Configuration

leafnodes Configuration Block

The leaf node configuration block is used to configure incoming as well as outgoing leaf node connections. Most properties are for the configuration of incoming connections. The properties remotes and reconnect are for outgoing connections.

Property	Description
host	Interface where the server will listen for incoming leafnode connections.
port	Port where the server will listen for incoming leafnode connections (default is 7422).
listen	Combines host and port as <host>:<port>
tls	TLS configuration block (same as other nats-server tls configuration).
advertise	Hostport <host>:<port> to advertise how this server can be contacted by leaf nodes. This is useful in cluster setups with NAT.
no_advertise	if true the server shouldn't be advertised to leaf nodes.
authorization	Authorization block. See Authorization Block section below.
remotes	List of remote entries specifying servers where leafnode client connection can be made.
reconnect	Interval in seconds at which reconnect attempts to a remote server are made.
compression	Configures compression of leafnode connections similar to cluster routes. Defaults to s2_auto. See details here.

TLS Block

As of NATS v2.10.0

The tls block for leafnodes configuration has an additional field enabling a TLS-first handshake between the remote and the accepting server.

Property	Description
handshake_first	If true on the accepting side, remote leafnodes are required to also have this setting configured in the remotes section.

Accepting side

Since Leafnodes can connect to a variety of servers, the ability to indicate if the TLS handshake should be done first is configured in 2 places. The accepting side is in the tls block of the leafnodes block.

leafnodes {
  port: 7422
  tls {
    handshake_first: true
    # other TLS fields...
  }
}

With the above configuration, an older server, or a server that does not have the remote configuration also configured with handshake_first: true, will fail to create a leafnode connection because the accepting-side server will initiate the TLS handshake while the soliciting side will wait for the INFO protocol to be received.

Remote side

To indicate that a leafnode connection should perform the TLS handshake first, it needs to be configured in the remote configuration:

leafnodes {
  remotes [
    {
      urls: ["tls://example:7422"]
      tls: {
         handshake_first: true
         # other TLS fields...
      }
    }
  ]
}

If the remote is configured as such but the server it is connecting to does not have handshake_first: true configured, the connection will fail since the solicit side is performing a TLS handshake but will receive an INFO protocol in clear.

Authorization Block

A leaf node can authenticate against any user account on the hub (the incoming side of the connection), including those defined in the accounts themselves. This authorization block is therefore optional if appropriate account users already exist.

Whether configuring users in the account or in this dedicated authorization block is more convenient will depend on your deployment style.

Property	Description
user	Username for the leaf node connection.
password	Password for the user entry.
account	Account this leaf node connection should be bound to.
timeout	Maximum number of seconds to wait for leaf node authentication.
users	List of credentials and account to bind to leaf node connections. See User Block section below.

Users Block

Property	Description
user	Username for the leaf node connection.
password	Password for the user entry.
account	Account this leaf node connection should be bound to.

Here are some examples of using basic user/password authentication for leaf nodes (note while this is using accounts it is not using JWTs)

Singleton mode:

leafnodes {
  port: ...
  authorization {
    user: leaf
    password: secret
    account: TheAccount
  }
}

With above configuration, if a soliciting server creates a Leafnode connection with url: nats://leaf:secret@host:port, then the accepting server will bind the leafnode connection to the account "TheAccount". This account needs to exist otherwise the connection will be rejected.

Multi-users mode:

leafnodes {
  port: ...
  authorization {
    users = [
      {user: leaf1, password: secret, account: account1}
      {user: leaf2, password: secret, account: account2}
    ]
  }
}

With the above, if a server connects using leaf1:secret@host:port, then the accepting server will bind the connection to account account1. If using leaf2 user, then the accepting server will bind to connection to account2.

If username/password (either singleton or multi-users) is defined, then the connecting server MUST provide the proper credentials otherwise the connection will be rejected.

If no username/password is provided, it is still possible to provide the account the connection should be associated with:

leafnodes {
  port: ...
  authorization {
    account: TheAccount
  }
}

With the above, a connection without credentials will be bound to the account "TheAccount".

If other form of credentials are used (jwt, nkey or other), then the server will attempt to authenticate and if successful associate to the account for that specific user. If the user authentication fails (wrong password, no such user, etc..) the connection will be also rejected.

LeafNode remotes Entry Block

Property	Description
url	Leafnode URL (URL protocol should be nats-leaf).
urls	Leafnode URL array. Supports multiple URLs for discovery, e.g., urls: [ "nats-leaf://host1:7422", "nats-leaf://host2:7422" ]
no_randomize	IF true, always try connecting in sequence on the URLs in the list. Default behavior if to shuffle the URLs and start connection attempts with a random URL
account	Account name or JWT public key identifying the local account to bind to this remote server. Any traffic locally on this account will be forwarded to the remote server.
deny_imports	List of subjects which will not be imported over this leaf node connection. Subscriptions to those subjects will not be propagated to the hub.
deny_exports	List of subjects which will not be exported over this leaf node connection. Subscriptions to those subjects will not be propagated into the leaf node.
credentials	Credential file for connecting to the leafnode server.
nkey	Nkey used for connecting to the leafnode server.
tls	A TLS configuration block. Leafnode client will use specified TLS certificates when connecting/authenticating.
ws_compression	If connecting with Websocket protocol, this boolean (true or false) indicates to the remote server that it wishes to use compression. The default is false.
ws_no_masking	If connecting with Websocket protocol, this boolean indicates to the remote server that it wishes not to mask outbound WebSocket frames. The default is false, which means that outbound frames will be masked.
compression	Configures compression of leafnode connections similar to cluster routes. Defaults to s2_auto. See details here.
hub	Default is false. If set to true the roles of leaf node and hub will be reversed. This allows the hub to initiate a leaf node connection to the leaf.
first_info_timeout	Default 1s. The first information sent back by the hub (incoming side) will be the server metadata. The client will only wait first_info_timeout before giving up. This is useful if there is the change that the port on the other side is not a NATS server or not a port accepting leaf node connection. In this case the client would wait forever for the metadata.

Signature Handler

As of NATS Server v.2.9.0, for users embedding the NATS Server, it is possible to replace the use of the credentials file by a signature callback which will sign the nonce and provide the JWT in the CONNECT protocol. The RemoteLeafOpts has a new field:

SignatureCB  SignatureHandler

The callback definition is:

// SignatureHandler is used to sign a nonce from the server while
// authenticating with Nkeys. The callback should sign the nonce and
// return the JWT and the raw signature.
type SignatureHandler func([]byte) (string, []byte, error)

And example of how to use it can be found here

Connecting using WebSocket protocol

Since NATS 2.2.0, Leaf nodes support outbound WebSocket connections by specifying ws as the scheme component of the remote server URLs:

leafnodes {
  remotes [
    {urls: ["ws://hostname1:443", "ws://hostname2:443"]}
  ]
}

Note that if a URL has the ws scheme, all URLs the list must be ws. You cannot mix and match. Therefore this would be considered an invalid configuration:

  remotes [
    # Invalid configuration that will prevent the server from starting
    {urls: ["ws://hostname1:443", "nats://hostname2:7422"]}
  ]

Note that the decision to make a TLS connection is not based on wss:// (as opposed to ws://) but instead in the presence of a TLS configuration in the leafnodes{} or the specific remote configuration block.

To configure Websocket in the remote server, check the Websocket section.

tls Configuration Block

Property	Description
cert_file	TLS certificate file.
key_file	TLS certificate key file.
ca_file	TLS certificate authority file.
insecure	Skip certificate verification.
verify	If true, require and verify client certificates.
verify_and_map	If true, require and verify client certificates and use values map certificate values for authentication purposes.
cipher_suites	When set, only the specified TLS cipher suites will be allowed. Values must match golang version used to build the server.
curve_preferences	List of TLS cypher curves to use in order.
timeout	TLS handshake timeout in fractional seconds.