How to debug "ERROR in SERVER PRERENDERING" when there is no output

[JaredShay]

I've recently added react_on_rails to an application and am slowly rolling out SSR components. There have been two errors with the following:

ActionView::Template::Error: ERROR in SERVER PRERENDERING
Encountered error:

Error evaluating server bundle. Check your webpack configuration.
===============================================================
Caught error:

================================

when prerendering ProMarketingCTAs with props: {"shouldOverlapPaywall":true}

code:

        (function() {
          var railsContext = {"railsEnv":"production","inMailer":false,"i18nLocale":"en","i18nDefaultLocale":"en","rorVersion":"13.3.4","rorPro":false,"href":"https://www.theinformation.com/org-charts/snap","location":"/org-charts/snap","scheme":"https","host":"www.theinformation.com","port":null,"pathname":"/org-charts/snap","search":null,"httpAcceptLanguage":null,"serverSide":true};
              ReactOnRails.clearHydratedStores();

          var props = {"shouldOverlapPaywall":true};
          return ReactOnRails.serverRenderReactComponent({
            name: 'ProMarketingCTAs',
            domNodeId: 'ProMarketingCTAs-react-component-9524e97b-5d8d-4ee6-9e10-4c744f528be9',
            props: props,
            trace: false,
            railsContext: railsContext
          });
        })()

The Caught error: is showing the output from a call within the execjs gem:

def exec_runtime(filename)
  io = IO.popen(binary.split(' ') << filename, **(@popen_options.merge({err: [:child, :out]})))
  output = io.read
  io.close

  if $?.success?
    output
  else
    raise exec_runtime_error(output) # this is the line that is raising, output is `nil` or `''`
  end
end

And the component and function referenced appear to work correctly. The page where this error has occurred appears to work. It is from a reasonably high traffic site and this error report appears to be very intermittent and rare.

I can't reproduce this so I can't file a bug report. Does anyone have suggestions for what to do to debug this further? My main concern is if I scale up the usage of SSR I'm not sure how to diagnose issues when I'm getting no output.

[justin808]

@JaredShay you have an issue in your webpack configuration to build a server bundle.

You might post to our community Slack

If you'd like ShakaCode to help you out so that you can focus on new features as opposed to configuring Webpack, please book a time with me or email me: justin@shakacode.com.

[Judahmeek]

@JaredShay try ensuring that you're using NodeJS for your EXECJS_RUNTIME.

MiniRacer isn't compatible with certain libraries & javascript features.

Additionally, there's a possibility that this is being caused by a new webserver worker getting a SSR request before the server-bundle has been compiled.

At least, I think that's an edge case we've encountered before. I'm having trouble tracking down any details on it, however.