In recent years, more and more platforms for optimizing front-end projects offer the possibility of self-hosting or proxying third-party resources. Akamai allows you to set for self-generated URLs. Cloudflare has Edge Workers technology. Fasterzine can URLs on pages so that they point to third-party resources located on the main domain of the site.
If you know that third-party services used in your project do not change too often, and that the process of delivering them to clients can be improved, then you are probably thinking about proxying such services. With this approach, you can very well "bring" these resources closer to users and gain more control over their caching on the client side. This, moreover, allows you to protect users from troubles caused by the "fall" of a third-party service or the degradation of its performance.
Good: performance improvement
Self-hosting other people's resources improves performance in a very obvious way. The browser doesn't need to look up DNS again, it doesn't need to establish a TCP connection and perform a TLS handshake on a third-party domain. How self-hosting someone else's resources affects performance can be seen by comparing the following two figures.
Third-party resources are loaded from external sources (taken )
Third-party resources are stored in the same place as the rest of the site materials (taken )
The situation is further improved by the fact that the browser will use the data multiplexing and prioritization capabilities of the HTTP/2 connection that is already established with the main domain.
If you do not host third-party resources, then since they will be loaded from a domain other than the main one, they cannot be prioritized. This will cause them to compete with each other for client bandwidth. This can result in loading times that are critical for page generation to be much longer than what would be achievable under ideal circumstances. a talk on HTTP/2 prioritization that explains it all very well.
It can be assumed that the use of attributes in links to external resources preconnect will help in solving the problem. However, if there are too many such links to different domains, it can, in fact, overload the communication line at the most crucial moment.
If you host third-party resources yourself, you can control exactly how these resources are given to the client. Namely, we are talking about the following:
- It is possible to ensure that the data compression algorithm best suited for each browser (Brotli/gzip) is used.
- You can increase the caching time for resources that are usually not particularly long even with the most well-known providers (for example, the corresponding value for the GA tag is set to 30 minutes).
You can even extend the TTL of a resource to, say, a year by including the appropriate content in your caching management strategy (URL hashes, versioning, and so on). We will talk about this below.
βProtection against interruptions in the operation of third-party services or their shutdown
Another interesting aspect of self-hosting third-party resources is that it allows you to mitigate the risks associated with outages of third-party services. Let's assume that the third-party A/B testing solution you're using is implemented as a blocking script loaded in the header section of the page. This script loads slowly. If the corresponding script fails to load, the page will also be empty. If it takes a very long time to load, the page will appear with a long delay. Or, suppose the project uses a library loaded from a third-party CDN resource. Let's imagine that this resource experienced a failure or was blocked in a certain country. This situation will lead to a violation of the logic of the site.
In order to find out how your site works when some external service is unavailable, you can use the SPOF section on .
SPOF section on webpagetest.org
βWhat about browser caching issues? (hint: it's a myth)
You might think that using public CDNs will automatically lead to better resource performance, since these services have fairly good networks and are distributed all over the world. But it's actually a little more complicated.
Suppose we have several different sites: website1.com, website2.com, website3.com. All of these sites use the jQuery library. We connect it to them using a CDN, for example, googleapis.com. You can expect the browser to download and cache the library once, and then use it when working with all three sites. This could reduce the load on the network. Perhaps this will save somewhere and help improve the performance of resources. From a practical point of view, things look different. For example, Safari has a feature called : The cache uses dual keys based on the origin of the document and the origin of the third party resource. good article on this topic.
old studies ΠΈ , as well as fresher Paul Calvano, show that resources are not stored in browser caches for as long as we might expect: βThere is a serious gap between the caching time of a project's own and third-party resources. It's about CSS and web fonts. Namely, 95% of native fonts cache for over a week, while 50% of third-party fonts cache for less than a week! This gives web developers a good reason to self-host font files!β.
As a result, if you host other people's content, you won't notice performance issues caused by browser caching.
Now that we've covered the strengths of self-hosting third-party resources, let's talk about how to tell a good implementation of this approach from a bad one.
Bad: The devil is in the details
Moving third-party resources to your own domain cannot be done automatically without taking care of proper caching of such resources.
One of the main issues here is caching time. For example, versioning information is included in third-party script names like this: jquery-3.4.1.js. Such a file will not change in the future, as a result it will not cause any problems with its caching.
But if some versioning scheme is not used when working with files, cached scripts whose contents change while the file name remains unchanged can become outdated. This can become a serious problem, as it, for example, does not allow you to automatically apply security patches to scripts that customers should receive as soon as possible. The developer will have to make an effort to update such scripts in the cache. In addition, it can cause application crashes due to the fact that the code used on the client from the cache differs from the latest version of the code that the backend of the project was designed for.
True, if we talk about materials that are updated frequently (tag managers, solutions for A / B testing), then their caching using CDN tools is a task that, although solvable, is already much more complicated. Services like Commanders Act, a tag management solution, use webhooks when publishing new versions. This makes it possible to organize a cache flush on the CDN, or, even better, the ability to call a hash update or URL version update.
βAdaptive delivery of materials to customers
In addition, when we talk about caching, we need to take into account the fact that the caching settings used on the CDN may not be suitable for some third-party resources. For example, such resources may use user agent sniffing (adaptive serving) to serve browser-specific versions of content that are optimized specifically for those browsers. These technologies rely on regular expressions, or a database that collects information about the HTTP header, to figure out the capabilities of the browser. User-Agent. When they find out what browser they are dealing with, they give it materials designed for it.
There are two services here. The first is googlefonts.com. The second is polyfill.io. The Google Fonts service provides, for a certain resource, a different CSS code depending on the capabilities of the browser (giving links to woff2 resources using unicode-range).
Here are the results of a couple of requests to Google Fonts made from different browsers.
Google Fonts query result from Chrome
Google Fonts query result made from IE10
Polyfill.io gives the browser only the polyfills it needs. This is done for performance reasons.
For example, let's take a look at what happens if we run the following request from different browsers:
In response to such a request, executed from IE10, 34 KB of data will come. And the answer to it, executed from Chrome, will be empty.
Evil: some privacy considerations
This item is last but not least. We are talking about the fact that self-hosting of third-party resources on the main project domain or on its subdomain can jeopardize the privacy of users and adversely affect the main web project.
If your CDN system is set up incorrectly, you may end up sending your domain cookies to a third party service. If proper filtering is not organized at the CDN level, then your session cookies, which cannot normally be used in JavaScript (with the attribute httponly) can be sent to a foreign host.
This is exactly what can happen with trackers like Eulerian or Criteo. Third party trackers may have set a unique identifier in cookies. They, if they were part of the materials of the sites, could read the identifier at their own discretion during the user's work with different web resources.
Most browsers these days include protection against this kind of tracker behavior. As a result, trackers now use technology , masquerading as their own scripts of various projects. Namely, trackers offer site owners to add to their settings a CNAME for a certain domain, the address of which usually looks like a random set of characters.
While it's not recommended to make website cookies available to all subdomains (eg *.website.com), many sites do. In such a case, such cookies are automatically sent to a disguised third-party tracker. As a result, you can no longer talk about any privacy.
Also, the same thing happens with HTTP headers , which are sent only to the main domain, since they can be used to create user. Please make sure that the CDN service you are using correctly filters these headers.
Results
If you are going to implement self-hosted third-party resources soon, let me give you some tips:
- Host your most important JS libraries, fonts and CSS files. This will reduce the risk of site failure or performance degradation due to the fact that a resource vital for the operation of the site is unavailable due to the fault of a third-party service.
- Before caching third-party resources on the CDN, make sure that their file names use some versioning system, or that you can control the lifecycle of these resources by manually or automatically flushing the CDN cache when publishing a new version of the script.
- Be very careful about the settings of the CDN, proxy server, cache. This will allow you to prevent your project's cookies or headers from being sent.
Client-Hintsthird party services.
Dear Readers, Do you host other people's materials on your servers that are extremely important for the operation of your projects?
Source: habr.com