NoNodeAvailableException when connecting from Java

Elastic Stack Elasticsearch
1

We have a 2.3.3 cluster which works fine from Python. I need to connect to it from Java but am clearly doing something wrong. My code to create the client is

    Settings settings = Settings.settingsBuilder().put("client.transport.sniff", true).put("cluster.name", "foo").build();
    Client client = new TransportClient.Builder().settings(settings).build().addTransportAddress(new InetSocketTransportAddress(new InetSocketAddress("host", 9300)));

The host name is correct and "foo" is configured as the cluster name in the yml. When I try to do anything with the Client object I get

NoNodeAvailableException[None of the configured nodes are available: [{#transport#-1}{1.2.3.4}{host/1.2.3.4:9300}]]
        at org.elasticsearch.client.transport.TransportClientNodesService.ensureNodesAreAvailable(TransportClientNodesService.java:290)

The actual IP address in the error is correct, as is the host name.

I saw some StackOverflow posts which suggested adding network:publish_host and network:bind_host lines to the yml - they had no effect.

The ES log says

[transport ] [foo-1] publish_address {host/1.2.3.4:9300}, bound_addresses {1.2.3.4:9300}

Any ideas?

2

May be a firewall issue?
Can you telnet on port 9300 from the machine where the Java client runs?

3

It was not supposed to be blocked, but apparently it is. That was simple. Thanks!