cache queries and revalidate with incremental static regeneration

dnscms/dnscms/apps.py

@@ -6,3 +6,6 @@ class DnsCmsConfig(AppConfig):
 
     def ready(self):
         from dnscms import signals  # noqa: F401
+        from dnscms.revalidation import register_signal_handlers
+
+        register_signal_handlers()

dnscms/dnscms/revalidation.py

@@ -0,0 +1,97 @@
+"""Purge the frontend cache when content changes.
+
+The frontend caches all GraphQL responses under a single "cms" cache tag;
+any content change POSTs to its /api/revalidate endpoint for a global purge.
+"""
+
+import logging
+import threading
+import urllib.request
+
+from django.conf import settings
+from django.db import transaction
+from django.db.models.signals import post_delete, post_save
+
+logger = logging.getLogger(__name__)
+
+WEBHOOK_TIMEOUT_SECONDS = 5
+
+# Non-page models exposed over GraphQL; pages are covered by wagtail signals
+REVALIDATING_MODELS = [
+    "contacts.ContactEntity",
+    "events.EventCategory",
+    "events.EventOrganizer",
+    "images.CustomImage",
+    "openinghours.OpeningHoursSet",
+]
+
+_warned_unconfigured = False
+
+
+def _send_webhook(url, secret, reason):
+    request = urllib.request.Request(
+        url, data=b"", method="POST", headers={"X-Revalidate-Secret": secret}
+    )
+    try:
+        with urllib.request.urlopen(request, timeout=WEBHOOK_TIMEOUT_SECONDS) as response:
+            logger.info("frontend revalidation ok (%s): HTTP %s", reason, response.status)
+    except Exception:
+        logger.exception("frontend revalidation failed (%s)", reason)
+
+
+def trigger_frontend_revalidation(reason):
+    global _warned_unconfigured
+    secret = settings.REVALIDATE_WEBHOOK_SECRET
+    if not secret:
+        if not _warned_unconfigured:
+            logger.warning("REVALIDATE_WEBHOOK_SECRET is not set, skipping frontend revalidation")
+            _warned_unconfigured = True
+        return
+    url = f"{settings.FRONTEND_BASE_URL}/api/revalidate"
+    # After commit so the frontend can't re-render from pre-commit data,
+    # in a thread so publishing never blocks on the frontend
+    transaction.on_commit(
+        lambda: threading.Thread(
+            target=_send_webhook, args=(url, secret, reason), daemon=True
+        ).start()
+    )
+
+
+def _on_page_published(sender, instance, **kwargs):
+    trigger_frontend_revalidation(f"page_published: {instance.slug}")
+
+
+def _on_page_unpublished(sender, instance, **kwargs):
+    trigger_frontend_revalidation(f"page_unpublished: {instance.slug}")
+
+
+def _on_page_moved(sender, instance, **kwargs):
+    trigger_frontend_revalidation(f"post_page_move: {instance.slug}")
+
+
+def _on_page_deleted(sender, instance, **kwargs):
+    trigger_frontend_revalidation(f"page_deleted: {instance.slug}")
+
+
+def _on_model_changed(sender, instance, **kwargs):
+    trigger_frontend_revalidation(f"{sender._meta.label}: {instance}")
+
+
+def register_signal_handlers():
+    from wagtail.models import Page
+    from wagtail.signals import page_published, page_unpublished, post_page_move
+
+    page_published.connect(_on_page_published, dispatch_uid="revalidation.page_published")
+    page_unpublished.connect(_on_page_unpublished, dispatch_uid="revalidation.page_unpublished")
+    post_page_move.connect(_on_page_moved, dispatch_uid="revalidation.post_page_move")
+    # Wagtail sends no signal on page deletion; MTI deletes of any page type
+    # also emit post_delete for the base Page row
+    post_delete.connect(_on_page_deleted, sender=Page, dispatch_uid="revalidation.page_deleted")
+
+    for label in REVALIDATING_MODELS:
+        post_save.connect(
+            _on_model_changed, sender=label, dispatch_uid=f"revalidation.save.{label}"
+        )
+        post_delete.connect(
+            _on_model_changed, sender=label, dispatch_uid=f"revalidation.delete.{label}"
+        )

dnscms/dnscms/settings/base.py

@@ -200,6 +200,10 @@ BASE_URL = WAGTAIL_BASE_URL
 # redirect "View Live" clicks on the CMS host over to the headless frontend.
 FRONTEND_BASE_URL = os.environ.get("FRONTEND_BASE_URL", "http://localhost:3000").rstrip("/")
 
+# Shared secret for the frontend cache purge webhook (see dnscms/revalidation.py).
+# Unset means no webhooks are sent.
+REVALIDATE_WEBHOOK_SECRET = os.environ.get("REVALIDATE_WEBHOOK_SECRET", "")
+
 WAGTAIL_HEADLESS_PREVIEW = {
     "CLIENT_URLS": {"default": f"{FRONTEND_BASE_URL}/api/preview"},
     "SERVE_BASE_URL": FRONTEND_BASE_URL,