fix(service): explicitly set user in systemd definition

[hanshuebner]

Summary

Previously, no User clause was present in the systemd unit definition for Kong. While this still made systemd run kong under the 'root' user id, the HOME environment variable would not be set in the Kong process. This caused the datafile library to fail with various error conditions. This really is an EE-only issue at this point, but providing Kong a complete run environment with all standard environment variables is prudent for CE as well.

Checklist

• The Pull Request has tests
• There's an entry in the CHANGELOG
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

KAG-1832

[bungle]

@fffonion could you take a look at this too? You probably have more context? E.g. what if someone wants to run this with other user? Ever a case? Is there anything implicit about it?

[fffonion]

I think when User= is omitted, systemd uses root by default (ref: https://www.freedesktop.org/software/systemd/man/systemd.exec.html#User=) @hanshuebner could you explain more context on why does this change fix the datafile issue?

[hanshuebner]

I think when User= is omitted, systemd uses root by default (ref: https://www.freedesktop.org/software/systemd/man/systemd.exec.html#User=) @hanshuebner could you explain more context on why does this change fix the datafile issue?

When User= is omitted, the process is indeed run as root, but having a User= specification causes the user environment to be initialized, and in particular the HOME directory was assumed to be set by datafile and absence caused versions older than 0.10 to fail silently. This PR is really just a safeguard to make sure that we always have a valid HOME environment variable. I tried to find documentation or sourcecode evidence of the behavior of systemd, but eventually gave up.