Improve command line usage of Traces

[pwhelan]

Invocation from command line

I had the idea of improving the usage of tracing from the command line. To do this we would need to add support for new command line options to fluent-bit. I have two proposals, which could be combined:

bash$ fluent-bit \
	-Z					# enable tracing \
	-i dummy \ 				# input
	-o stdout -m '*' 			# output
	--trace-input dummy.0			# input to trace
	--trace-output stdout			# trace output
	--trace-output-property	format=json	# set the output format to JSON

It's way too wordy, IMO... but it works!

And a single one liner?

bash$ fluent-bit \
	-Z								# enable tracing \
	-i dummy \ 							# input
	-o stdout -m '*' 						# output
	--trace \
		"input=dummy.0 output=stdout output.format='json'"

Here we define in a single string the trace to add:

• from input dummy.0
• to an stdout
• with the property format: json

I currently have a branch with this implementation here: https://github.com/fluent/fluent-bit/tree/feat-trace-cmdline.