eBPF plugin improvements

[2opremio]

• Check that the protocol is TCP
• Support all HTTP methods
• Clear out tasks from table when they exit (required using task ids as table
  keys). A nice side effect of this is that we can tell apart tasks receiving 0
  req/second (i.e. tasks which currently aren't receiving any requests but were
  receiving requests at some point) from tasks which don't exist anymore.
  We report metrics fro the former.
• Simplify hash table key (no need to use a struct)

@paulbellamy @tomwilkie (and @dpw if he has the time) PTAL

[paulbellamy]

afaict, looks fine.

[dpw]

This approach has some major flaws if people try to make serious use of it . We discussed them the other day, so I won't go into details. I see it's in an "examples" directory, so maybe we don't intend people to use it seriously. If so , I hope the context makes its status clear.

[2opremio]

This approach has some major flaws if people try to make serious use of it . We discussed them the other day, so I won't go into details.

Does the Caveats comment in the ebpf code reflect that correctly?

[dpw]

Does the Caveats comment in the ebpf code reflect that correctly?

Yes. But very few people will look at comments in the code.

It's a question of context. So for example, if people have to build the examples themselves, it's fine.

[2opremio]

It's a question of context. So for example, if people have to build the examples themselves, it's fine.

Right. As you mentioned though, it's in the examples directory so I think it's fine. No code comments?