Flink can get metrics from source to the next operators，but can not get the total input/output metrics from web UI, which is inconvenient for user to get the records status for job.
- Upstream and downstream metrics is import for troubleshooting.
- No source input metrics, making many users considered that no kafka input at all, and Flink or Flink program might have some error. The same problem for the sink output metrics.
- For some one operator job(just source and sink in the same operator chain), user cannot see any stream metrics, unless adds an keyBy operation, which will print the source output metrics.