CDN Caching + Compression Strategy: Cache-Control, TTL, Brotli/Zstd, and Invalidation
CDN Caching + Compression Strategy: Cache-Control, TTL, Brotli/Zstd, and Invalidation
Today, websites heavily rely on Content Delivery Networks (CDNs) to speed up the delivery of pages, lighten the load on servers, and generally enhance the user experience.
Implementing a robust CDN caching strategy along with compression enables websites to serve the content directly from the edge locations rather than the origin server, which results in lower latency and savings on bandwidth. Also, efficient compression leads to reducing the size of files, which makes pages load fast on various devices and network speeds.
Why CDN Caching Strategy Matters
A Content Delivery Network caches static and, in some cases, dynamic content of a website on edge servers that are located in different geographical areas around the globe. When a user tries to access a page, the CDN finds the cached version in the nearest edge location and sends it; thus, it doesn’t need to send every request to the origin server. This method decreases the time delay and makes content delivery faster.
Consequently, websites load faster not only for local users but also for users from remote locations, server infrastructure costs are lower, bandwidth usage is reduced, and server stability is improved during traffic peaks. Also, it facilitates the SEO performance and user engagement overall. In order to reap these benefits, a website should have the right caching configuration, appropriate TTL settings, and effective compression methods.
CDN Caching Strategy
A well-thought-out CDN caching strategy is essentially for deciding which content gets cached, how long it remains in the cache, and the time of its refreshing.
Here is what is usually cached:
- Images
- CSS files
- JavaScript
- Fonts
- Static HTML pages
- API responses (when applicable).
Avoid caching:
- Sensitive user data
- Personalized dashboards
- Authentication responses
- Payment pages
Many CDN providers, such as Amazon CloudFront and Google Cloud CDN, offer the possibility to set caching rules separately.
Cache-Control Header
The cache-control header best practices define how browsers and CDNs store and reuse content.
Important directives:
- max-age: Specifies how long a resource can be cached.
Example
- Cache-Control: public, max-age=31536000
- This tells CDNs and browsers to cache the resource for one year.
- s-maxage: Used specifically for shared caches like CDNs.
Example
- Cache-Control: public, max-age=86400, s-maxage=604800
- Browser caches for one day, but CDN caches for one week.
- immutable: Prevents unnecessary revalidation for versioned assets.
Example:
- Cache-Control: public, max-age=31536000, immutable
- Best used for files like style.v2.css or app.5d3f.js
CloudFront Caching Configuration
CloudFront caching is a feature that is commonly seen in top-scale platforms operating at scale because it is well integrated with the AWS infrastructure and also provides highly flexible caching control.
Performance enhancement can be achieved by setting up caching based on certain headers. But one should be careful not to forward unnecessary headers, which will only hurt cache efficiency. It is best to send only those headers that are absolutely necessary and control their usage through cache policies.
An equally crucial step is to make wise use of cache keys. They should carry only the factors required to determine the cache, such as language, device type, or the necessary query strings. The reason is that adding too many parameters will cause the cache to be fragmented and lower efficiency.
Moreover, edge TTL settings are crucial for performance. CloudFront gives the option to set minimum TTL, default TTL, and maximum TTL, and correctly configuring these values would definitely lead to better cache performance and stability.
Example recommended setup:
Static assets
Default TTL: 1 year
HTML pages
Default TTL: 5 minutes to 1 hour
API responses
TTL: 30 seconds to 5 minutes
Improving Google Cloud CDN Cache Hit Ratio
A high Google Cloud CDN cache hit ratio means most requests are served from the CDN instead of the origin server.
To improve cache hit ratio:
Use Versioned Assets
Instead of updating the same file name, use versioning:
- app.v3.js
- styles.v5.css
This allows long TTL without breaking updates.
Normalize Query Strings
Some query parameters reduce cache efficiency. Remove unnecessary parameters like
- ?utm_source
- ?tracking_id
Enable Compression
Enable compression in order to make files smaller and more efficiently stored at CDN edge locations. This will improve delivery speed and reduce bandwidth usage.
Reduce Cache Fragmentation
Be careful not to stuff with cookies or do device-specific caching unnecessarily, and do not use random query parameters. This hampers caching efficiency and thus the performance of the CDN cache.
Brotli Compression Enable for Faster Delivery
Modern CDNs are equipped to handle sophisticated compression algorithms, and Brotli is among the most efficient ones.
Enabling Brotli compression on your site will boost your website’s performance because it compresses files more efficiently than gzip, which results in smaller file sizes and faster page loading times. This also leads to less bandwidth usage and helps in achieving excellent Core Web Vitals.
Brotli is highly optimized for text-based web assets like HTML, CSS, JavaScript, JSON, and SVG files. Often, Brotli can shrink the file sizes of such assets by around 15% to 25% more than gzip.
Most CDNs take care of applying Brotli compression by default when your site is served over HTTPS, the end user’s browser is capable of using Brotli, and compression settings are correctly configured.
Zstandard Compression for the Web
Zstandard compression web is gaining popularity as a next-generation compression technique for modern websites and applications. Essentially, it is a method of compressing and sending data quickly while maintaining high compression quality.
Zstandard gives you a few key benefits, like faster compression and decompression, good compression ratios, improved server performance and in many instances, reduced CPU usage, because of these advantages, it’s very suitable for scenarios like large API responses, dynamic content, real-time data delivery, and edge computing environments.
In fact, quite a few platforms are experimenting with and embracing Zstandard these days, as it offers a great compromise between speed and compression efficiency compared to older compression methods.
TTL DNS vs CDN
A prevalent misunderstanding is usually DNS TTL vs CDN caching behavior, but in reality, they perform different roles in a website’s operation.
DNS TTL dictates the duration that DNS resolvers keep your domain’s IP address before looking for a new one. So, if the TTL is 300 seconds, the DNS systems will refresh roughly every five minutes. A small DNS TTL is great when you are migrating the infrastructure, moving servers, or changing load balancing, etc., as these kinds of updates can spread quickly.
Meanwhile, CDN TTL dictates the duration of your website content to be cached on CDN edge servers. As an example, a TTL of 86400 seconds means that the content can remain cached for one day. This generally applies to assets like images, scripts, web pages, and API responses.
Simply put, DNS TTL impacts how users reach your servers, while CDN TTL decides how long content is served from a CDN cache rather than the original server.
CDN Cache Invalidation
Setting long TTL values for cache is fine, but there are moments when content has to be refreshed immediately. In this case, CDN cache invalidation plays the most important role. Cache invalidation refers to the process of deleting the stale or outdated files on the CDN so that users get the recent version of the content.
It is pretty much the standard practice in a number of situations, such as a web redesign, security patches, fixing content errors, updating prices, or changing products. Once the old cache has been cleared, the CDN rapidly begins serving the updated files to the users. Here are some methods of invalidation:
Path-based Invalidation
Path based invalidation is a technique that helps to get rid of one or more files that are cached on CDN instead of wiping out the whole cache. Such a method is not only more efficient but also lessens the burden of the origin server. You may, for instance, invalidate a folder like
/images/
to essentially refresh all the images or a particular file such as
/css/main.css
When it has been changed. In this way, the new content is delivered to the user without any impact on other cached items.
Full Cache Purge
This method wipes the whole CDN cache by completely deleting all cached content. It must be handled with caution, as it could result in a sudden spike in traffic to the origin server since new requests will have to retrieve fresh content again.
Versioned Deployment (Best Practice)
There are many teams that choose to release new versioned assets like.
- app.v6.js
- style.v8.css
This approach ensures users receive updated files immediately, prevents cache conflicts, and improves reliability while allowing long cache durations for static content.
This method ensures that users get the updated files right away, thus it helps to avoid cache conflicts and makes the system more reliable. At the same time, it allows very long caching periods for content that doesn’t change.
Recommended CDN Optimization Architecture
A robust caching and compression arrangement typically comprises the following:
Layer 1: Browser Cache
- Cache-Control headers
- Long TTL for static asset
Layer 2: CDN Edge Cache
- Optimized cache keys
- Query normalization
- Brotli compression
- Aggressive caching
Layer 3: Origin Shield
- Reduces load on backend servers
- Prevents traffic spikes
Layer 4: Compression Pipeline
- Brotli for browsers
- Zstandard for backend or edge processing
Performance Impact of a Well-Configured CDN Strategy
Organizations implementing a thoroughly thought-out CDN setup can expect surprising results regarding website performance and efficiency. Oftentimes, users’ waiting times for loading web pages are shortened by 40% to 70% when content is served locally by the nearest edge servers instead of being fetched from the origin server.
Also, requests that still go through the origin server may reduce by 60% to 90%, which greatly lightens the burden on your servers types. Besides, such a solution can cut down on bandwidth usage and thus be a stabilizing factor during times of increased traffic when the website is being accessed by a large number of users simultaneously.
Eventually, as more requests are handled directly from the CDN cache, the cache hit ratio goes up, thereby being instrumental in diminishing the cost of infrastructure over time and guaranteeing users a smooth experience consistently.
Conclusion
A modern CDN setup goes beyond simple caching. It involves a carefully planned mix of the following best practices for cache-control headers, using smart TTL settings, applying efficient compression techniques such as enabling Brotli compression and web Zstandard compression, and having a dependable CDN cache invalidation process.
Using a well-thought CDN caching strategy, a website can expand its reach worldwide, lower its infrastructure expenses, and provide the same user experience across all locations. In case you are tuning CloudFront caching or working on your Google Cloud CDN cache hit ratio, the proper setting can make a remarkable difference in the site speed and the level of its reliability.
FAQs
What is CDN caching?
CDN caching involves storing content on edge servers so that content can be served from a nearby server. This not only saves time but also reduces the load on the main server and network traffic.
What is Cache-Control?
Cache-Control is a header used to specify the caching strategy. For example, it tells how long browsers or CDNs are allowed to cache certain content.
How does Brotli compression help?
Brotli compression compresses the size of files. The smaller the files, the faster the pages get loaded, and in addition, there will be less use of data, which in turn improves SEO.
What is TTL in CDN?
TTL (Time to Live) is a parameter that states the duration for which content in the CDN edge servers remains valid in cache before the content gets refreshed or expires.
Why is cache invalidation important?
Cache invalidation confirms that the CDN does not contain old content, so users get updated content straight away.