I generate a failure by adding a non-existent snippet to the middle of a provisioning template and then trying to "review" the template for an applicable host.

  <%= snippet "non-existent snippet" %>

   --- or even some gibberish ---

  <%= (%>

While the production.log (below) technically gives me details about what was wrong, it is not always accessible to the same users and can still be rather generic.


2019-12-23T12:53:28 [I|app|0525e2ad] Started GET "/unattended/provision?hostname=myhost.example.com" for 192.168.x.x at 2019-12-23 12:53:28 -0500
2019-12-23T12:53:28 [I|app|0525e2ad] Processing by UnattendedController#host_template as TEXT
2019-12-23T12:53:28 [I|app|0525e2ad]   Parameters: {"hostname"=>"myhost.example.com", "kind"=>"provision"}
2019-12-23T12:53:28 [I|app|0525e2ad] Current user set to admin (admin)
2019-12-23T12:53:28 [W|app|0525e2ad] Error rendering the AA_Kickstart_RHEL8 template
2019-12-23T12:53:28 [W|app|0525e2ad] Action failed
2019-12-23T12:53:28 [I|app|0525e2ad] Completed 500 Internal Server Error in 209ms (ActiveRecord: 17.6ms)
2019-12-23T12:53:28 [F|app|0525e2ad]   
2019-12-23T12:53:28 [F|app|0525e2ad] ActionView::MissingTemplate (Missing template common/500 with {:locale=>[:en], :formats=>[:text], :variants=>[], :handlers=>[:raw, :erb, :html, :builder, :ruby, :rabl]}. Searched in:
  * "/usr/share/foreman/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_inventory_upload-1.0.2/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_ansible-3.0.7.1/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_virt_who_configure-0.4.4/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_remote_execution-1.8.0.4/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_openscap-1.0.8/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_theme_satellite-4.0.1.7/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_bootdisk-15.0.0/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/redhat_access-2.2.8/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.12.0.29/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.12.0.29/engines/bastion/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman-tasks-0.15.11.1/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/foreman_discovery-15.0.2/app/views"
  * "/opt/theforeman/tfm/root/usr/share/gems/gems/apipie-rails-0.5.14/app/views"
):
2019-12-23T12:53:28 [F|app|0525e2ad]   
2019-12-23T12:53:28 [F|app|0525e2ad] app/controllers/application_controller.rb:325:in `generic_exception'
lib/foreman/middleware/telemetry.rb:10:in `call'
lib/foreman/middleware/catch_json_parse_errors.rb:9:in `call'
lib/foreman/middleware/logging_context_session.rb:22:in `call'
lib/foreman/middleware/logging_context_request.rb:11:in `call'
katello (3.12.0.29) lib/katello/prevent_json_parsing.rb:12:in `call'

There are few things to mention here. We can't reliably predict, whether the template will render correctly or not. For obvious errors like syntax errors or missing snippets, that's easy, but for code that is in if-condition, that only gets entered during provisioning, we can't tell. When user provisions the host, we validate the templates by rendering and let user know if the template can't be rendered. But it can change while the host boot obviously. We also can't tell user which line contains the error, because we only know line numbers once ERB tags are compiled. I think line numbers only work if safe mode is disabled.

However I agree we should render different error than 500 if the template rendering fails. Something like 503 would be more appropriate. So, I take it as the request in this BZ. We'll also look if we can improve the message on such error page. At least printing some info with request ID to follow up with person who has access to logs would be good. As stated above, it's not possible to reliably say, what line causes the issue. Last but not least, some errors (not all) may be caught by ERB syntax checker. E.g. unclosed ERB tags. That is also something that can be added.

Created redmine issue https://projects.theforeman.org/issues/29204 from this bug

Hi,
I couldn't reproduce your issue, every time I've got correct error message about the problem.

My steps:
0) Run foreman as "RAILS_ENV=production bundle exec foreman start" (latest develop branch)
1) Created template with "<%= (%>" & GET /unattended/provision?hostname=host.ex.com
Error is displayed: "There was an error rendering the AAA_KICK_PROVISION template: ERF22-6132 [Foreman::Renderer::Errors::SyntaxError]: Syntax error occurred while parsing the template AAA_KICK_PROVISION, make sure you have all ERB tags properly closed and the Ruby syntax is valid. The Ruby error: (string):2 :: parse error on value ";" (tSEMI)"
2) Created template with <%= snippet "non-existent snippet" %> & GET /unattended/provision?hostname=host.ex.com
Error: There was an error rendering the AAA_KICK_PROVISION template: The specified snippet 'non-existent snippet' does not exist, or is not a snippet.

When I checked the application code[1], we are catching StandardError class and returning the error message in response.

Can you please check if you can still reproduce the issue?
Thanks.

[1] https://github.com/theforeman/foreman/blob/f75b27377e82fd9760a67764b64cbc17d66ef3c9/app/controllers/concerns/foreman/controller/template_rendering.rb#L17

I see that in the reproducing steps, the format was "text" but it seems you're reproducing with curl which probably deafults to html. Try GET /unattended/provision?hostname=host.ex.com&format=text (or txt) and you'll see we don't have templates for 500 for plain text format, which masks the original error.

Also the question is, what error code we should use in the case that template contains syntax error. I'd consider 503, the template may be fixed later.

I found the way how to reproduce it, my fault. It wasn't problem with missing format, but with that I was signed in as admin, therefore I've got different behavior. 
So the issue is reproducible and I'm looking into it right now.

Hi,
after some investigation I found that the issue has been fixed in Satellite 6.7 (foreman 1.24), here is the link to PR: https://github.com/theforeman/foreman/pull/6057

Current behavior on Satellite 6.7:

When there is error during rendering template, proper error message is displayed instead of just generic "500 Something went wrong ...".

Examples:

Template with "<%= (%>" will get error:
  There was an error rendering the AAA_KICK_PROVISION template: ERF22-6132 [Foreman::Renderer::Errors::SyntaxError]: Syntax error occurred while parsing the template AAA_KICK_PROVISION, make sure you have all 
  ERB tags properly closed and the Ruby syntax is valid. The Ruby error: (string):2 :: parse error on value ";" (tSEMI)

Template with <%= snippet "non-existent snippet" %> will get error:
  There was an error rendering the AAA_KICK_PROVISION template: The specified snippet 'non-existent snippet' does not exist, or is not a snippet.

Steps to verify:
- Login as admin
- Edit provisioning template, set template to "<%= (%>"
- Go to host detail > Templates > Provisioning template > Review

Correct error message is displayed.

Dylan can you please verify the fix and close the issue if everything is okay?
Thank you

Upon review of our valid but aging backlog the Satellite Team has concluded that this Bugzilla does not meet the criteria for a resolution in the near term, and are planning to close in a month. This message may be a repeat of a previous update and the bug is again being considered to be closed. If you have any concerns about this, please contact your Red Hat Account team.  Thank you.

Thank you for your interest in Red Hat Satellite. We have evaluated this request, and while we recognize that it is a valid request, we do not expect this to be implemented in the product in the foreseeable future. This is due to other priorities for the product, and not a reflection on the request itself. We are therefore closing this out as WONTFIX. If you have any concerns about this feel free to contact your Red Hat Account Team. Thank you.