Generally, we don’t have stability issues.

Bottlenecks exist only at the highest levels. The standard version of Drupal is slightly more demanding than the other baseline platforms, with a hunger for >512MB of memory for rendering heavier scripts.

The solution is very scalable. We like it.

I never thought that there was anything that we couldn't do with Drupal.

Drupal 8 has an architecture that will scale well and better than previous versions, especially given big pipe. This will allow for scaling, even with authenticated users. This is something that was not possible in earlier versions.

When we built an application reaching 200k unique hits, we were suffering from severe slowness. We had to change our approach to caching and the use of a load-balanced setup.

We made a load-balanced setup consisting of four nodes and added a Varnish and Memcache dedicated instance per node.

This allowed us to have a response time of less than a second, even with 200k unique hits per hour.

I did not encounter any issues with scalability.

I did not encounter any scalability issues. The scalability/modularity is one of the principle features of this CMS.

Drupal, especially the recent versions, is built to easily integrate with systems like Varnish. Scalability is not an issue, provided that you know how to use this kind of setup.

Drupal 8 goes further. It uses a new cache system which allows integration with a lot of existing performance techniques:

• BigPipe from Facebook (https://www.facebook.com/notes...-engineering/bigpipe-pipelining-web-pages-for-high-performance/389414033919/): Now bundled into the Drupal core
• Turbolinks from Ruby on Rails (https://github.com/turbolinks/turbolinks): Can be integrated using a community module

There have been no scalability issues.

Scalability is something that can be related to many factors, depending on your needs and the budget you have. It is also related to the way you architect your solution and therefore how you implement your Drupal website. A bad architecture, in terms of content, can drastically reduce it.

Drupal Version 8 is based on a typical PHP + MySQL/MariaDB + Apache/NGiNX stack. These have been in the market for some time. They are hosting providers who are selling Drupal cloud services with promises of scalability.

There were no scalability issues. This product can be scaled as much as you want.

Verbatim from Drupal.org (https://www.drupal.org/docs/7/managing-site-performance-and-scalability):

Drupal is a complex application. A well-configured Drupal site can be highly performant and can scale to many millions of visitors per day. Conversely, a poorly optimized site can be frustratingly slow for its users.

In our project, we've followed guidelines from drupal.org as to how to optimize its performance for scalability. It has helped us to serve our site from tens to thousands of regular users.

Drupal may require a lot of resources for certain types of sites, but hosting and well-architected codes can get around this.

So far, Drupal 8 has been doing an excellent job with all the integrations that it provides. So the answer is, so far, there were no scalability issues.

If custom development follows the best practices and standards, it shouldn’t be any problem. However, when custom parts don’t follow the standards, there could be room for scalability problems.

Scalability is one of the key factors that make Drupal so widely accepted.

The wide number of implementation options will often cause developers without a lot of Drupal experience to paint themselves into a corner.

Being one of the strong points of Drupal, I would not say I had issues with scalability! The learning curve might be a bit longer in the new version, since it has converted to OOP, but still keeps some of the old features. Scalability is certainly not affected by it.

We have not had scalability issues. Drupal is designed for complex and large websites.

No issues

I believe the solution is scalable. 

We did encounter some scalability issues when I tried to add custom PHP codes. I searched Google for a solution, but I couldn't find anything.

There were no scalability issues.

We had issues with scalability.

There were no scalability issues. You can scale any part of the project. You can replace some features if you need to.

There have been no scalability issues.

I have had no problems with scalability.

Not yet.