Error in riemann-net when new interfaces are added

[md5]

On one of our hosts being monitored by riemann-net, we just ran into the following error after installing and starting Docker:

TypeError nil can't be coerced into Fixnum
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/bin/riemann-net:71:in `-'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/bin/riemann-net:71:in `block in tick'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/bin/riemann-net:70:in `each'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/bin/riemann-net:70:in `tick'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/lib/riemann/tools.rb:101:in `block in run'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/lib/riemann/tools.rb:99:in `loop'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/lib/riemann/tools.rb:99:in `run'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/lib/riemann/tools.rb:11:in `run'
/usr/lib/ruby/gems/2.1.0/gems/riemann-tools-0.1.8/bin/riemann-net:101:in `<top (required)>'
/usr/local/bin/riemann-net:23:in `load'
/usr/local/bin/riemann-net:23:in `<main>'

Looking at line 71 of that script as it was in version 0.1.8, it looks like the issue is that there is no check to see if a service is actually a key in @old_state before trying to calculate delta. When a new interface is added (e.g. the veth* or docker0 interfaces added when Docker is started), then the list of services in state has keys that aren't in @old_state, leading to the error we saw.

This same code is still in the riemann-net script on master. It looks like an easy fix would be to skip reporting for all services where @old_state.has_key? service is false.

[md5]

I was also wondering why the "drops" and "errs" checks are checking metric > 0 instead of delta > 0.