Key Management

Nomad servers maintain an encryption keyring used to encrypt Variables and sign task workload identities. The servers encrypt these data encryption keys (DEK) and store the wrapped keys in Raft.

The key encryption key (KEK) used to encrypt the DEK is controlled by the keyring provider. When using an external KMS or Vault transit encryption provider, the KEK is securely stored outside of Nomad. For the default AEAD provider, the KEK is stored in cleartext in Raft.

Under normal operations the keyring is entirely managed by Nomad, but this section provides administrators additional context around key replication and recovery.

Key Rotation

Only one key in the keyring is "active" at any given time, and all encryption and signing operations happen on the leader. Nomad automatically rotates the active encryption key every 30 days. When a key is rotated, the existing keys are marked as "inactive" but not deleted, so they can be used for decrypting previously encrypted variables and verifying workload identities for existing allocations.

If you believe key material has been compromised, you can execute nomad operator root keyring rotate -full. A new "active" key will be created and "inactive" keys will be marked "rekeying". Nomad will asynchronously decrypt and re-encrypt all variables with the new key. As each key's variables are encrypted with the new key, the old key will marked as "deprecated".

Key Decryption

When a leader is elected, the leader creates the keyring if it does not already exist. When a key is added, the new wrapped key material is replicated via Raft. As each server replicates the new key, the server starts a task to decrypt the key material. Until this task completes, the server is not able to serve requests that require this key.

Key Redaction in Raft Snapshots

The default AEAD keyring configuration stores the KEK in Raft. Raft snapshots contain the cleartext KEK. The nomad operator snapshot save command has a -redact option that removes the key material when creating a snapshot. The nomad operator snapshot redact command removes key material from an existing snapshot.

Redacting key material is not required when using an external KMS.

Legacy Keystore

Versions of Nomad prior to 1.9.0 stored only key metadata in Raft, but the encryption key material was stored in a separate file in the keystore subdirectory of the Nomad data directory. These files have the extension .nks.json. The key material in each file is wrapped in a unique key encryption key (KEK) that is not shared between servers.

Each server runs a key replication process that watches for changes to the state store and fetches the key material from the leader asynchronously, falling back to retrieving from other servers in the case where a key is written immediately before a leader election. Nomad 1.9.0 and above can replicate keys from older servers.

However, replicating keys from older servers means that to restore an older cluster from snapshot you need to also provide the keystore directory with the .nks.json key files on at least one server. The .nks.json key files are unique per server, but only one server's key files are needed to recover the cluster. Operators should continue to include these files as part of your organization's backup and recovery strategy for the cluster until the cluster is fully upgraded to Nomad 1.9.0 and at least one root_key_gc_interval has passed.

If you are recovering an older Raft snapshot onto a new cluster without running workloads, you can skip restoring the keyring and run nomad operator root keyring rotate once the servers have joined.