New beat info: ephemeral_id

[kvch]

New "metric" is added: beat.info.ephemeral_id. I am open to alternative names for this.
This ID is generated every time the Beat starts/restarts. It does not change when the config is reloaded.

I also added strConsts list which contains strings which should be added to the monitoring events even if it is unchange. This solution is the same as the current gauges list.

[ph]

I've looked through the conditionals here, do we need a special logic for that value?
On the first run, the value of the variable s for the UUID won't be found in the delta.Strings so it will be added and the next runs will never change that value.

[ph]

Actually, we don't need that change because we never do delta on string we just need to return the current value we don't need to add any special logic to handle strings constants, because once they are set they will be immutable unless we manually change that value.

This is good finding @kvch! when we refactor the gauge we will also need an Immutable gauge type or something similar.

[ph]

even if not necessary we might want to add it to the gauge list defined in this file.

[kvch]

My solution is temporary, until gauges are refactored. I created a separate list, because it is not really a gauge, but a string constant. I am not sure what changes you are requesting.

[ph]

My point was, adding this code will result in the same behavior as before. The code present in the if and the else if part of the conditionals are exactly the same. I was challenging the need to add this logic and the current need to differentiate a static gauge and a strconstant before we have a concrete type in our system that will take care of the inherent difference between the two.

[kvch]

The first if checks if the value whether the value is constant or not. If it is constant, it is added to the delta.Strings list. The else if part checks if it is the first time it shows up in the string metrics or it is changed since the last sample, it is also added. If it hasn't changed since the last sample it does not show up.

In other words the first if checks if the string is in strConsts. The second if checks if the string was in the previous sample or if it has changed since the previous sample. Adding this code definitely changes the behavior of a Beat, as before I added this code ephemeral_id showed up only in the first event. The events after that did not include this info.

I don't want to mix string constants into gauges. Gauges go into a different lists which include numerical values delta.Ints or delta.Floats. Different types of metrics are already handled differently here, see delta.Ints, delta.Floats and delta.Strings`.

[ph]

In other words the first if checks if the string is in strConsts. The second if checks if the string was in the previous sample or if it has changed since the previous sample. Adding this code definitely changes the behavior of a Beat, as before I added this code ephemeral_id showed up only in the first event. The events after that did not include this info.

Good point

[exekias]

Would instance_id look nicer? I'm not quite sure, It may be misleading

[ph]

@exekias I think we should stay with the ephemeral_id, this is what ES and Logstash are using for the lifetime UUID.

edited, added reference
https://www.elastic.co/guide/en/elasticsearch/reference/current/cat-thread-pool.html#_other_fields

elastic/logstash#7407

[exekias]

Good point, forget about my message then 😇

[ph]

LGTM, thanks @kvch!