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gitlab-org--gitlab-foss/doc/user/project/import/github.md
Yorick Peterse 4dfe26cd8b
Rewrite the GitHub importer from scratch 
Prior to this MR there were two GitHub related importers:

* Github::Import: the main importer used for GitHub projects
* Gitlab::GithubImport: importer that's somewhat confusingly used for
  importing Gitea projects (apparently they have a compatible API)

This MR renames the Gitea importer to Gitlab::LegacyGithubImport and
introduces a new GitHub importer in the Gitlab::GithubImport namespace.
This new GitHub importer uses Sidekiq for importing multiple resources
in parallel, though it also has the ability to import data sequentially
should this be necessary.

The new code is spread across the following directories:

* lib/gitlab/github_import: this directory contains most of the importer
  code such as the classes used for importing resources.
* app/workers/gitlab/github_import: this directory contains the Sidekiq
  workers, most of which simply use the code from the directory above.
* app/workers/concerns/gitlab/github_import: this directory provides a
  few modules that are included in every GitHub importer worker.

== Stages

The import work is divided into separate stages, with each stage
importing a specific set of data. Stages will schedule the work that
needs to be performed, followed by scheduling a job for the
"AdvanceStageWorker" worker. This worker will periodically check if all
work is completed and schedule the next stage if this is the case. If
work is not yet completed this worker will reschedule itself.

Using this approach we don't have to block threads by calling `sleep()`,
as doing so for large projects could block the thread from doing any
work for many hours.

== Retrying Work

Workers will reschedule themselves whenever necessary. For example,
hitting the GitHub API's rate limit will result in jobs rescheduling
themselves. These jobs are not processed until the rate limit has been
reset.

== User Lookups

Part of the importing process involves looking up user details in the
GitHub API so we can map them to GitLab users. The old importer used
an in-memory cache, but this obviously doesn't work when the work is
spread across different threads.

The new importer uses a Redis cache and makes sure we only perform
API/database calls if absolutely necessary.  Frequently used keys are
refreshed, and lookup misses are also cached; removing the need for
performing API/database calls if we know we don't have the data we're
looking for.

== Performance & Models

The new importer in various places uses raw INSERT statements (as
generated by `Gitlab::Database.bulk_insert`) instead of using Rails
models. This allows us to bypass any validations and callbacks,
drastically reducing the number of SQL queries and Gitaly RPC calls
necessary to import projects.

To ensure the code produces valid data the corresponding tests check if
the produced rows are valid according to the model validation rules.
2017-11-07 23:24:59 +01:00

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Import your project from GitHub to GitLab

Import your projects from GitHub to GitLab with minimal effort.

Overview

Note: If you are an administrator you can enable the GitHub integration in your GitLab instance sitewide. This configuration is optional, users will still be able to import their GitHub repositories with a personal access token.

Note: Administrators of a GitLab instance (Community or Enterprise Edition) can also use the GitHub rake task to import projects from GitHub without the constrains of a Sidekiq worker.

  • At its current state, GitHub importer can import:
    • the repository description (GitLab 7.7+)
    • the Git repository data (GitLab 7.7+)
    • the issues (GitLab 7.7+)
    • the pull requests (GitLab 8.4+)
    • the wiki pages (GitLab 8.4+)
    • the milestones (GitLab 8.7+)
    • the labels (GitLab 8.7+)
    • the release note descriptions (GitLab 8.12+)
    • the pull request review comments (GitLab 10.2+)
    • the regular issue and pull request comments
  • References to pull requests and issues are preserved (GitLab 8.7+)
  • Repository public access is retained. If a repository is private in GitHub it will be created as private in GitLab as well.

How it works

When issues/pull requests are being imported, the GitHub importer tries to find the GitHub author/assignee in GitLab's database using the GitHub ID. For this to work, the GitHub author/assignee should have signed in beforehand in GitLab and associated their GitHub account. If the user is not found in GitLab's database, the project creator (most of the times the current user that started the import process) is set as the author, but a reference on the issue about the original GitHub author is kept.

The importer will create any new namespaces (groups) if they don't exist or in the case the namespace is taken, the repository will be imported under the user's namespace that started the import process.

The importer will also import branches on forks of projects related to open pull requests. These branches will be imported with a naming scheme similar to GH-SHA-Username/Pull-Request-number/fork-name/branch. This may lead to a discrepency in branches compared to the GitHub Repository.

For a more technical description and an overview of the architecture you can refer to Working with the GitHub importer.

Importing your GitHub repositories

The importer page is visible when you create a new project.

New project page on GitLab

Click on the GitHub link and the import authorization process will start. There are two ways to authorize access to your GitHub repositories:

  1. Using the GitHub integration (if it's enabled by your GitLab administrator). This is the preferred way as it's possible to preserve the GitHub authors/assignees. Read more in the How it works section.
  2. Using a personal access token provided by GitHub.

Select authentication method

Authorize access to your repositories using the GitHub integration

If the GitHub integration is enabled by your GitLab administrator, you can use it instead of the personal access token.

  1. First you may want to connect your GitHub account to GitLab in order for the username mapping to be correct.
  2. Once you connect GitHub, click the List your GitHub repositories button and you will be redirected to GitHub for permission to access your projects.
  3. After accepting, you'll be automatically redirected to the importer.

You can now go on and select which repositories to import.

Authorize access to your repositories using a personal access token

Note: For a proper author/assignee mapping for issues and pull requests, the GitHub integration should be used instead of the personal access token. If the GitHub integration is enabled by your GitLab administrator, it should be the preferred method to import your repositories. Read more in the How it works section.

If you are not using the GitHub integration, you can still perform a one-off authorization with GitHub to grant GitLab access your repositories:

  1. Go to https://github.com/settings/tokens/new.
  2. Enter a token description.
  3. Check the repo scope.
  4. Click Generate token.
  5. Copy the token hash.
  6. Go back to GitLab and provide the token to the GitHub importer.
  7. Hit the List Your GitHub Repositories button and wait while GitLab reads your repositories' information. Once done, you'll be taken to the importer page to select the repositories to import.

Select which repositories to import

After you've authorized access to your GitHub repositories, you will be redirected to the GitHub importer page.

From there, you can see the import statuses of your GitHub repositories.

  • Those that are being imported will show a started status,
  • those already successfully imported will be green with a done status,
  • whereas those that are not yet imported will have an Import button on the right side of the table.

If you want, you can import all your GitHub projects in one go by hitting Import all projects in the upper left corner.

GitHub importer page

You can also choose a different name for the project and a different namespace, if you have the privileges to do so.

Making the import process go faster

For large projects it may take a while to import all data. To reduce the time necessary you can increase the number of Sidekiq workers that process the following queues:

  • github_importer
  • github_importer_advance_stage

For an optimal experience we recommend having at least 4 Sidekiq processes (each running a number of threads equal to the number of CPU cores) that only process these queues. We also recommend that these processes run on separate servers. For 4 servers with 8 cores this means you can import up to 32 objects (e.g. issues) in parallel.

Reducing the time spent in cloning a repository can be done by increasing network throughput, CPU capacity, and disk performance (e.g. by using high performance SSDs) of the disks that store the Git repositories (for your GitLab instance). Increasing the number of Sidekiq workers will not reduce the time spent cloning repositories.