Application limits development

This document provides a development guide for contributors to add application limits to GitLab.

Documentation

First of all, you have to gather information and decide which are the different limits that are set for the different GitLab tiers. Coordinate with others to document and communicate those limits.

There is a guide about introducing application limits.

Implement plan limits

Insert database plan limits

In the plan_limits table, create a new column and insert the limit values. It's recommended to create two separate migration script files.

Add a new column to the plan_limits table with non-null default value that represents desired limit, such as:
```
add_column(:plan_limits, :project_hooks, :integer, default: 100, null: false)
```
Plan limits entries set to 0 mean that limits are not enabled. You should use this setting only in special and documented circumstances.

(Optionally) Create the database migration that fine-tunes each level with a desired limit using create_or_update_plan_limit migration helper, such as:

class InsertProjectHooksPlanLimits < Gitlab::Database::Migration[1.0]
  def up
    create_or_update_plan_limit('project_hooks', 'default', 0)
    create_or_update_plan_limit('project_hooks', 'free', 10)
    create_or_update_plan_limit('project_hooks', 'bronze', 20)
    create_or_update_plan_limit('project_hooks', 'silver', 30)
    create_or_update_plan_limit('project_hooks', 'premium', 30)
    create_or_update_plan_limit('project_hooks', 'premium_trial', 30)
    create_or_update_plan_limit('project_hooks', 'gold', 100)
    create_or_update_plan_limit('project_hooks', 'ultimate', 100)
    create_or_update_plan_limit('project_hooks', 'ultimate_trial', 100)
  end

  def down
    create_or_update_plan_limit('project_hooks', 'default', 0)
    create_or_update_plan_limit('project_hooks', 'free', 0)
    create_or_update_plan_limit('project_hooks', 'bronze', 0)
    create_or_update_plan_limit('project_hooks', 'silver', 0)
    create_or_update_plan_limit('project_hooks', 'premium', 0)
    create_or_update_plan_limit('project_hooks', 'premium_trial', 0)
    create_or_update_plan_limit('project_hooks', 'gold', 0)
    create_or_update_plan_limit('project_hooks', 'ultimate', 0)
    create_or_update_plan_limit('project_hooks', 'ultimate_trial', 0)
  end
end

Some plans exist only on GitLab.com. This is a no-op for plans that do not exist.

Plan limits validation

Get current limit

Access to the current limit can be done through the project or the namespace, such as:

project.actual_limits.project_hooks

Check current limit

There is one method PlanLimits#exceeded? to check if the current limit is being exceeded. You can use either an ActiveRecord object or an Integer.

Ensures that the count of the records does not exceed the defined limit, such as:

project.actual_limits.exceeded?(:project_hooks, ProjectHook.where(project: project))

Ensures that the number does not exceed the defined limit, such as:

project.actual_limits.exceeded?(:project_hooks, 10)

`Limitable` concern

The Limitable concern can be used to validate that a model does not exceed the limits. It ensures that the count of the records for the current model does not exceed the defined limit.

You must specify the limit scope of the object being validated and the limit name if it's different from the pluralized model name.

class ProjectHook
  include Limitable

  self.limit_name = 'project_hooks' # Optional as ProjectHook corresponds with project_hooks
  self.limit_scope = :project
end

To test the model, you can include the shared examples.

it_behaves_like 'includes Limitable concern' do
  subject { build(:project_hook, project: create(:project)) }
end

Testing instance-wide limits

Instance-wide features always use default Plan, as instance-wide features do not have license assigned.

class InstanceVariable
  include Limitable

  self.limit_name = 'instance_variables' # Optional as InstanceVariable corresponds with instance_variables
  self.limit_scope = Limitable::GLOBAL_SCOPE
end

Subscription Plans

The opensource plan was introduced in GitLab 14.7.

Self-managed:

default: Everyone.

GitLab.com:

default: Any system-wide feature.
free: Namespaces and projects with a Free subscription.
bronze: Namespaces and projects with a Bronze subscription. This tier is no longer available for purchase.
silver: Namespaces and projects with a Premium subscription.
premium: Namespaces and projects with a Premium subscription.
premium_trial: Namespaces and projects with a Premium Trial subscription.
gold: Namespaces and projects with an Ultimate subscription.
ultimate: Namespaces and projects with an Ultimate subscription.
ultimate_trial: Namespaces and projects with an Ultimate Trial subscription.
opensource: Namespaces and projects that are member of GitLab Open Source program.

The test environment doesn't have any plans.

Implement rate limits using `Rack::Attack`

We use the Rack::Attack middleware to throttle Rack requests. This applies to Rails controllers, Grape endpoints, and any other Rack requests.

The process for adding a new throttle is loosely:

Add new columns to the ApplicationSetting model (*_enabled, *_requests_per_period, *_period_in_seconds).
Extend Gitlab::RackAttack and Gitlab::RackAttack::Request to configure the new rate limit, and apply it to the desired requests.
Add the new settings to the Admin Area form in app/views/admin/application_settings/_ip_limits.html.haml.
Document the new settings in User and IP rate limits and Application settings API.
Configure the rate limit for GitLab.com and document it in GitLab.com-specific rate limits.

Refer to these past issues for implementation details:

Implement rate limits using `Gitlab::ApplicationRateLimiter`

This module implements a custom rate limiter that can be used to throttle certain actions. Unlike Rack::Attack and Rack::Throttle, which operate at the middleware level, this can be used at the controller or API level.

See the CheckRateLimit concern for use in controllers. In other parts of the code the Gitlab::ApplicationRateLimiter module can be called directly.

Next rate limiting architecture

In May 2022 we've started working on the next iteration of our application limits framework using a forward looking rate limiting architecture.

We are working on defining new requirements and designing the next architecture, so if you need new functionalities to add new limits, instead of building them right now, consider contributing to the Rate Limiting Architecture Working Group

Examples of what features we might want to build into the next iteration of rate limiting architecture:

Making it possible to define and override limits per namespace / per plan.
Automatically generating documentation about what limits are implemented and what the defaults are.
Defining limits in a single place that can be found and explored.
Soft and hard limits, with support for notifying users when a limit is approaching.