vault-sync

A poor man's tool to replicate secrets from one Vault instance to another.

How it works

When vault-sync starts, it does a full copy of the secrets from the source Vault instance to the destination Vault instance. Periodically, vault-sync does a full reconciliation to make sure all the destination secrets are up to date.

At the same time, you can manually enable the Socket Audit Device for the source Vault, so Vault will be sending audit logs to vault-sync. Using these audit logs, vault-sync keeps the secrets in the destination Vault up to date. Note that vault-sync does not create or delete the audit devices by itself.

It is possible to use the same Vault instance as the source and the destination. You can use this feature to replicate a "folder" of secrets to another "folder" on the same server. You need to specify different prefixes (src.prefix and dst.prefix) in the configuration file to make sure the source and the destination do not overlap.

Limitations

• Only two Vault auth methods are supported: Token and AppRole
• Only secrets are replicated (specifically their latest versions)
• Deleting secrets is not supported

Configuration

Use the example to create your own configuration file. Instead of specifying secrets in the configuration file, you can use environment variables:

• For Token auth method:
  • VAULT_SYNC_SRC_TOKEN
  • VAULT_SYNC_DST_TOKEN
• For AppRole auth method:
  • VAULT_SYNC_SRC_ROLE_ID
  • VAULT_SYNC_SRC_SECRET_ID
  • VAULT_SYNC_DST_ROLE_ID
  • VAULT_SYNC_DST_SECRET_ID

Source Vault

A token or AppRole for the source Vault should have a policy that allows listing and reading secrets:

For KV secrets engine v1:

cat <<EOF | vault policy write vault-sync-src -
path "secret/*" {
  capabilities = ["read", "list"]
}
EOF

For KV secrets engine v2:

cat <<EOF | vault policy write vault-sync-src -
path "secret/data/*" {
  capabilities = ["read", "list"]
}
path "secret/metadata/*" {
  capabilities = ["read", "list"]
}
EOF

If the secrets engine mounted to a custom path instead of "secret", then replace "secret" above with the custom path.

To create a token for vault-sync for the source Vault:

vault token create -policy=vault-sync-src

To enable AppRole auth method and create AppRole for vault-sync for the source Vault:

# Enable approle auth method
vault auth enable approle
# Create a new approle and assign the policy
vault write auth/approle/role/vault-sync-src token_policies=vault-sync-src
# Get role id
vault read auth/approle/role/vault-sync-src/role-id
# Get secret id
vault write -f auth/approle/role/vault-sync-src/secret-id

Enabling audit log:

if you want to use the Vault audit device for vault-sync, then you need to create an audit device that always works. If you have only one audit device enabled, and it is not working (for example, vault-sync has terminated), then Vault will be unresponsive. Vault will not complete any requests until the audit device can write. If you have more than one audit device, then Vault will complete the request as long as one audit device persists the log. The simples way to create an audit device that always works:

vault audit enable -path stdout file file_path=stdout

Then, when vault-sync is running, create the audit device that will be sending audit logs to vault-sync:

vault audit enable -path vault-sync socket socket_type=tcp address=vault-sync:8202

The device name is vault-sync, use the same value as specified for id in the configuration file. For address, specify the external endpoint for vault-sync. Note that vault-sync should be running and accessible via the specified address, otherwise Vault will not create the audit device.

Destination Vault

A token or AppRole for the source Vault should have a policy that allows operations on secrets:

For KV secrets engine v1:

cat <<EOF | vault policy write vault-sync-dst -
path "secret/*" {
  capabilities = ["create", "read", "update", "delete"]
}
EOF

For KV secrets engine v2:

cat <<EOF | vault policy write vault-sync-dst -
path "secret/data/*" {
  capabilities = ["create", "read", "update", "delete"]
}
EOF

If the secrets engine mounted to a custom path instead of "secret", then replace "secret" above with the custom path.

To create a token for vault-sync for the source Vault:

vault token create -policy=vault-sync-dst

To enable AppRole auth method and create AppRole for vault-sync for the source Vault:

# Enable approle auth method
vault auth enable approle
# Create a new approle and assign the policy
vault write auth/approle/role/vault-sync-dst token_policies=vault-sync-dst
# Get role id
vault read auth/approle/role/vault-sync-dst/role-id
# Get secret id
vault write -f auth/approle/role/vault-sync-dst/secret-id

Running

vault-sync --config vault-sync.yaml

Command line options:

• --dry-run vault-sync shows all the changes it is going to make to the destination Vault, but does not do any actual changes.
• --once runs the full sync once, then exits.

Installation

From source code

cargo build --release

Docker

Assuming your configuration file vault-sync.yaml is in the current directory:

docker run -it -v $PWD:/vault-sync pbchekin/vault-sync:0.8.0 \
  vault-sync --config /vault-sync/vault-sync.yaml

Helm chart

helm repo add vault-sync https://pbchekin.github.io/vault-sync
helm search repo vault-sync
# create myvalues.yaml, using install/helm/values.yaml as the example
helm install vault-sync vault-sync/vault-sync -f myvalues.yaml