Integrated storage

Vault supports a number of storage options for the durable storage of Vault's information. This storage backend does not rely on any third party systems, implements high availability semantics, supports Replication features, and provides backup/restore workflows.

The option stores Vault's data on the server's filesystem and uses a consensus protocol to replicate data to each server in the cluster. More information on the internals of Integrated Storage can be found in the Integrated Storage internals documentation. Additionally, the Configuration docs can help in configuring Vault to use Integrated Storage.

The sections below go into various details on how to operate Vault with Integrated Storage.

Server-to-Server communication

Once nodes are joined to one another they begin to communicate using mTLS over Vault's cluster port. The cluster port defaults to 8201. The TLS information is exchanged at join time and is rotated on a cadence.

A requirement for Integrated Storage is that the cluster_addr configuration option is set. This allows Vault to assign an address to the node ID at join time.

Cluster membership

This section will outline how to bootstrap and manage a cluster of Vault nodes running Integrated Storage.

Integrated Storage is bootstrapped during the initialization process, and results in a cluster of size 1. Depending on the desired deployment size, nodes can be joined to the active Vault node.

Joining nodes

Joining is the process of taking an uninitialized Vault node and making it a member of an existing cluster. In order to authenticate the new node to the cluster it must use the same seal mechanism. If using a Auto Unseal the node must be configured to use the same KMS provider and Key as the cluster it's attempting to join. If using a Shamir seal the unseal keys must be provided to the new node before the join process can complete. Once a node has successfully joined, data from the active node can begin to replicate to it. Once a node has been joined it cannot be re-joined to a different cluster.

You can either join the node automatically via the config file or manually through the API (both methods described below). When joining a node, the API address of the leader node must be used. We recommend setting the api_addr configuration option on all nodes to make joining simpler.

retry_join configuration

This method enables setting one, or more, target leader nodes in the config file. When an uninitialized Vault server starts up it will attempt to join each potential leader that is defined, retrying until successful. When one of the specified leaders become active this node will successfully join. When using Shamir seal, the joined nodes will still need to be unsealed manually. When using Auto Unseal the node will be able to join and unseal automatically.

An example retry_join config can be seen below:

storage "raft" {
  path    = "/var/raft/"
  node_id = "node3"

  retry_join {
    leader_api_addr = "https://node1.vault.local:8200"
  }
  retry_join {
    leader_api_addr = "https://node2.vault.local:8200"
  }
}

Note, in each retry_join stanza, you may provide a single leader_api_addr or auto_join value. When a cloud auto_join configuration value is provided, Vault will use go-discover to automatically attempt to discover and resolve potential Raft leader addresses.

See the go-discover README for details on the format of the auto_join value.

storage "raft" {
  path    = "/var/raft/"
  node_id = "node3"

  retry_join {
    auto_join = "provider=aws region=eu-west-1 tag_key=vault tag_value=... access_key_id=... secret_access_key=..."
  }
}

By default, Vault will attempt to reach discovered peers using HTTPS and port 8200. Operators may override these through the auto_join_scheme and auto_join_port fields respectively.

storage "raft" {
  path    = "/var/raft/"
  node_id = "node3"

  retry_join {
    auto_join = "provider=aws region=eu-west-1 tag_key=vault tag_value=... access_key_id=... secret_access_key=..."
    auto_join_scheme = "http"
    auto_join_port = 8201
  }
}

Join from the CLI

Alternatively you can use the join CLI command or the API to join a node. The active node's API address will need to be specified:

$ vault operator raft join https://node1.vault.local:8200

Removing peers

Removing a peer node is a necessary step when you no longer want the node in the cluster. This could happen if the node is rotated for a new one, the hostname permanently changes and can no longer be accessed, you're attempting to shrink the size of the cluster, or for many other reasons. Removing the peer will ensure the cluster stays at the desired size, and that quorum is maintained.

To remove the peer you can issue a remove-peer command and provide the node ID you wish to remove:

$ vault operator raft remove-peer node1
Peer removed successfully!

Listing peers

To see the current peer set for the cluster you can issue a list-peers command. All the voting nodes that are listed here contribute to the quorum and a majority must be alive for Integrated Storage to continue to operate.

$ vault operator raft list-peers
Node     Address                   State       Voter
----     -------                   -----       -----
node1    node1.vault.local:8201    follower    true
node2    node2.vault.local:8201    follower    true
node3    node3.vault.local:8201    leader      true

Integrated storage and TLS

We've glossed over some details in the above sections on bootstrapping clusters. The instructions are sufficient for most cases, but some users have run into problems when using auto-join and TLS in conjunction with things like auto-scaling. The issue is that go-discover on most platforms returns IPs (not hostnames), and because the IPs aren't knowable in advance, the TLS certificates used to secure the Vault API port don't contain these IPs in their IP SANs.

Vault networking recap

Before we explore solutions to this problem, let's recapitulate how Vault nodes speak to one another.

Vault exposes two TCP ports: the API port and the cluster port.

The API port is where clients send their Vault HTTP requests.

For a single-node Vault cluster you don't worry about a cluster port as it won't be used.

When you have multiple nodes, you also need a cluster port. This is used by Vault nodes to issue RPCs to one another, e.g. to forward requests from a standby node to the active node, or when Raft is in use, to handle leader election and replication of stored data.

The cluster port is secured using a TLS certificate that the Vault active node generates internally. It's clear how this can work when not using integrated storage: every node has at least read access to storage, so once the active node has persisted the certificate, the standby nodes can fetch it, and all agree on how cluster traffic should be encrypted.

It's less clear how this works with Integrated Storage, as there is a chicken and egg problem. Nodes don't have a shared view of storage until the raft cluster has been formed, but we're trying to form the raft cluster! To solve this problem, a Vault node must speak to another Vault node using the API port instead of the cluster port.

node2 wants to join the cluster, so issues challenge API request to existing member node1
node1 replies to challenge request with (1) an encrypted random UUID and (2) seal config
node2 must decrypt UUID using seal; if using auto-unseal can do it directly, if using Shamir must wait for user to provide enough unseal keys to perform decryption
node2 sends decrypted UUID back to node1 using answer API
node1 sees node2 can be trusted (since it has seal access) and replies with a bootstrap package which includes the cluster TLS certificate and private key
node2 gets sent a raft snapshot over the cluster port

After this procedure the new node will never again send traffic to the API port. All subsequent inter-node communication will use the cluster port.

Assisted raft join techniques

The simplest option is to do it by hand: issue raft join commands specifying the explicit names or IPs of the nodes to join to. In this section we look at other TLS-compatible options that lend themselves more to automation.

Autojoin with TLS servername

As of Vault 1.6.2, the simplest option might be to specify a leader_tls_servername in the retry_join stanza which matches a DNS SAN in the certificate.

Note that names in a certificate's DNS SAN don't actually have to be registered in a DNS server. Your nodes may have no names found in DNS, while still using certificate(s) that contain this shared servername in their DNS SANs.

Autojoin but constrain CIDR, list all possible IPs in certificate

If all the vault node IPs are assigned from a small subnet, e.g. a /28, it becomes practical to put all the IPs that exist in that subnet into the IP SANs of the TLS certificate the nodes will share.

The drawback here is that the cluster may someday outgrow the CIDR and changing it may be a pain. For similar reasons this solution may be impractical when using non-voting nodes and dynamically scaling clusters.

Load balancer instead of autojoin

Most Vault instances are going to have a load balancer (LB) between clients and the Vault nodes. In that case, the LB knows how to route traffic to working Vault nodes, and there's no need for auto-join: we can just use retry_join with the LB address as the target.

One potential issue here: some users want a public facing LB for clients to connect to Vault, but aren't comfortable with Vault internal traffic egressing from the internal network it normally runs on.

Outage recovery

Quorum maintained

This section outlines the steps to take when a single server or multiple servers are in a failed state but quorum is still maintained. This means the remaining alive servers are still operational, can elect a leader, and are able to process write requests.

If the failed server is recoverable, the best option is to bring it back online and have it reconnect to the cluster with the same host address. This will return the cluster to a fully healthy state.

If this is impractical, you need to remove the failed server. Usually, you can issue a remove-peer command to remove the failed server if it's still a member of the cluster.

If the remove-peer command isn't possible or you'd rather manually re-write the cluster membership a raft/peers.json file can be written to the configured data directory.

Quorum lost

In the event that multiple servers are lost, causing a loss of quorum and a complete outage, partial recovery is still possible.

If the failed servers are recoverable, the best option is to bring them back online and have them reconnect to the cluster using the same host addresses. This will return the cluster to a fully healthy state.

If the failed servers are not recoverable, partial recovery is possible using data on the remaining servers in the cluster. There may be data loss in this situation because multiple servers were lost, so information about what's committed could be incomplete. The recovery process implicitly commits all outstanding Raft log entries, so it's also possible to commit data that was uncommitted before the failure.

See the section below on manual recovery using peers.json for details of the recovery procedure. You include only the remaining servers in the peers.json recovery file. The cluster should be able to elect a leader once the remaining servers are all restarted with an identical peers.json configuration.

Any servers you introduce later can be fresh with totally clean data directories and joined using Vault's join command.

In extreme cases, it should be possible to recover with just a single remaining server by starting that single server with itself as the only peer in the peers.json recovery file.

Manual recovery using peers.json

Using raft/peers.json for recovery can cause uncommitted Raft log entries to be implicitly committed, so this should only be used after an outage where no other option is available to recover a lost server. Make sure you don't have any automated processes that will put the peers file in place on a periodic basis.

To begin, stop all remaining servers.

The next step is to go to the configured data path of each Vault server. Inside that directory, there will be a raft/ sub-directory. We need to create a raft/peers.json file. The file should be formatted as a JSON array containing the node ID, address:port, and suffrage information of each Vault server you wish to be in the cluster:

[
  {
    "id": "node1",
    "address": "node1.vault.local:8201",
    "non_voter": false
  },
  {
    "id": "node2",
    "address": "node2.vault.local:8201",
    "non_voter": false
  },
  {
    "id": "node3",
    "address": "node3.vault.local:8201",
    "non_voter": false
  }
]

id (string: <required>) - Specifies the node ID of the server. This can be found in the config file, or inside the node-id file in the server's data directory if it was auto-generated.
address (string: <required>) - Specifies the host and port of the server. The port is the server's cluster port.

Create entries for all servers. You must confirm that servers you do not include here have indeed failed and will not later rejoin the cluster. Ensure that this file is the same across all remaining server nodes.

At this point, you can restart all the remaining servers. The cluster should be in an operable state again. One of the nodes should claim leadership and become active.

Other recovery methods

For other, non-quorum related recovery Vault's recovery mode can be used.

Autopilot

Autopilot enables automated workflows for managing Raft clusters. The current feature set includes 3 main features: Server Stabilization, Dead Server Cleanup and State API.

Server stabilization

Server stabilization helps to retain the stability of the Raft cluster by safely joining new voting nodes to the cluster. When a new voter node is joined to an existing cluster, autopilot adds it as a non-voter instead, and waits for a pre-configured amount of time to monitor it's health. If the node remains to be healthy for the entire duration of stabilization, then that node will be promoted as a voter. The server stabilization period can be tuned using server_stabilization_time (see below).

Dead server cleanup

Dead server cleanup automatically removes nodes deemed unhealthy from the Raft cluster, avoiding the manual operator intervention. This feature can be tuned using the cleanup_dead_servers, dead_server_last_contact_threshold, and min_quorum (see below).

State API

State API provides detailed information about all the nodes in the Raft cluster in a single call. This API can be used for monitoring for cluster health.

Follower health

Follower node health is determined by 2 factors.

Its ability to heartbeat to leader node at regular intervals. Tuned using last_contact_threshold (see below).
Its ability to keep up with data replication from the leader node. Tuned using max_trailing_logs (see below).

Default configuration

By default, Autopilot will be enabled with clusters using Vault 1.7+, although dead server cleanup is not enabled by default. Upgrade of Raft clusters deployed with older versions of Vault will also transition to use Autopilot automatically.

Autopilot exposes a configuration API to manage its behavior. Autopilot gets initialized with the following default values. If these default values do not meet your expected autopilot behavior, don't forget to set them to your desired values.

cleanup_dead_servers - false
- This controls whether to remove dead servers from the Raft peer list periodically or when a new server joins. This requires that min-quorum is also set.
dead_server_last_contact_threshold - 24h
- Limit on the amount of time a server can go without leader contact before being considered failed. This takes effect only when cleanup_dead_servers is set.
min_quorum - This doesn't default to anything and should be set to the expected number of voters in your cluster when cleanup_dead_servers is set as true.
- Minimum number of servers that should always be present in a cluster. Autopilot will not prune servers below this number.
max_trailing_logs - 1000
- Amount of entries in the Raft Log that a server can be behind before being considered unhealthy.
last_contact_threshold - 10s
- Limit on the amount of time a server can go without leader contact before being considered unhealthy.
server_stabilization_time - 10s
- Minimum amount of time a server must be in a healthy state before it can become a voter. Until that happens, it will be visible as a peer in the cluster, but as a non-voter, meaning it won't contribute to quorum.

~> Note: Autopilot in Vault does similar things to what autopilot does in Consul. However, the configuration in these 2 systems differ in terms of default values and thresholds; some additional parameters might also show up in Vault in comparison to Consul as well. Autopilot in Vault and Consul use different technical underpinnings requiring these differences, to provide the autopilot functionality.

Automated upgrades

Automated Upgrades lets you automatically upgrade a cluster of Vault nodes to a new version as updated server nodes join the cluster. Once the number of nodes on the new version is equal to or greater than the number of nodes on the old version, Autopilot will promote the newer versioned nodes to voters, demote the older versioned nodes to non-voters, and initiate a leadership transfer from the older version leader to one of the newer versioned nodes. After the leadership transfer completes, the older versioned non-voting nodes can be removed from the cluster.

Redundancy zones

Redundancy Zones provide both scaling and resiliency benefits by deploying non-voting nodes alongside voting nodes on a per availability zone basis. When using redundancy zones, each zone will have exactly one voting node and as many additional non-voting nodes as desired. If the voting node in a zone fails, a non-voting node will be automatically promoted to voter. If an entire zone is lost, a non-voting node from another zone will be promoted to voter, maintaining quorum. These non-voting nodes function not only as hot standbys, but also increase read scalability.

Replication

DR secondary and Performance secondary clusters have their own Autopilot configurations, managed independently of their primary.

The Autopilot API uses DR operation tokens for authorization when executed against a DR secondary cluster.

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