokens, please see the vault job specification documentation.

Troubleshooting

Invalid Vault token

Upon startup, Nomad will attempt to connect to the specified Vault server. Nomad will lookup the passed token and if the token is from a token role, the token role will be validated. Nomad will not shutdown if given an invalid Vault token, but will log the reasons the token is invalid and disable Vault integration.

Permission Denied errors

If you are using a Vault version less than 0.7.1 with a Nomad version greater than or equal to 0.6.1, you will need to update your task's policy (listed in the vault stanza of the job specification) to add the following:

path "sys/leases/renew" {
    capabilities = ["update"]
}

This is included in Vault's "default" policy beginning with Vault 0.7.1 and is relied upon by Nomad's Vault integration beginning with Nomad 0.6.1. If you're using a newer Nomad version with an older Vault version, your default policy may not automatically include this and you will see "permission denied" errors in your Nomad logs similar to the following:

Code: 403. Errors:
URL: PUT https://vault:8200/v1/sys/leases/renew
* permission denied

No Secret Exists

Vault has two APIs for secrets, v1 and v2. Each version has different paths, and Nomad does not abstract this for you. As such you will need to specify the path as reflected by Vault's HTTP API, rather than the path used in the vault kv command.

You can see examples of v1 and v2 syntax in the template documentation.