added config flag to skip collection of network protocol metrics

[datwiz]

Added config flag to system net (inputs.net) to ignore collection of protocol stats.
Provides feature requested in #3879

Required for all PRs:

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

[danielnelson]

Would you be interested in chaining down a list of protocols to the underlying call to gopsutil? Then we would have an option like protocols = ["udp", "tcp"] which eventually passes the list down to:

func ProtoCounters(protocols []string) ([]ProtoCountersStat, error) {

[datwiz]

I can have a go at that. 2 questions:

1. Would you see a protocols set option being used in place of an ignore_protocol_stats flag or in addition to a flag?
2. If the set option is in addition to the ignore flag, would you like the work added into this PR or raising a new one?

[danielnelson]

I guess we would need to have the boolean as well, otherwise we still can't disable them all and keep backwards compatibility. I was kind of hoping to avoid adding a boolean option here, since they often don't compose well as the plugin grows.

Let's scratch the idea of the protocols array, users can just use the fielddrop filtering option to achieve the same results.

[datwiz]

My apologies. I'm new to telegraf and hadn't fully appreciated the tag and filtering capabilities.
In my case, all the protocol stats are attributed to the interface=all tag.
I've been able to achieve the same filtering, without a new config flag using a tag drop section.

# # Read metrics about network interface usage
[[inputs.net]]
  ## By default, telegraf gathers stats from any up interface (excluding loopback)
  ## Setting interfaces will tell it to gather these explicit interfaces,
  ## regardless of status.
  ##
  interfaces = ["eth0"]
  [inputs.net.tagdrop]
    interface = [ "all" ]

At least for my use case, this config flag isn't required.

[danielnelson]

It hadn't occurred to me either that it would be so easy to filter. I think I will revert this change then since it is always better to have a smaller interface and we haven't had any other requests for this.

[zabudskyi]

Would you be interested in adding option to gather stats from "interface to Internet" only? It is useful in case there are many hosts with different interface naming, numbering, etc.

[danielnelson]

@zabudskyi How do you think we should pick which interfaces are to the internet?