"nginx configuration is invalid" error when starting Kong with a custom template built for a different Kong version

When attempting to start Kong using a custom template the below error is observed and Kong fails to start.

Error: nginx configuration is invalid (exit code 1):
nginx: [emerg] "return" directive is not allowed here in /usr/local/kong/nginx.conf:18
nginx: configuration file /usr/local/kong/nginx.conf test failed

These errors can take similar forms, but may include slightly different wording such as:

Error: nginx configuration is invalid (exit code 1):
nginx: [emerg] unknown directive "--" in /usr/local/kong/nginx.conf:26
nginx: configuration file /usr/local/kong/nginx.conf test failed

This issue can be caused by starting Kong with a custom template that is based on a different version of Kong than the one you are running. For example, you are running Kong Gateway 3.14.0.0 and using the nginx_kong.lua from a 3.4 install to build your custom template.

As there can be changes between releases, it is important when moving between versions that you ensure your custom templates are up to date. For notes on creating a custom template, see the custom Nginx templates reference.