# 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 will be set for the different GitLab tiers. You also need to
coordinate with others to [document](../administration/instance_limits.md)
and communicate those limits.

There is a guide about [introducing application
limits](https://about.gitlab.com/handbook/product/product-processes/#introducing-application-limits).

## Development

### Insert database plan limits

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

1. Add new column to the `plan_limits` table with non-null default value
   that represents desired limit, such as:

  ```ruby
  add_column(:plan_limits, :project_hooks, :integer, default: 100, null: false)
  ```

  NOTE: **Note:**
  Plan limits entries set to `0` mean that limits are not
  enabled. You should use this setting only in special and documented circumstances.

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

  ```ruby
  class InsertProjectHooksPlanLimits < ActiveRecord::Migration[5.2]
    include Gitlab::Database::MigrationHelpers

    DOWNTIME = false

    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', 'gold', 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', 'gold', 0)
    end
  end
  ```

NOTE: **Note:**
Some plans exist only on GitLab.com. This will be 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:

```ruby
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:

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

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

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

#### `Limitable` concern

The [`Limitable` concern](https://gitlab.com/gitlab-org/gitlab/blob/master/app/models/concerns/limitable.rb)
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.

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

```ruby
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.

```ruby
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.

```ruby
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

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
- `silver` - Namespaces and projects with a Silver subscription
- `gold` - Namespaces and projects with a Gold subscription

NOTE: **Note:**
The test environment doesn't have any plans.
