[network_ext] adding integration

[truthbk]

What does this PR do?

Adds additional networking related metrics from /proc/net/netstat, /proc/net/snmp and /proc/net/udp under the system.net and docker.net namespaces.

Originally written by @ejholmes (DataDog/dd-agent#2864)

Motivation

The built-in network.py check doesn't give an accurate representation of TCP connection states, since it only represents the state at the time the metrics were collected. The raw metrics from /proc/net provide a much more granular and accurate view of networking.

For example, /proc/net/netstat gives a much more accurate representation for things like number of TCP connections opened, since it's a monotonically increasing counter within the Kernel.

Additional Notes

There's a similar PR open at DataDog/dd-agent#2720, but it's not Docker aware, which is a necessity for us at Remind. We've also chosen to use monotonic counters instead of rates, since that gives us a more accurate representation of how many events occurred in a time frame.

Hopefully we can combine ideas from both PR's, and get a more releasable version of this into network.py.

Note (cc @ejholmes)

Changes to the core (ie. docker_daemon), and the addition of the network utils has been removed from this PR when compared to the original. If you still wish us to consider that please feel free a specific PR for that in https://github.com/DataDog/dd-agent repo.

[irabinovitch]

@ejholmes Let us know if you need a hand with getting tests passing, etc. Feel free to stop by our office hours as well if we can help. Next one is this morning at 10:30 PT / 13:30 EST.

[stale]

This issue has been automatically marked as stale because it has not had activity in the last 60 days. It will be closed if no further activity occurs in the next two weeks. Thank you for participating in the Datadog open source community. If you need more time, or have any questions, let us know.

[stale]

This issue has been automatically marked as stale because it has not had activity in the last 60 days. It will be closed if no further activity occurs in the next two weeks. Thank you for participating in the Datadog open source community. If you need more time, or have any questions, let us know.