Support for multiple configuration files

[FileGo]

This adds support for multiple configuration files (in a single directory), as proposed in #512.

[FileGo]

Interesting, test fails on something that hasn't been changed.

@0xERR0R Any ideas?

[codecov]

Codecov Report

Merging #534 (3fb5ebb) into development (8d0bd8e) will decrease coverage by 0.21%.
The diff coverage is 63.63%.

@@               Coverage Diff               @@
##           development     #534      +/-   ##
===============================================
- Coverage        93.73%   93.51%   -0.22%     
===============================================
  Files               36       36              
  Lines             3112     3131      +19     
===============================================
+ Hits              2917     2928      +11     
- Misses             145      149       +4     
- Partials            50       54       +4     

Impacted Files	Coverage Δ
config/config.go	94.87% <61.90%> (-3.27%)	⬇️
cmd/root.go	58.53% <100.00%> (ø)

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[0xERR0R]

Interesting, test fails on something that hasn't been changed.

@0xERR0R Any ideas?

Is a flaky test which I can't reproduce locally ;(

[0xERR0R]

I created an issue to track it: #537

[0xERR0R]

Thanks for your work! If I understand your idea right, splitted files should contain distinct part of the target YAML. I mean, basically, all YAMLs in the directory will be concatenated together to a big target file. That means, there is no logical "merge" with attribute overwrite between pieces, right?

So following would (probably?) fail:
config1.yaml

upstream:
  default:
    - 5.9.164.112
    - 1.1.1.1

config2.yaml

upstream:
  someclient:
    - 1.2.3.4

I think, it can be a useful use case to separate config files per client or to split the blacklist configuration, but it could be technically difficult to merge the parts correct together (we have nested maps of maps in the config). What do you think?

Maybe we can leave it (take your implementation) but improve the documentation, so that it becomes clear that all config parts should have no overlapping. In this case it doesn't matter if the files are read in the alphabetically order or not.

[FileGo]

Exactly, current functionality assumes no parts of config will overlap and as you point out, it will fail the YAML unmarshal, if it does overlap.

I'll amend the documentation, to make it more clear.

[yunwu-jnpr]

I think it would be better to support include directive than blindly merging files under a directory.
You have much more control.