Support for non-webapps and/or non-actuator apps

[dsyer]

Currently we try to determine the "endpoint" (in Zipkin terms but the code is in core) by looking at ServerProperties. What if there isn't one? Maybe the ApplicationContext id is a good enough replacement?

[spencergibb]

Endpoint takes three params:

1. ipv4: we can in the worst case use non-loopback lookup ala Move non-loopback address lookup to commons spring-cloud-commons#47
2. port: 0?
3. servicename: if spring.application.name isn't set, we could use ApplicationContext id

[dsyer]

I think this is superseded by the *Locator interfaces we provided. The only problem is that we default to span.getProcessId() if it is not-null (which might have very little to do with the actual service name).

[marcingrzejszczak]

Currently if ServerProperties is null the code will provide defaults:

public class ServerPropertiesEndpointLocator implements EndpointLocator {

    private final ServerProperties serverProperties;
    private final String appName;
    private Integer port;

    public ServerPropertiesEndpointLocator(ServerProperties serverProperties,
                                                                                String appName) {
        this.serverProperties = serverProperties;
        this.appName = appName;
    }

    @Override
    public Endpoint local() {
        int address = getAddress();
        Integer port = getPort();
        return Endpoint.create(this.appName, address, port);
    }

    @EventListener(EmbeddedServletContainerInitializedEvent.class)
    public void grabPort(EmbeddedServletContainerInitializedEvent event) {
        this.port = event.getEmbeddedServletContainer().getPort();
    }

    private Integer getPort() {
        if (this.port!=null) {
            return this.port;
        }
        Integer port;
        if (this.serverProperties!=null && this.serverProperties.getPort() != null) {
            port = this.serverProperties.getPort();
        }
        else {
            port = 8080;
        }
        return port;
    }

    private int getAddress() {
        if (this.serverProperties!=null && this.serverProperties.getAddress() != null) {
            return InetUtils.getIpAddressAsInt(this.serverProperties.getAddress().getHostAddress());
        }
        else {
            return 127 << 24 | 1;
        }
    }
}

so theoretically the code works without ServerProperties - even though it returns some arbitrary values