easier way to specify --gemfile option for td-agent

[ttanimichi]

Hi.

This feature request is related with #68.

fluentd can use Gemfile to specify plugins using "--gemfile" option. In production environment, we want to specify the plugins' version, repository and branch strictly, because sometimes fluent-plugins have bugs or version incompatibilities. Although we can use any version of plugin putting it into /etc/td-agent/plugin, it's difficult to automate provisioning by Chef or Ansible.

Now, td-agent can specify the fluentd's --gemfile option by setting the environment variable TD_AGENT_ARGS and PATH at /etc/sysconfig/td-agent or somewhere (but there is no documentation about this).

# /etc/sysconfig/td-agent
PATH="$PATH:/opt/td-agent/embedded/bin"
TD_AGENT_ARGS="/usr/sbin/td-agent --group td-agent --log /var/log/td-agent/td-agent.log --gemfile /etc/td-agent/Gemfile --use-v1-config"

This way is a little difficult. To use --gemfile option, you have to read the source code of /etc/init.d/td-agent and check the default value of TD_AGENT_ARGS. Besides, if you start td-agent without setting PATH like PATH="$PATH:/opt/td-agent/embedded/bin", td-agent will shutdown abnormally with no error message (That's because /opt/td-agent/embedded/bin/bundler isn't in PATH and fluentd's daemon can't start. Exit code is 127).

I think it's better for td-agent to prepare easier way to specify --gemfile option. e.g. Prepare the /etc/sysconfig/td-agent file with sample configrution in the installation process (like nginx and other many middlewares). What do you think about that?

Thanks.