Whats the meaning of differnet keys in druid datasource status object?

When I open druid’s web console, I see my data sources list. When I click on status of any of those data-sources I get a JS object telling me the status of that data-source. But many times I don’t understand the meaning of many keys in that object. I tried searching for the Object description in druid’s official website but there itself I couldn’t find any help. Some of the keys in the object appear sometimes and sometimes they don’t appear. It’s all very confusing for me, can anybody please thorough some light, please?

I have a kafka topic named test-kafka which I connected to data-source test and then I clicked on the status of test data-source to which I got the following object as a response, some keys are quite obvious to understand but many of them are now known to me. I wanna know the meaning of bold keys in following objects, and also why these two keys appear sometime in the object and sometimes they are missing?
{“id”:“test”,“generationTime”:“2017-09-22T08:36:48.189Z”,“payload”:{“dataSource”:“test”,“topic”:“test-kafka”,“partitions”:1,“replicas”:1,“durationSeconds”:3600,“activeTasks”:[{“id”:“index_kafka_test-kafka7_9cdfda28f4a53f3_lpioodip”,“startingOffsets”:{“0”:0},“startTime”:“2017-09-22T08:36:24.675Z”,“remainingSeconds”:3576,“type”:“ACTIVE”,“currentOffsets”:{},“lag”:{}}],“publishingTasks”:,“latestOffsets”:{“0”:0},“minimumLag”:{},“aggregateLag”:0,“offsetsLastUpdated”:“2017-09-22T08:36:19.350Z”}}