Use of config API for configuring HTTP services dynamically

config-lookup.bal

import ballerina.net.http;
import ballerina.config;

const int httpPort = initPort();

@http:configuration {port:httpPort}
service<http> echo {

    @http:resourceConfig {
        path:"/"
    }
    resource echoResource (http:Connection conn, http:InRequest req) {
        http:OutResponse res = {};
        res.setStringPayload("Resource invoked");
        _ = conn.respond(res);
    }
}

function initPort() (int) {
    string portStr = config:getGlobalValue("http.port");
    int port;
    port, _ = <int>portStr;
    return port;
}