fluent custom plugin registration throws "Unknown output plugin" - ruby

Question

I am trying to modify an existing Fluentd plugin and use it with my customization. So I :
git cloned the plugin repo from github. git clone <url>
Edited my changes
gem build plugin.gemspec
gem install plugin.gem
Created a config mentioning the type of plugin
Ran fluentd -c <fluend_conf.conf> -vv
And I ended up getting this in fluentd log(fluent-plugin-swift is the plugin I edited and the type of the plugin is 'swift'):
2017-03-22 15:00:27 +0000 [info]: fluent/engine.rb:126:block in configure:
gem 'fluent-plugin-swift' version '0.0.1'
2017-03-22 15:00:27 +0000 [error]: fluent/supervisor.rb:369:rescue in
main_process: config error file="fluend_conf.conf" error="Unknown output plugin
'swift'. Run 'gem search -rd fluent-plugin' to find plugins"
EDIT-1: For clarifications
I have also checked the naming convention of the plugin that is to be registered.
The plugin is present in <base_dir>/lib/fluent/plugin/.
Also the name of file is out_swift.rb. And finally
inside the file, the plugin gets registered as:
Fluent::Plugin.register_output('swift', self)
Also is there any way, I can check the list of registered plugins, and the name it uses to get registered to fluend?
NOTE:
The same had previously worked for me, I had to re-do this as someone had formatted the machine I had my changes.
Please let me what is wrong in my approach?

Answer 1

The problem could be with the installation path, Please check the following, :
Type gem environment
You will get to see the INSTALLATION DIRECTORY like:
RubyGems Environment:
- RUBYGEMS VERSION: 2.6.8
- RUBY VERSION: 2.4.0 (2016-12-24 patchlevel 0) [x86_64-linux]
- INSTALLATION DIRECTORY: /usr/local/lib/ruby/gems/2.4.0
- USER INSTALLATION DIRECTORY: /root/.gem/ruby/2.4.0
- RUBY EXECUTABLE: /usr/local/bin/ruby
- EXECUTABLE DIRECTORY: /usr/local/bin
- SPEC CACHE DIRECTORY: /root/.gem/specs
- SYSTEM CONFIGURATION DIRECTORY: /usr/local/etc
- RUBYGEMS PLATFORMS:
- ruby
- x86_64-linux
Go inside the INSTALLATION DIRECTORY directory, now do
cd gem/<ur_custom_plugin>
Now check whether, your files are there or not.
If not, you got your answer.
SOLUTION:
Simply copy your files to this directory and start fluentd

Answer 2

As the above mentioned, this may related to which gem you used to install the plugin, for my case in CentOS7, the td-agent-gem as below works:
td-agent-gem install <pluginname>

Answer 3

install ruby development environment
brew install rbenv
now run fluentD from ruby environment
~/.rbenv/shims/fluentd
this refers /etc/fluent/fluent.conf
Installing the plugin from ruby environment
~/.rbenv/shims/gem install fluent-plugin-rewrite-tag-filter