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FoundationDB configuration for Vault backend storage

The FoundationDB storage backend is used to persist Vault's data in FoundationDB.

The backend needs to be explicitly enabled at build time, and is not available in the standard Vault binary distribution. Please refer to the documentation accompanying the backend's source in the Vault source tree.

  • High Availability – the FoundationDB storage backend supports high availability. The HA implementation relies on the clocks of the Vault nodes inside the cluster being properly synchronized; clock skews are susceptible to cause contention on the locks.

  • Community Supported – the FoundationDB storage backend is supported by the community. While it has undergone review by HashiCorp employees, they may not be as knowledgeable about the technology. If you encounter problems with them, you may be referred to the original author.

storage "foundationdb" {  api_version      = 520  cluster_file     = "/path/to/fdb.cluster"   tls_verify_peers = "I.CN=MyTrustedIssuer,I.O=MyCompany\, Inc.,I.OU=Certification Authority"  tls_ca_file      = "/path/to/ca_bundle.pem"  tls_cert_file    = "/path/to/cert.pem"  tls_key_file     = "/path/to/key.pem"  tls_password     = "PrivateKeyPassword"   path             = "vault-top-level-directory"  ha_enabled       = "true"}

foundationdb parameters

  • api_version (int) - The FoundationDB API version to use; this is a required parameter and doesn't have a default value. The minimum required API version is 520.

  • cluster_file (string) - The path to the cluster file containing the connection data for the target cluster; this is a required parameter and doesn't have a default value.

  • tls_verify_peers (string) - The peer certificate verification criteria; this parameter is mandatory if TLS is enabled. Refer to the FoundationDB TLS documentation.

  • tls_ca_file (string) - The path to the CA certificate bundle file; this parameter is mandatory if TLS is enabled.

  • tls_cert_file (string) - The path to the certificate file; specifying this parameter together with tls_key_file will enable TLS support.

  • tls_key_file (string) - The path to the key file; specifying this parameter together with tls_cert_file will enable TLS support.

  • tls_password (string) - The password needed to decrypt tls_key_file, if it is encrypted; optional. This can also be specified via the FDB_TLS_PASSWORD environment variable.

  • path (string: "vault") - The path of the top-level FoundationDB directory (using the directory layer) under which the Vault data will reside.

  • ha_enabled (string: "false") - Whether or not to enable Vault high-availability mode using the FoundationDB backend.

foundationdb tips

Cluster file

The FoundationDB client expects to be able to update the cluster file at runtime, to keep it current with changes happening to the cluster.

It does so by first writing a new cluster file alongside the current one, then atomically renaming it into place.

This means the cluster file and the directory it resides in must be writable by the user Vault is running as. You probably want to isolate the cluster file into its own directory.

Multi-version client

The FoundationDB client library version is tightly coupled to the server version; during cluster upgrades, multiple server versions will be running in the cluster, and the client must cope with that situation.

This is handled by the (primary) client library having the ability to load a different, later version of the client library to connect to a particular server; it is referred to as the multi-version client feature.

Client setup with LD_LIBRARY_PATH

If you do not use mlock, you can use LD_LIBRARY_PATH to point the linker at the location of the primary client library.

$ export LD_LIBRARY_PATH=/dest/dir/for/primary:$LD_LIBRARY_PATH$ export FDB_NETWORK_OPTION_EXTERNAL_CLIENT_DIRECTORY=/dest/dir/for/secondary$ /path/to/bin/vault ...

Client setup with RPATH

When running Vault with mlock, the Vault binary must have capabilities set to allow the use of mlock.

# setcap cap_ipc_lock=+ep /path/to/bin/vault$ getcap /path/to/bin/vault/path/to/bin/vault = cap_ipc_lock+ep

The presence of the capabilities will cause the linker to ignore LD_LIBRARY_PATH, for security reasons.

In that case, we have to set an RPATH on the Vault binary at build time to replace the use of LD_LIBRARY_PATH.

When building Vault, pass the -r /dest/dir/for/primary option to the Go linker, for instance:

$ make dev FDB_ENABLED=1 LD_FLAGS="-r /dest/dir/for/primary "

(Note the trailing space in the variable value above).

You can verify RPATH is set on the Vault binary using readelf:

$ readelf -d /path/to/bin/vault | grep RPATH 0x000000000000000f (RPATH)              Library rpath: [/dest/dir/for/primary]

With the client libraries installed:

$ ldd /path/to/bin/vault...    libfdb_c.so => /dest/dir/for/primary/libfdb_c.so (0x00007f270ad05000)...

Now run Vault:

$ export FDB_NETWORK_OPTION_EXTERNAL_CLIENT_DIRECTORY=/dest/dir/for/secondary$ /path/to/bin/vault ...
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