»Vault Enterprise Replication

»Overview

Note: All versions of Vault Enterprise have support for Disaster Recovery replication. Performance Replication requires the Multi-Datacenter & Scale module.

Many organizations have infrastructure that spans multiple datacenters. Vault provides the critical services of identity management, secrets storage, and policy management. This functionality is expected to be highly available and to scale as the number of clients and their functional needs increase; at the same time, operators would like to ensure that a common set of policies are enforced globally, and a consistent set of secrets and keys are exposed to applications that need to interoperate.

Vault replication addresses both of these needs in providing consistency, scalability, and highly-available disaster recovery.

Note: Using replication requires a storage backend that supports transactional updates, such as Consul.

»Architecture

The core unit of Vault replication is a cluster, which is comprised of a collection of Vault nodes (an active and its corresponding HA nodes). Multiple Vault clusters communicate in a one-to-many near real-time flow.

Replication operates on a leader/follower model, wherein a leader cluster (known as a primary) is linked to a series of follower secondary clusters. The primary cluster acts as the system of record and asynchronously replicates most Vault data.

All communication between primaries and secondaries is end-to-end encrypted with mutually-authenticated TLS sessions, setup via replication tokens which are exchanged during bootstrapping.

What data is replicated between the primary and secondary depends on the type of replication that is configured between the primary and secondary. These types of relationships are either disaster recovery or performance relationships.

»Performance Replication and Disaster Recovery (DR) Replication

Performance Replication: In performance replication, secondaries keep track of their own tokens and leases but share the underlying configuration, policies, and supporting secrets (K/V values, encryption keys for transit, etc).

If a user action would modify underlying shared state, the secondary forwards the request to the primary to be handled; this is transparent to the client. In practice, most high-volume workloads (reads in the kv backend, encryption/decryption operations in transit, etc.) can be satisfied by the local secondary, allowing Vault to scale relatively horizontally with the number of secondaries rather than vertically as in the past.

Disaster Recovery (DR) Replication: In disaster recovery (or DR) replication, secondaries share the same underlying configuration, policy, and supporting secrets (K/V values, encryption keys for transit, etc) infrastructure as the primary. They also share the same token and lease infrastructure as the primary, as they are designed to allow for continuous operations with applications connecting to the original primary on the election of the DR secondary.

DR is designed to be a mechanism to protect against catastrophic failure of entire clusters. They do not forward service read or write requests until they are elected and become a new primary.

Capability	Disaster Recovery	Performance
Mirrors the configuration of a primary cluster	Yes	Yes
Mirrors the configuration of a primary cluster’s backends (i.e.: auth methods, secrets engines, audit devices, etc.)	Yes	Yes
Mirrors the tokens and leases for applications and users interacting with the primary cluster	Yes	No. Secondaries keep track of their own tokens and leases. When the secondary is promoted, applications must reauthenticate and obtain new leases from the newly-promoted primary.
Allows the secondary cluster to handle client requests	No	Yes

For more information on the capabilities of performance and disaster recovery replication, see the Vault Replication API Documentation.

»Primary and Secondary Cluster Compatibility

»Storage engines

There is no requirement that both clusters use the same storage engine.

»Seals

There is no requirement that both clusters use the same seal type, but see sealwrap for the full details.

Also note that enabling replication will modify the secondary seal. If the secondary uses an auto seal, its recovery configuration and keys will be replaced; if it uses shamir, its seal configuration and unseal keys will be replaced. Here seal/recovery configuration means the number of seal/recovery key fragments and the required threshold of those fragments.

Primary seal	Secondary seal	Impact on secondary of enabling replication
Shamir	Shamir	Seal config and unseal keys replaced with primary's
Shamir	Auto	Seal recovery config and recovery keys replaced with primary's seal config and unseal keys
Auto	Auto	Seal recovery config and recovery keys replaced with primary's
Auto	Shamir	Seal config and unseal keys replaced with primary's recovery seal config and recovery keys

»Vault versions

Vault changes are designed and tested to ensure that the upgrade instructions are viable, i.e. that a secondary can run a newer Vault version than its primary.

That said, we do not recommend running replicated Vault clusters with different versions any longer than necessary to perform the upgrade.

»Internals

Details on the internal design of the replication feature can be found in the replication internals document.

»Security Model

Vault is trusted all over the world to keep secrets safe. As such, we have put extreme focus to detail to our replication model as well.

»Primary/Secondary Communication

When a cluster is marked as the primary it generates a self-signed CA certificate. On request, and given a user-specified identifier, the primary uses this CA certificate to generate a private key and certificate and packages these, along with some other information, into a replication bootstrapping bundle, a.k.a. a secondary activation token. The certificate is used to perform TLS mutual authentication between the primary and that secondary.

This CA certificate is never shared with secondaries, and no secondary ever has access to any other secondary’s certificate. In practice this means that revoking a secondary’s access to the primary does not allow it continue replication with any other machine; it also means that if a primary goes down, there is full administrative control over which cluster becomes primary. An attacker cannot spoof a secondary into believing that a cluster the attacker controls is the new primary without also being able to administratively direct the secondary to connect by giving it a new bootstrap package (which is an ACL-protected call).

Vault makes use of Application Layer Protocol Negotiation on its cluster port. This allows the same port to handle both request forwarding and replication, even while keeping the certificate root of trust and feature set different.

»Secondary Activation Tokens

A secondary activation token is an extremely sensitive item and as such is protected via response wrapping. Experienced Vault users will note that the wrapping format for replication bootstrap packages is different from normal response wrapping tokens: it is a signed JWT. This allows the replication token to carry the redirect address of the primary cluster as part of the token. In most cases this means that simply providing the token to a new secondary is enough to activate replication, although this can also be overridden when the token is provided to the secondary.

Secondary activation tokens should be treated like Vault root tokens. If disclosed to a bad actor, that actor can gain access to all Vault data. It should therefore be treated with utmost sensitivity. Like all response-wrapping tokens, once the token is used successfully (in this case, to activate a secondary) it is useless, so it is only necessary to safeguard it from one machine to the next. Like with root tokens, HashiCorp recommends that when a secondary activation token is live, there are multiple eyes on it from generation until it is used.

Once a secondary is activated, its cluster information is stored safely behind its encrypted barrier.

»Learn

Refer to the following tutorials replication setup and best practices:

»API

The Vault replication component has a full HTTP API. Please see the Vault Replication API for more details.