Instrument Twirl template with a java agent

[alexduf]

See #28909 and #28894

This was coded with the help of Opus 4.8. I don't think I could have cooked it this quick otherwise.

What is the value of this and can you measure success?

Can we measure which twirl template is being used in production? if so: success.

What does this change?

Instrument production artefacts at runtime in order to detect which twirl templates truly are used in a live environment. The instrumentation writes a json log line in a separate file each time a new template is encountered.

The logging implementation is voluntarily naive, it's inefficient but it's a trade-off for simplicity that I'm willing to accept because:

• the number of log lines is going to be very small (< 200)
• it will only be slowing down the first few requests
• keeping this code as simple as technically feasible is key for maintainability

As of now this is only applied to the discussion service, and it will be generalised in this ticket

Screenshots

root@ip-10-0-1-41:/home/discussion/logs# tail -n10000 -f twirl-usage.log
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.discussionComments.discussionPage", "timestamp":"2026-07-03T08:57:23.164191162Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.comment", "timestamp":"2026-07-03T08:57:23.280691371Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.inlineSvg", "timestamp":"2026-07-03T08:57:23.317208482Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.commentBadges", "timestamp":"2026-07-03T08:57:23.451675149Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.commentPagination", "timestamp":"2026-07-03T08:57:23.808396215Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.pagination", "timestamp":"2026-07-03T08:57:23.83499089Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.reportComment", "timestamp":"2026-07-03T08:57:23.856467665Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.recommendationTooltip", "timestamp":"2026-07-03T08:57:23.872501405Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.mainLegacy", "timestamp":"2026-07-03T08:57:23.876149815Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.main", "timestamp":"2026-07-03T08:57:23.900311874Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.head", "timestamp":"2026-07-03T08:57:23.926315961Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.metaData", "timestamp":"2026-07-03T08:57:23.972617671Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.stylesheets", "timestamp":"2026-07-03T08:57:24.207628616Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.fontFaces", "timestamp":"2026-07-03T08:57:24.22786444Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.stylesheetLink", "timestamp":"2026-07-03T08:57:24.249071521Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.page.head.fixIEReferenceErrors", "timestamp":"2026-07-03T08:57:24.283257482Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.page.head.checkModuleSupport", "timestamp":"2026-07-03T08:57:24.299675049Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.inlineJSBlocking", "timestamp":"2026-07-03T08:57:24.32102723Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.commercial.topBanner", "timestamp":"2026-07-03T08:57:25.785808864Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.commercial.standardAd", "timestamp":"2026-07-03T08:57:25.81496349Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.commercial.adSlot", "timestamp":"2026-07-03T08:57:25.853580442Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.header", "timestamp":"2026-07-03T08:57:25.872392544Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.nav.userAccountDropdown", "timestamp":"2026-07-03T08:57:25.925532721Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.nav.editionPickerDropdown", "timestamp":"2026-07-03T08:57:25.953651679Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.nav.headerMenu", "timestamp":"2026-07-03T08:57:25.970834776Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.nav.editionPicker", "timestamp":"2026-07-03T08:57:26.052853344Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.nav.subNav", "timestamp":"2026-07-03T08:57:26.084050579Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.footer", "timestamp":"2026-07-03T08:57:26.11388966Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.email.signup.emailFooterLink", "timestamp":"2026-07-03T08:57:26.14095677Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.message", "timestamp":"2026-07-03T08:57:26.196277385Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.inlineJSNonBlocking", "timestamp":"2026-07-03T08:57:26.215546915Z[Etc/UTC]"}
{"marker":"TEMPLATE_FIRST_SEEN","template":"views.html.fragments.analytics.base", "timestamp":"2026-07-03T08:57:26.361353019Z[Etc/UTC]"}

Checklist

• Tested locally, and on CODE if necessary
• Will not break dotcom-rendering
• Any new test data/database files generated by tests are committed with this PR (the tests will fail in CI if you've forgotten to do this)
• Meets our accessibility standards
  • Tested with screen reader
  • Navigable with keyboard
  • Colour contrast passed

[github-actions]

Deploy build 7268 of dotcom:frontend-all to CODE

All deployment options

• Deploy build 7268 of dotcom:frontend-all to CODE
• Deploy parts of build 7268 to CODE by previewing it first
• What's on CODE right now?

---

From guardian/actions-riff-raff.

[alexduf]

I've also tested adding a "decoy" twirl template hidden behind an impossible condition (1+1 == 3) just to ensure that its name would not appear in the list (which would mean appearing simply for being referenced rather than executed). The test is conclusive.

[gu-prout]

Seen on ADMIN-PROD (merged by @alexduf 9 minutes and 10 seconds ago)

• Check your changes on www.theguardian.com ✔️
• Keep an eye on the deploy dashboard 📉

[gu-prout]

Seen on FRONTS-PROD (merged by @alexduf 9 minutes and 17 seconds ago)

• Check your changes on www.theguardian.com ✔️
• Keep an eye on the deploy dashboard 📉