Connect to a cluster somebody else runs¶

Most services should do this. If a NATS cluster already exists, importing nats/server pulls a broker into your binary to reach a broker that is already running.

cli, err := client.Connect(ctx, gonats.ClientSettings{
    URL:  "nats://nats.internal:4222",
    Name: "my-service",
}, credential)

That is the entire difference from the in-process case. No server import, no client.InProcess, and everything that publishes or subscribes is unchanged.

The credential¶

The second argument is a gonats.CredentialSource — a function returning the token, resolved when the connection is made rather than carried around as a string.

func credential(p *props.Props) gonats.CredentialSource {
    return func(ctx context.Context) (string, error) {
        return vcs.SomeEstateLadder(ctx)   // env var name, keychain, literal
    }
}

This module deliberately does not compose that ladder. Precedence is the application's decision, and a library that decides it is a second statement of something the estate already states once.

nil is accepted, and should only ever be passed for an in-process server with no authentication. Anything reachable over a network wants a credential.

One target, or none¶

// Refused: nothing to connect to.
client.Connect(ctx, gonats.ClientSettings{}, nil)

// Refused: two different things.
client.Connect(ctx, gonats.ClientSettings{URL: "nats://..."}, cred, client.InProcess(srv))

Supplying both says two different things, and guessing which was meant is how a service ends up talking to a broker nobody thought it was talking to.

Reconnection¶

The default is to retry forever, two seconds apart. That is deliberate: a long-running service that gives up reconnecting has to be restarted by a person to recover from an outage it would otherwise have survived on its own.

Set MaxReconnects if your service genuinely should die instead.