Configuration

The gateway configuration block is similar to a cluster block:

gateway {
    name: "A"
    listen: "localhost:7222"
    authorization {
        user: gwu
        password: gwp
    }

    gateways: [
        {name: "A", url: "nats://gwu:gwp@localhost:7222"},
        {name: "B", url: "nats://gwu:gwp@localhost:7333"},
        {name: "C", url: "nats://gwu:gwp@localhost:7444"},
    ]
}

One difference is that instead of routes you specify gateways. As expected self-gateway connections are ignored, so you can share gateway configurations with minimal fuss.

Starting a server:

> nats-server -c A.conf
[85803] 2019/05/07 10:50:55.902474 [INF] Starting nats-server version 2.0.0
[85803] 2019/05/07 10:50:55.903669 [INF] Gateway name is A
[85803] 2019/05/07 10:50:55.903684 [INF] Listening for gateways connections on localhost:7222
[85803] 2019/05/07 10:50:55.903696 [INF] Address for gateway "A" is localhost:7222
[85803] 2019/05/07 10:50:55.903909 [INF] Listening for client connections on 0.0.0.0:4222
[85803] 2019/05/07 10:50:55.903914 [INF] Server id is NBHUDBF3TVJSWCDPG2HSKI4I2SBSPDTNYEXEMOFAZUZYXVA2IYRUGPZU
[85803] 2019/05/07 10:50:55.903917 [INF] Server is ready
[85803] 2019/05/07 10:50:56.830669 [INF] 127.0.0.1:50892 - gid:2 - Processing inbound gateway connection
[85803] 2019/05/07 10:50:56.830673 [INF] 127.0.0.1:50891 - gid:1 - Processing inbound gateway connection
[85803] 2019/05/07 10:50:56.831079 [INF] 127.0.0.1:50892 - gid:2 - Inbound gateway connection from "C" (NBHWDFO3KHANNI6UCEUL27VNWL7NWD2MC4BI4L2C7VVLFBSMZ3CRD7HE) registered
[85803] 2019/05/07 10:50:56.831211 [INF] 127.0.0.1:50891 - gid:1 - Inbound gateway connection from "B" (ND2UJB3GFUHXOQ2UUMZQGOCL4QVR2LRJODPZH7MIPGLWCQRARJBU27C3) registered
[85803] 2019/05/07 10:50:56.906103 [INF] Connecting to explicit gateway "B" (localhost:7333) at 127.0.0.1:7333
[85803] 2019/05/07 10:50:56.906104 [INF] Connecting to explicit gateway "C" (localhost:7444) at 127.0.0.1:7444
[85803] 2019/05/07 10:50:56.906404 [INF] 127.0.0.1:7333 - gid:3 - Creating outbound gateway connection to "B"
[85803] 2019/05/07 10:50:56.906444 [INF] 127.0.0.1:7444 - gid:4 - Creating outbound gateway connection to "C"
[85803] 2019/05/07 10:50:56.906647 [INF] 127.0.0.1:7444 - gid:4 - Outbound gateway connection to "C" (NBHWDFO3KHANNI6UCEUL27VNWL7NWD2MC4BI4L2C7VVLFBSMZ3CRD7HE) registered
[85803] 2019/05/07 10:50:56.906772 [INF] 127.0.0.1:7333 - gid:3 - Outbound gateway connection to "B" (ND2UJB3GFUHXOQ2UUMZQGOCL4QVR2LRJODPZH7MIPGLWCQRARJBU27C3) registered

Once all the gateways are up, these clusters of one will forward messages as expected:

> nats-sub -s localhost:4333 ">"
Listening on [>]

# On a different session...
> nats-pub -s localhost:4444 foo bar
Published [foo] : 'bar'

# nats-sub should print 
[#1] Received on [foo] : 'bar'

Gateway Configuration Block

Property	Description
name	Name for this cluster, all gateways belonging to the same cluster, should specify the same name.
reject_unknown	If true, gateway will reject connections from gateways that are not configured in gateways.
gateways	List of Gateway entries - see below.
host	Interface where the gateway will listen for incoming gateway connections.
port	Port where the gateway will listen for incoming gateway connections.
listen	Combines host and port as <host>:<port>
tls	A tls configuration map for securing gateway connections. verify is always enabled. Unless otherwise specified in a gateway, cert_file will be the default client certificate. See for certificate pitfalls.
advertise	Hostport <host>:<port> to advertise how this server can be contacted by other gateway members. This is useful in setups with NAT.
connect_retries	After how many failed connect attempts to give up establishing a connection to a discovered gateway. Default is 0, do not retry. When enabled, attempts will be made once a second. This, does not apply to explicitly configured gateways.
authorization	Authorization map for gateways. When token or a single username/password are used, they define the authentication mechanism this server expects. What authentication values other server have to provide when connecting. They also specify how this server will authenticate itself when establishing a connection to a discovered gateway. This will not be used for gateways explicitly listed in gateways and therefore have to be provided as part of the URL. If you use token or password based authentication, either use the same credentials throughout the system or list every gateway explicitly on every server. If the tls configuration map specifies verify_and_map only provide the expected username. Here different certificates can be used, but they do have to map to the same username. The authorization map also allows for timeout which is honored but users and permissions are ignored.

Gateway Entry

The gateways configuration block is a list of gateway entries with the following properties:

Property	Description
name	Gateway name.
url	Hostport <host>:<port> describing where the remote gateway can be reached. If multiple IPs are returned, one is randomly selected.
urls	A list of url strings.
tls	A tls configuration map for creating a secure gateway connection. If the top-level gateway{} tls block contains certificates that have both client and server purposes, it is possible to omit this one and the server will use the certificates from the gateway{tls{}} section.

By using urls and an array, you can specify a list of endpoints that form part of a cluster as below. A NATS Server will pick one of those addresses randomly and only establish a single outbound gateway connection to one of the members from another cluster:

gateway {
    name: "DC-A"
    listen: "localhost:7222"

    gateways: [
        {name: "DC-A", urls: ["nats://localhost:7222", "nats://localhost:7223", "nats://localhost:7224"]},
        {name: "DC-B", urls: ["nats://localhost:7332", "nats://localhost:7333", "nats://localhost:7334"]},
        {name: "DC-C", urls: ["nats://localhost:7442", "nats://localhost:7333", "nats://localhost:7335"]}
    ]
}