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# Adding a new Service Component to GitLab
The GitLab product is made up of several service components that run as independent system processes in communication with each other. These services can be run on the same instance, or spread across different instances. A list of the existing components can be found in the [GitLab architecture overview](architecture.md).
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# API style guide
This style guide recommends best practices for API development.
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# Application secrets
This page is a development guide for application secrets.
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# Approval Rules **(STARTER)**
This document explains the backend design and flow of all related functionality
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# Generating chaos in a test GitLab instance
As [Werner Vogels](https://twitter.com/Werner), the CTO at Amazon Web Services, famously put it, **Everything fails, all the time**.
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# Code comments
Whenever you add comment to the code that is expected to be addressed at any time
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# Creating enums
When creating a new enum, it should use the database type `SMALLINT`.
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# Deprecation guidelines
This page includes information about how and when to remove or make breaking
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# Guidelines for implementing Enterprise Edition features
-**Write the code and the tests.**: As with any code, EE features should have
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# Dealing with email in development
## Ensuring compatibility with mailer Sidekiq jobs
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# Experiment Guide
Experiments can be conducted by any GitLab team, most often the teams from the [Growth Sub-department](https://about.gitlab.com/handbook/engineering/development/growth/). Experiments are not tied to releases because they will primarily target GitLab.com.
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# Architecture
When you are developing a new feature that requires architectural design, or if
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# Axios
We use [Axios](https://github.com/axios/axios) to communicate with the server in Vue applications and most new code.
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# Frontend Development Process
You can find more about the organization of the frontend team in the [handbook](https://about.gitlab.com/handbook/engineering/frontend/).
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# DropLab
A generic dropdown for all of your custom dropdown needs.
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# Ajax
`Ajax` is a droplab plugin that allows for retrieving and rendering list data from a server.
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# Filter
`Filter` is a plugin that allows for filtering data that has been added
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# InputSetter
`InputSetter` is a plugin that allows for updating DOM out of the scope of droplab when a list item is clicked.
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# Emojis
GitLab supports native Unicode emojis and falls back to image-based emojis selectively
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# Icons and SVG Illustrations
We manage our own icon and illustration library in the [`gitlab-svgs`](https://gitlab.com/gitlab-org/gitlab-svgs)
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# Frontend Development Guidelines
This document describes various guidelines to ensure consistency and quality
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# Implementing keyboard shortcuts
We use [Mousetrap](https://craig.is/killing/mice) to implement keyboard
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# Principles
These principles will ensure that your frontend contribution starts off in the right direction.
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# GitLab development style guides
See below for the relevant style guides, guidelines, linting, and other information for developing GitLab.
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# Vue
To get started with Vue, read through [their documentation](https://vuejs.org/v2/guide/).
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# Migration to Vue 3
In order to prepare for the eventual migration to Vue 3.x, we should be wary about adding the following features to the codebase:
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# Vuex
When there's a clear benefit to separating state management from components (e.g. due to state complexity) we recommend using [Vuex](https://vuex.vuejs.org) over any other Flux pattern. Otherwise, feel free to manage state within the components.
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# File Storage in GitLab
We use the [CarrierWave](https://github.com/carrierwaveuploader/carrierwave) gem to handle file upload, store and retrieval.
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# Dependency Management in Go
Go takes an unusual approach to dependency management, in that it is
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# Gotchas
The purpose of this guide is to document potential "gotchas" that contributors
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# GraphQL development guidelines
This guide contains all the information to successfully contribute to GitLab's
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# Hash Indexes
PostgreSQL supports hash indexes besides the regular B-tree
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# Internationalization for GitLab
> [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10669) in GitLab 9.2.
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# Translate GitLab to your language
The text in GitLab's user interface is in American English by default.
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# Merging translations from CrowdIn
CrowdIn automatically syncs the `gitlab.pot` file with the CrowdIn service, presenting
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# Proofread Translations
Most translations are contributed, reviewed, and accepted by the community. We
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# Translating GitLab
For managing the translation process we use [CrowdIn](https://crowdin.com).
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# Import/Export development documentation
Troubleshooting and general development guidelines and tips for the [Import/Export feature](../user/project/settings/import_export.md).
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# Test Import Project
For testing, we can import our own [GitLab CE](https://gitlab.com/gitlab-org/gitlab-foss/) project (named `gitlabhq` in this case) under a group named `qa-perf-testing`. Project tarballs that can be used for testing can be found over on the [performance-data](https://gitlab.com/gitlab-org/quality/performance-data) project. A different project could be used if required.
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# Setting up a development environment
The following are required to install and test the app:
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# Iterating Tables In Batches
Rails provides a method called `in_batches` that can be used to iterate over
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# Licensed feature availability **(STARTER)**
As of GitLab 9.4, we've been supporting a simplified version of licensed
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# GitLab Licensing and Compatibility
[GitLab Community Edition](https://gitlab.com/gitlab-org/gitlab-foss/)(CE) is licensed [under the terms of the MIT License](https://gitlab.com/gitlab-org/gitlab-foss/blob/master/LICENSE). [GitLab Enterprise Edition](https://gitlab.com/gitlab-org/gitlab/)(EE) is licensed under "[The GitLab Enterprise Edition (EE) license](https://gitlab.com/gitlab-org/gitlab/blob/master/LICENSE)" wherein there are more restrictions.
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# Database case study: Namespaces storage statistics
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# Accessibility
Using semantic HTML plays a key role when it comes to accessibility.
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# Frontend Development Guidelines
This guide contains all the information to successfully contribute to GitLab's frontend.
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# Dirty Submit
> [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/21115) in GitLab 11.3.
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# Merge request widget extensions
> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/44616) in GitLab 13.6.
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# Newlines style guide
This style guide recommends best practices for newlines in Ruby code.
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# Post Deployment Migrations
Post deployment migrations are regular Rails migrations that can optionally be
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# Query Count Limits
Each controller or API endpoint is allowed to execute up to 100 SQL queries and
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# QueryRecorder
QueryRecorder is a tool for detecting the [N+1 queries problem](https://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations) from tests.
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# Rails initializers
By default, Rails loads Zeitwerk after the initializers in `config/initializers` are loaded.
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# `ReactiveCaching`
> This doc refers to <https://gitlab.com/gitlab-org/gitlab/blob/master/app/models/concerns/reactive_caching.rb>.
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# Renaming features
Sometimes the business asks to change the name of a feature. Broadly speaking, there are 2 approaches to that task. They basically trade between immediate effort and future complexity/bug risk:
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# Routing
The GitLab backend is written primarily with Rails so it uses [Rails
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# GitLab scalability
This section describes the current architecture of GitLab as it relates to
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# GitLab Developers Guide to service measurement
You can enable service measurement in order to debug any slow service's execution time, number of SQL calls, garbage collection stats, memory usage, etc.
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# Accessing session data
Session data in GitLab is stored in Redis and can be accessed in a variety of ways.
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# Shared files
Historically, GitLab has been storing shared files in many different
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# Sidekiq Style Guide
This document outlines various guidelines that should be followed when adding or
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# Dynamic Element Validation
We devised a solution to solve common test automation problems such as the dreaded `NoSuchElementException`.
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# Environment selection
Some tests are designed to be run against specific environments or [pipelines](https://about.gitlab.com/handbook/engineering/quality/guidelines/debugging-qa-test-failures/#scheduled-qa-test-pipelines).
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# Testing with feature flags
To run a specific test with a feature flag enabled you can use the `QA::Runtime::Feature` class to
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# Flows in GitLab QA
Flows are frequently used sequences of actions. They are a higher level
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# Page objects in GitLab QA
In GitLab QA we are using a known pattern, called _Page Objects_.
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# Resource class in GitLab QA
Resources are primarily created using Browser UI steps, but can also
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# RSpec metadata for end-to-end tests
This is a partial list of the [RSpec metadata](https://relishapp.com/rspec/rspec-core/docs/metadata/user-defined-metadata)
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# Style guide for writing end-to-end tests
This document describes the conventions used at GitLab for writing End-to-end (E2E) tests using the GitLab QA project.
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# Frontend testing standards and style guidelines
There are two types of test suites you'll encounter while developing frontend code
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# Testing standards and style guidelines
This document describes various guidelines and best practices for automated
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# Smoke Tests
It is imperative in any testing suite that we have Smoke Tests. In short, smoke
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# Testing Rake tasks
To make testing Rake tasks a little easier, there is a helper that can be included
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# Understanding EXPLAIN plans
PostgreSQL allows you to obtain query plans using the `EXPLAIN` command. This
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# What requires downtime?
When working with a database certain operations can be performed without taking