Systemd unit declares EnvironmentFile=/etc/default/logstash but doesn't use variables

[roaksoax]

The Logstash systemd unit for Deb/RPMs declares the use of /etc/default/logstash as EnvironmentFile, but it does not use variables.

As such, any chances that the user makes in /etc/default/logstash won't take effect in the daemon.

Logstash information:

Please include the following information:

1. Logstash version (e.g. bin/logstash --version): 8.x
2. Logstash installation source: Deb/RPM
3. How is Logstash being run: systemd

Potential Solution:

This could be solved in two different ways:

1. Allow the systemd unit to read and use variables from /etc/default/logstash
2. Allow the systemd unit to use globally declared environment variables to override certain settings.