Cache render_for_web field for alertgroups list serializer (#1236)

# What this PR does
This PR caches the field `render_for_web` with lifetime 1 day and cache
becomes invalid if it was created before
* last alert received
* template changed


## Which issue(s) this PR fixes

## Checklist

- [ ] Tests updated
- [ ] Documentation added
- [ ] `CHANGELOG.md` updated

engine/apps/alerts/migrations/0009_alertreceivechannel_web_templates_modified_at.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.16 on 2023-01-27 07:41
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('alerts', '0008_alter_alertgrouplogrecord_type'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='alertreceivechannel',
+            name='web_templates_modified_at',
+            field=models.DateTimeField(blank=True, null=True),
+        ),
+    ]

engine/apps/alerts/models/alert_receive_channel.py

@@ -160,6 +160,7 @@ class AlertReceiveChannel(IntegrationOptionsMixin, MaintainableObject):
     web_title_template = models.TextField(null=True, default=None)
     web_message_template = models.TextField(null=True, default=None)
     web_image_url_template = models.TextField(null=True, default=None)
+    web_templates_modified_at = models.DateTimeField(blank=True, null=True)
 
     # email related fields are deprecated in favour of messaging backend based templates
     # these templates are stored in the messaging_backends_templates field

engine/apps/api/serializers/alert_group.py

@@ -1,5 +1,7 @@
 import logging
 
+from django.core.cache import cache
+from django.utils import timezone
 from rest_framework import serializers
 
 from apps.alerts.incident_appearance.renderers.classic_markdown_renderer import AlertGroupClassicMarkdownRenderer
@@ -13,6 +15,7 @@ from .alert_receive_channel import FastAlertReceiveChannelSerializer
 from .user import FastUserSerializer
 
 logger = logging.getLogger(__name__)
+logger.setLevel(logging.DEBUG)
 
 
 class ShortAlertGroupSerializer(serializers.ModelSerializer):
@@ -92,10 +95,33 @@ class AlertGroupListSerializer(EagerLoadingMixin, serializers.ModelSerializer):
         if not obj.last_alert:
             return {}
 
-        return AlertGroupWebRenderer(obj, obj.last_alert).render()
+        web_templates_modified_at = obj.channel.web_templates_modified_at
+        last_alert_created_at = obj.last_alert.created_at
+
+        CACHE_KEY = f"render_for_web_alert_group_{obj.id}"
+        CACHE_LIFEIME = 60 * 60 * 24
+        cached_render_for_web = cache.get(CACHE_KEY, None)
+
+        # use cache only if cache exists
+        # and cache was created after the last alert created
+        # and either web templates never modified
+        # or cache was created after templates were modified
+        if (
+            cached_render_for_web is not None
+            and cached_render_for_web.get("cache_created_at") > last_alert_created_at
+            and (
+                web_templates_modified_at is None
+                or cached_render_for_web.get("cache_created_at") > web_templates_modified_at
+            )
+        ):
+            render_for_web = cached_render_for_web.get("render_for_web")
+        else:
+            render_for_web = AlertGroupWebRenderer(obj, obj.last_alert).render()
+            cache.set(CACHE_KEY, {"cache_created_at": timezone.now(), "render_for_web": render_for_web}, CACHE_LIFEIME)
+
+        return render_for_web
 
     def get_render_for_classic_markdown(self, obj):
-        # alert group has no alerts
         if not obj.last_alert:
             return {}
 

engine/apps/api/serializers/alert_receive_channel.py

@@ -7,6 +7,7 @@ from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError as DjangoValidationError
 from django.core.validators import URLValidator
 from django.template.loader import render_to_string
+from django.utils import timezone
 from jinja2 import TemplateSyntaxError
 from rest_framework import serializers
 from rest_framework.exceptions import ValidationError
@@ -379,6 +380,7 @@ class AlertReceiveChannelTemplatesSerializer(EagerLoadingMixin, serializers.Mode
             self.instance.web_title_template = value.strip()
         elif default_template is not None and default_template.strip() == value.strip():
             self.instance.web_title_template = None
+        self.instance.web_templates_modified_at = timezone.now()
 
     def get_web_message_template(self, obj):
         default_template = AlertReceiveChannel.INTEGRATION_TO_DEFAULT_WEB_MESSAGE_TEMPLATE[obj.integration]
@@ -390,6 +392,7 @@ class AlertReceiveChannelTemplatesSerializer(EagerLoadingMixin, serializers.Mode
             self.instance.web_message_template = value.strip()
         elif default_template is not None and default_template.strip() == value.strip():
             self.instance.web_message_template = None
+        self.instance.web_templates_modified_at = timezone.now()
 
     def get_web_image_url_template(self, obj):
         default_template = AlertReceiveChannel.INTEGRATION_TO_DEFAULT_WEB_IMAGE_URL_TEMPLATE[obj.integration]
@@ -401,6 +404,7 @@ class AlertReceiveChannelTemplatesSerializer(EagerLoadingMixin, serializers.Mode
             self.instance.web_image_url_template = value.strip()
         elif default_template is not None and default_template.strip() == value.strip():
             self.instance.web_image_url_template = None
+        self.instance.web_templates_modified_at = timezone.now()
 
     def get_telegram_title_template(self, obj):
         default_template = AlertReceiveChannel.INTEGRATION_TO_DEFAULT_TELEGRAM_TITLE_TEMPLATE[obj.integration]