Probably the most important part of network monitoring is monitoring backpressure, a situation where a system is receiving data at a higher rate than it can process. Such behaviour will result in the sender being backpressured and may be caused by two things:
– The receiver is slow.
This can happen because the receiver is backpressured itself, is unable to keep processing at the same rate as the sender, or is temporarily blocked by garbage collection, lack of system resources, or I/O.
– The network channel is slow.
Even though in such case the receiver is not (directly) involved, we call the sender backpressured due to a potential oversubscription on network bandwidth shared by all subtasks running on the same machine. Beware that, in addition to Flink’s network stack, there may be more network users, such as sources and sinks, distributed file systems (checkpointing, network-attached storage), logging, and metrics. A previous capacity planning blog post provides some more insights.
Read the whole thing. Backpressure is not a topic unique to Flink, but affects any ETL or streaming operation.