Flink web UI: Monitor Metrics doesn't work

Question

run with flink-1.9.0 on yarn(2.6.0-cdh5.11.1), but the flink web ui metrics does'nt work, as shown below:

Answer 1

I guess you are looking at the wrong metrics. Due no data flows from one task to another (you can see only one box at the UI) there is nothing to show. The metrics you are looking at only show the data which flows from one flink task to another. At your example everything happens within this task.

Look at this example:

You can see two tasks sending data to the map-task which emits this data to another task. Therefore you see incoming and outgoing data.

But on the other hand a source task never has incoming data(I must admit that this is confusing at the first look):

The number of records recieved is 0 but it send a couple of records to the downstream task.

Back to your problem: What you can do is have a look at the operator metrics. If you look at the metrics tab (the one at the very right) you can select beside the task metrics also some operator metrics. These metrics have a name like 0.Map.numRecordsIn .

The name assembles like this <slot>.<operatorName>.<metricsname> . But be aware that this metrics are not recorded, you don't have any historic data and once you leave this tab or remove a metric the data collected until that point are gone. I would recommend to use a proper metrics backend like influx, prometheus or graphite. You can find a description at the flink docs .

Hope that helped.