Added varnish hitrate docs

Author: TimVNL

docs/hypernode-platform/tools/improving-varnish-cache-hit-rate.md

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+---
+myst:
+  html_meta:
+    description:  Learn how to improve your Varnish cache hit rate on Hypernode by identifying automatic cache purges, analyzing hit/miss patterns, and optimizing URL normalization to boost performance and efficiency.
+    title: Improving Varnish Cache Hit Rate on Hypernode
+---
+
+# Improving Your Varnish Cache Hit Rate
+
+A higher Varnish cache hit rate means more pages are served directly from cache.
+This reduces backend resource usage on your Hypernode, improves page load speed, and helps your shop handle more concurrent visitors without performance degradation.
+
+A low hit rate often indicates that cache isn’t being reused effectively, typically caused by misconfiguration, frequent invalidation, or too much variation in URLs.
+
+This guide takes you step-by-step from verifying that your cache is active to diagnosing and improving your hit ratio.
+
+## Before You Begin
+
+Typical cache hit rates:
+- **Below 10%** → Cache is barely reused  
+- **30–70%** → Improvement possible (depends on shop type)  
+- **Above 80%** → Generally healthy  
+
+Keep in mind:
+- Staging environments typically have low hit rates  
+- B2B webshops often have lower hit rates due to personalization  
+
+
+# Step 1 — Verify Varnish Is Enabled
+
+Ensure Varnish is properly enabled on your Hypernode and configured in your
+application (e.g. Magento 2).
+
+For Magento 2, verify:
+- Varnish is selected as the caching application
+- The correct VCL is generated and loaded
+- Full Page Cache (FPC) is enabled
+
+For a complete guide on how to configure Varnish in Magento 2 see: 
+https://docs.hypernode.com/ecommerce-applications/magento-2/how-to-configure-varnish-for-magento-2-x.html#how-to-configure-varnish-for-magento-2-x
+
+```{tip}
+Tip: The [elgentos/magento2-varnish-extended](https://github.com/elgentos/magento2-varnish-extended) extension improves Magento’s
+default VCL configuration and marketing parameter handling.
+```
+
+# Step 2 — Check if Pages Are Being Cached
+
+Use `curl` to inspect response headers:
+
+```console
+curl -I https://yourdomain.com
+```
+
+Look for:
+- `X-Cache: HIT` → Served from Varnish
+- `X-Cache: MISS` → Served from backend
+- `Age` → How long the object has been cached
+- `X-Magento-*` headers → Useful Magento cache debug info only visible when developer mode is enabled.
+
+If most responses return `MISS`, caching is not being reused effectively.
+
+You can also inspect these headers in your browser via:
+Developer Tools → Network tab → Select request → Response Headers
+
+---
+
+# Step 3 — Measure Your Cache Hit Rate
+
+Run:
+
+```console
+varnishstat -1 -f MAIN.cache_hit -f MAIN.cache_miss
+```
+
+This shows:
+- `MAIN.cache_hit` → Cached responses served
+- `MAIN.cache_miss` → Requests sent to backend
+
+A high miss count relative to hits indicates room for improvement.
+
+For live monitoring:
+
+```console
+varnishstat
+```
+
+---
+
+# Step 4 — Common Causes of Low Hit Rates
+
+## 1. Pages Bypassing Varnish
+
+Some pages are intentionally not cached:
+- Checkout
+- Customer account pages
+- Requests containing `Set-Cookie` headers
+
+This is expected behavior.
+
+## 2. Frequent Cache Invalidations
+
+If cache clears happen frequently, reuse becomes impossible.
+
+Common causes:
+- Stock or pricing integrations
+- Magento cron jobs performing full cache purges
+- Extensions invalidating excessive cache entries
+
+Best practice:
+Perform targeted purges (specific URLs or cache tags) instead of full cache
+flushes.
+
+---
+
+## 3. Marketing & Tracking Parameters
+
+Tracking parameters create separate cache entries for identical content.
+
+Examples:
+- `utm_source`
+- `utm_medium`
+- `gclid`
+- `fbclid`
+
+Example problem:
+- /product-x
+- /product-x?utm_source=google
+
+These generate separate cache objects unless normalized.
+
+Solution:
+
+Strip non-essential tracking parameters in VCL.
+
+```{tip}
+The [elgentos/magento2-varnish-extended](https://github.com/elgentos/magento2-varnish-extended) module improves this behavior.
+```
+---
+
+## 4. URL Normalization Issues
+
+Different URL formats fragment your cache.
+
+Examples:
+- `/category` vs `/category/`
+- `?Color=Red` vs `?color=red`
+- Unsorted query parameters
+- Session IDs in URLs
+
+Normalize URLs to ensure identical content maps to a single cache object.
+
+---
+
+## 5. Non-Cacheable Magento Blocks
+
+In Magento, a single block marked as non-cacheable can disable Full Page Cache
+for the entire page.
+
+Search for non-cacheable blocks:
+
+```console
+grep -R "cacheable=\"false\"" app/code vendor
+```
+If found:
+- Verify the block truly needs to be dynamic
+- Remove cacheable="false" if unnecessary
+- Use AJAX or Customer Data Sections for dynamic content
+
+Even one unnecessary non-cacheable block can severely impact hit rate.
+
+# Optional — Enable Magento Developer Mode for Debugging
+
+Developer mode provides more detailed error output:
+```console
+magerun2 deploy:mode:set developer
+```
+
+Or: 
+```console
+php bin/magento deploy:mode:set developer
+```
+
+# Debugging Tools
+
+## varnishlog
+Inspect detailed request handling:
+```bash
+varnishlog
+```
+Look for recurring MISS patterns on pages that should be cacheable.
+
+## varnishncsa
+Show hit/miss per URL:
+```bash
+varnishncsa -F '%U%q %{Varnish:hitmiss}x'
+```
+Filter for hits:
+```bash
+varnishncsa -F '%U%q %{Varnish:hitmiss}x' | grep hit
+```
+
+## Hypernode Insights (If Available)
+Use Hypernode Insights to:
+- Monitor hit/miss ratios
+- Detect purge spikes
+- Correlate cache drops with deployments or cron jobs