When and how to grow and shrink your Apps resources.

One of the fortrabbit platform fundamentals is scalability – handle nearly any amount of visitors. Start with low resources and grow wild at any time, increase or decrease computing resources on demand. Each App on fortrabbit has multiple Components which can be scaled individually.

Understanding vertical & horizontal scaling

 # Vertical scaling: grow Node
 # Horizontal scaling: add Nodes

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 │      │      │ │             │ │             │ │             │
 │      │      │ │             │ │             │ │             │
 ├──────┼──────┤ │             │ │             │ │             │
 │      │      │
 │      │      │ │             │ │             │ │             │
 │      │      │
 │      └──────┼─┼─────────────┼─┼─────────────┼─┼──────▶      │
 │             │
 │             │ │             │ │             │ │             │
 │             │
 └─────────────┘ └ ─ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ─ ┘ └ ─ ─ ─ ─ ─ ─ ┘

A Node is a lightweight virtual container that is configured to run a specific service.

Vertical scaling

Vertical scaling means that you grow your Node size. On fortrabbit this mostly means more memory, but also more CPU power. Which vertical scaling size for which Component your App needs depends in large parts on the technology you are using.

Horizontal scaling

Horizontal scaling means that you add more Nodes. Once you have figured out which plan size fits your application best, you can just add more Nodes to your App by booking higher plans: Say your App runs on PHP s, then, with increasing visitors, you simply would scale: PHP s 1 -> PHP s 2 -> PHP s 4 and so on.

To make things easier for you, we categorized most Components into the scaling groups (extension levels), which reflect a point in life of your application. It's mostly best practice to combine Components from the same scaling groups, everything on Production level grade, for example, but it depends on the use case.


Use this for tinkering, in development, as staging environment or for low volume/traffic Apps. This level keeps things simple and affordable by saving on availability and performance.

# Tinkering level scaling App example
┌────────┐     ┌────────┐     ┌─────────┐     ┌─────────┐
│Internet├─────▶ Apache ├─────▶ PHP/FPM ├─────▶  MySQL  │
└────────┘     └────────┘     └─────────┘     └─────────┘


Use for live web applications, for which performance and high availability is key.

# Production & Dedicated level scaling App
               ┌──────────┐   ┌────────┐   ┌─────────┐   ┌──────────────────┐
               │          ├───▶ Apache ├───▶ PHP/FPM ├───▶  MySQL Cluster   │┐ <------`
               │          ││  └────────┘   └─────────┘   └──────────────────┘│        |
┌────────┐     │   Load   ││                    │         └───── ▲ ──────────┘        |
│Internet├─────▶ Balancer ││                    ├────────────────┤                  Worker
└────────┘     │ Cluster  ││                    │                ▼                    |
               │          ││  ┌────────┐   ┌─────────┐   ┌──────────────────┐         |
               │          ├───▶ Apache ├───▶ PHP/FPM ├───▶ Memcache Cluster │┐<-------`
               └──────────┘│  └────────┘   └─────────┘   └──────────────────┘│
                 └─────────┘                              └──────────────────┘


For those lucky few wildly successful web applications. Dedicated private cloud resources give you more control and of course ultimate power.

When to grow horizontally

There are three common scenarios which require a scalable, elastic, environment:

Continuous growth: Your business grows constantly. You should be able to anticipate the acceleration of the growth because you are planning for it and actively take actions to increase and guide it.

Event based: You might have an e-shop, and the Christmas sales are coming. Or you promote a festival, which is once or twice a year. Those events are strongly connected to your business and you plan on them.

Slashdot effect: An extraordinary event occurs — you've been mentioned on a major news site (hackernews, product hunt …) or a television channel is reporting about you. In short: you haven't planned for this.

Our scaling capabilities are focused on the first two scenarios, because the slashdot events are quite rare and - well - unforeseeable by nature. There is no auto-scaling in place, but you can easily and quickly react on traffic peaks by logging into the Dashboard and scaling the App — scaling happens almost immediately.

Comparing with metrics

The fortrabbit Dashboard provides you with useful performance metrics on how your App is doing, what it is handling and how much memory it consumes. This can help you fine tune for the best scaling settings.

How to scale

That's the easiest part: login to the Dashboard, go to your App, click on the Component you want to scale and choose a new scaling. Scaling happens almost instantly and can easily be reversed. The minimum billing period of one day makes it easy to experiment with different settings. Try out a higher scaling level for a day, and you'll only be charged for one day. Scaling happens within minutes, in most cases without downtime.

What to scale

So what is there to scale? Given a typical PHP web application, you have these main resources (we call them Components) to scale individually:


PHP is the main Component on fortrabbit, you can scale it vertically and horizontally. Please see our dedicated article on PHP.


While PHP implements the logic, the MySQL database (most of the time) contains the data the logic works on. Each database has physical limits (disk performance, amount of memory, available CPUs).

You should choose a MySQL plan which has at least as many connections as your PHP plan offers processes. An overview of processes per PHP plan and connections per MySQL plan can be found in our specs table.

All Production and Dedicated MySQL scaling are replicated. This means: they run on two MySQL Nodes at the same time. One of those Nodes is called "master", the other "slave". The master Node is the active Nodes, to which your App automatically connects to. If the master fails then the slave takes automatically over and your App keeps running.

Also see the quirk when scaling MySQL with persistent connections.


Memcache is a Component which can be booked optionally. Memcache is recommended in addition to all PHP production scalings to store session data across Nodes.

Production level Memcache scalings run on two Nodes. Now it depends on how you use/configure your Memcache client. You can either use both Nodes as a single, joined space, which gives you double the memory, or you can use them redundantly, which leaves you with half of that. Only the latter case will provide high availability, since it allows the failure of one of the two Nodes. See also the main Memcache article.


Workers help to offload compute intensive tasks, they can be booked optionally.

All worker plans run only on a single Node. In case one of those Nodes fails they are restarted automatically. This does not guarantee high availability but eventual availability, which is in almost all cases a good approach for executing background tasks. See also the main Workers article.

Object Storage

Professional Apps have an ephemeral local storage, which means that all files on the server will be wiped on each deploy or change of configuration, also on maintenance.

Content driven websites usually make use of the local file system to store assets. If you have a "media website" or an social community focused on image or videos for example, the storage needs to be able to scale as well. For those use cases we recommend to use our Object Storage component. It's easy to setup, supports best practices and reduces load on the PHP Nodes.

The Object Storage plans are limited by storage (not traffic). It will not scale automatically, you need to keep an eye on the size. In the App overview in the Dashboard you can find a graph that shows you home much storage within the current plan is in use. Scaling up and down can (almost) instantly be done in the Dashboard.

Clean code saves money

We are in this together. The smarter you code, the less resources you'll need. Or to put it in more dramatic words: bad code doesn't scale. So please don't miss our application design and coding practices article. Also the limits article to understand what happens when your App is exceeding those.

Advanced specifications

Our specs page provides you with fine-grained information about plans and limits.

General scaling tips

  • It may takes up to 45 minutes until a scaling is applied after booking.
    • New hardware may need to be allocated and data needs to copied.
    • Only when everything is ready, the new resources will be used.
  • Scaling between plans should only cause seconds or no downtime at all.
  • In edge cases hanging "PHP processes" can extend downtime to minutes.
  • The actual execution of the scaling happens postponed. Usually a few minutes after booking the plan.
  • Required scaling is very unique to your application.
  • Experiment with the settings that are best working good for you.
  • Experimenting with scaling settings is not cost-intensive, thanks to daily billing.

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