331 lines
14 KiB
Markdown
331 lines
14 KiB
Markdown
---
|
|
stage: none
|
|
group: unassigned
|
|
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments
|
|
---
|
|
|
|
# Working with the GitHub importer
|
|
|
|
In GitLab 10.2 a new version of the GitHub importer was introduced. This new
|
|
importer performs its work in parallel using Sidekiq, greatly reducing the time
|
|
necessary to import GitHub projects into a GitLab instance.
|
|
|
|
The GitHub importer offers two different types of importers: a sequential
|
|
importer and a parallel importer. The Rake task `import:github` uses the
|
|
sequential importer, and everything else uses the parallel importer. The
|
|
difference between these two importers is:
|
|
|
|
- The sequential importer does all the work in a single thread, so it's more suited for debugging purposes or Rake tasks.
|
|
- The parallel importer uses Sidekiq.
|
|
|
|
## Requirements
|
|
|
|
- GitLab CE 10.2.0 or newer.
|
|
- Sidekiq workers that process the `github_importer` and
|
|
`github_importer_advance_stage` queues (this is enabled by default).
|
|
- Octokit (used for interacting with the GitHub API).
|
|
|
|
## Code structure
|
|
|
|
The importer's codebase is broken up into the following directories:
|
|
|
|
- `lib/gitlab/github_import`: this directory contains most of the code such as
|
|
the classes used for importing resources.
|
|
- `app/workers/gitlab/github_import`: this directory contains the Sidekiq
|
|
workers.
|
|
- `app/workers/concerns/gitlab/github_import`: this directory contains a few
|
|
modules reused by the various Sidekiq workers.
|
|
|
|
## Architecture overview
|
|
|
|
When a GitHub project is imported, we schedule and execute a job for the
|
|
`RepositoryImportWorker` worker as all other importers. However, unlike other
|
|
importers, we don't immediately perform the work necessary. Instead work is
|
|
divided into separate stages, with each stage consisting out of a set of Sidekiq
|
|
jobs that are executed. Between every stage a job is scheduled that periodically
|
|
checks if all work of the current stage is completed, advancing the import
|
|
process to the next stage when this is the case. The worker handling this is
|
|
called `Gitlab::GithubImport::AdvanceStageWorker`.
|
|
|
|
## Stages
|
|
|
|
### 1. RepositoryImportWorker
|
|
|
|
This worker starts the import process by scheduling a job for the
|
|
next worker.
|
|
|
|
### 2. Stage::ImportRepositoryWorker
|
|
|
|
This worker imports the repository and wiki, scheduling the next stage when
|
|
done.
|
|
|
|
### 3. Stage::ImportBaseDataWorker
|
|
|
|
This worker imports base data such as labels, milestones, and releases. This
|
|
work is done in a single thread because it can be performed fast enough that we
|
|
don't need to perform this work in parallel.
|
|
|
|
### 4. Stage::ImportPullRequestsWorker
|
|
|
|
This worker imports all pull requests. For every pull request a job for the
|
|
`Gitlab::GithubImport::ImportPullRequestWorker` worker is scheduled.
|
|
|
|
### 5. Stage::ImportPullRequestsMergedByWorker
|
|
|
|
This worker imports the pull requests' _merged-by_ user information. The
|
|
[_List pull requests_](https://docs.github.com/en/rest/pulls#list-pull-requests)
|
|
API doesn't provide this information. Therefore, this stage must fetch each merged pull request
|
|
individually to import this information. A
|
|
`Gitlab::GithubImport::ImportPullRequestMergedByWorker` job is scheduled for each fetched pull
|
|
request.
|
|
|
|
### 6. Stage::ImportPullRequestsReviewRequestsWorker
|
|
|
|
This worker imports assigned reviewers of pull requests. For each pull request, this worker:
|
|
|
|
- Fetches all assigned review requests.
|
|
- Schedules a `Gitlab::GithubImport::PullRequests::ImportReviewRequestWorker` job for each fetched review request.
|
|
|
|
### 7. Stage::ImportPullRequestsReviewsWorker
|
|
|
|
This worker imports reviews of pull requests. For each pull request, this worker:
|
|
|
|
- Fetches all the pages of reviews.
|
|
- Schedules a `Gitlab::GithubImport::ImportPullRequestReviewWorker` job for each fetched review.
|
|
|
|
### 8. Stage::ImportIssuesAndDiffNotesWorker
|
|
|
|
This worker imports all issues and pull request comments. For every issue, we
|
|
schedule a job for the `Gitlab::GithubImport::ImportIssueWorker` worker. For
|
|
pull request comments, we instead schedule jobs for the
|
|
`Gitlab::GithubImport::DiffNoteImporter` worker.
|
|
|
|
This worker processes both issues and diff notes in parallel so we don't need to
|
|
schedule a separate stage and wait for the previous one to complete.
|
|
|
|
Issues are imported separately from pull requests because only the "issues" API
|
|
includes labels for both issue and pull requests. Importing issues and setting
|
|
label links in the same worker removes the need for performing a separate crawl
|
|
through the API data, reducing the number of API calls necessary to import a
|
|
project.
|
|
|
|
### 9. Stage::ImportIssueEventsWorker
|
|
|
|
This worker imports all issues and pull request events. For every event, we
|
|
schedule a job for the `Gitlab::GithubImport::ImportIssueEventWorker` worker.
|
|
|
|
We can import both issues and pull request events by single stage because of a specific aspect of the GitHub API. It looks like that under the hood, issues and pull requests
|
|
GitHub are stored in a single table. Therefore, they have globally-unique IDs and so:
|
|
|
|
- Every pull request is an issue.
|
|
- Issues aren't pull requests.
|
|
|
|
Therefore, both issues and pull requests have a common API for most related things.
|
|
|
|
NOTE:
|
|
This stage is optional and can consume significant extra import time (controlled by `Gitlab::GithubImport::Settings`).
|
|
|
|
### 10. Stage::ImportNotesWorker
|
|
|
|
This worker imports regular comments for both issues and pull requests. For
|
|
every comment, we schedule a job for the
|
|
`Gitlab::GithubImport::ImportNoteWorker` worker.
|
|
|
|
Regular comments have to be imported at the end because the GitHub API used
|
|
returns comments for both issues and pull requests. This means we have to wait
|
|
for all issues and pull requests to be imported before we can import regular
|
|
comments.
|
|
|
|
### 11. Stage::ImportAttachmentsWorker
|
|
|
|
This worker imports note attachments that are linked inside Markdown.
|
|
For each entity with Markdown text in the project, we schedule a job of:
|
|
|
|
- `Gitlab::GithubImport::ImportReleaseAttachmentsWorker` for every release.
|
|
- `Gitlab::GithubImport::ImportNoteAttachmentsWorker` for every note.
|
|
- `Gitlab::GithubImport::ImportIssueAttachmentsWorker` for every issue.
|
|
- `Gitlab::GithubImport::ImportMergeRequestAttachmentsWorker` for every merge request.
|
|
|
|
Each job:
|
|
|
|
1. Iterates over all attachment links inside of a specific record.
|
|
1. Downloads the attachment.
|
|
1. Replaces the old link with a newly-generated link to GitLab.
|
|
|
|
NOTE:
|
|
It's an optional stage that could consume significant extra import time (controlled by `Gitlab::GithubImport::Settings`).
|
|
|
|
### 12. Stage::ImportProtectedBranchesWorker
|
|
|
|
This worker imports protected branch rules.
|
|
For every rule that exists on GitHub, we schedule a job of
|
|
`Gitlab::GithubImport::ImportProtectedBranchWorker`.
|
|
|
|
Each job compares the branch protection rules from GitHub and GitLab and applies
|
|
the strictest of the rules to the branches in GitLab.
|
|
|
|
### 13. Stage::FinishImportWorker
|
|
|
|
This worker completes the import process by performing some housekeeping
|
|
(such as flushing any caches) and by marking the import as completed.
|
|
|
|
## Advancing stages
|
|
|
|
Advancing stages is done in one of two ways:
|
|
|
|
- Scheduling the worker for the next stage directly.
|
|
- Scheduling a job for `Gitlab::GithubImport::AdvanceStageWorker` which will
|
|
advance the stage when all work of the current stage has been completed.
|
|
|
|
The first approach should only be used by workers that perform all their work in
|
|
a single thread, while `AdvanceStageWorker` should be used for everything else.
|
|
|
|
When you schedule a job, `AdvanceStageWorker`
|
|
is given a project ID, a list of Redis keys, and the name of the next
|
|
stage. The Redis keys (produced by `Gitlab::JobWaiter`) are used to check if the
|
|
running stage has been completed or not. If the stage has not yet been
|
|
completed `AdvanceStageWorker` reschedules itself. After a stage finishes
|
|
`AdvanceStageworker` refreshes the import JID (more on this below) and
|
|
schedule the worker of the next stage.
|
|
|
|
To reduce the number of `AdvanceStageWorker` jobs scheduled this worker
|
|
briefly waits for jobs to complete before deciding what the next action should
|
|
be. For small projects, this may slow down the import process a bit, but it
|
|
also reduces pressure on the system as a whole.
|
|
|
|
## Refreshing import job IDs
|
|
|
|
GitLab includes a worker called `Gitlab::Import::StuckProjectImportJobsWorker`
|
|
that periodically runs and marks project imports as failed if they have been
|
|
running for more than 15 hours. For GitHub projects, this poses a bit of a
|
|
problem: importing large projects could take several hours depending on how
|
|
often we hit the GitHub rate limit (more on this below), but we don't want
|
|
`Gitlab::Import::StuckProjectImportJobsWorker` to mark our import as failed because of this.
|
|
|
|
To prevent this from happening we periodically refresh the expiration time of
|
|
the import process. This works by storing the JID of the import job in the
|
|
database, then refreshing this JID TTL at various stages throughout the import
|
|
process. This is done by calling `ProjectImportState#refresh_jid_expiration`. By
|
|
refreshing this TTL we can ensure our import does not get marked as failed so
|
|
long we're still performing work.
|
|
|
|
## GitHub rate limit
|
|
|
|
GitHub has a rate limit of 5,000 API calls per hour. The number of requests
|
|
necessary to import a project is largely dominated by the number of unique users
|
|
involved in a project (for example, issue authors). Other data such as issue pages
|
|
and comments typically only requires a few dozen requests to import. This is
|
|
because we need the Email address of users to map them to GitLab users.
|
|
|
|
We handle this by doing the following:
|
|
|
|
1. After we hit the rate limit all jobs automatically reschedule themselves
|
|
in such a way that they are not executed until the rate limit has been reset.
|
|
1. We cache the mapping of GitHub users to GitLab users in Redis.
|
|
|
|
More information on user caching can be found below.
|
|
|
|
## Caching user lookups
|
|
|
|
When mapping GitHub users to GitLab users we need to (in the worst case)
|
|
perform:
|
|
|
|
1. One API call to get the user's Email address.
|
|
1. Two database queries to see if a corresponding GitLab user exists. One query
|
|
tries to find the user based on the GitHub user ID, while the second query
|
|
is used to find the user using their GitHub Email address.
|
|
|
|
To avoid mismatching users, the search by GitHub user ID is not done when importing from GitHub
|
|
Enterprise.
|
|
|
|
Because this process is quite expensive we cache the result of these lookups in
|
|
Redis. For every user looked up we store three keys:
|
|
|
|
- A Redis key mapping GitHub usernames to their Email addresses.
|
|
- A Redis key mapping a GitHub Email addresses to a GitLab user ID.
|
|
- A Redis key mapping a GitHub user ID to GitLab user ID.
|
|
|
|
There are two types of lookups we cache:
|
|
|
|
- A positive lookup, meaning we found a GitLab user ID.
|
|
- A negative lookup, meaning we didn't find a GitLab user ID. Caching this
|
|
prevents us from performing the same work for users that we know don't exist
|
|
in our GitLab database.
|
|
|
|
The expiration time of these keys is 24 hours. When retrieving the cache of a
|
|
positive lookup, we refresh the TTL automatically. The TTL of false lookups is
|
|
never refreshed.
|
|
|
|
Because of this caching layer, it's possible newly registered GitLab accounts
|
|
aren't linked to their corresponding GitHub accounts. This, however, is resolved
|
|
after the cached keys expire.
|
|
|
|
The user cache lookup is shared across projects. This means that the greater the number of
|
|
projects that are imported, fewer GitHub API calls are needed.
|
|
|
|
The code for this resides in:
|
|
|
|
- `lib/gitlab/github_import/user_finder.rb`
|
|
- `lib/gitlab/github_import/caching.rb`
|
|
|
|
## Mapping labels and milestones
|
|
|
|
To reduce pressure on the database we do not query it when setting labels and
|
|
milestones on issues and merge requests. Instead, we cache this data when we
|
|
import labels and milestones, then we reuse this cache when assigning them to
|
|
issues/merge requests. Similar to the user lookups these cache keys are expired
|
|
automatically after 24 hours of not being used.
|
|
|
|
Unlike the user lookup caches, these label and milestone caches are scoped to the
|
|
project that is being imported.
|
|
|
|
The code for this resides in:
|
|
|
|
- `lib/gitlab/github_import/label_finder.rb`
|
|
- `lib/gitlab/github_import/milestone_finder.rb`
|
|
- `lib/gitlab/github_import/caching.rb`
|
|
|
|
## Logs
|
|
|
|
> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48512/diffs) in GitLab 13.7.
|
|
> - Number of imported objects [introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64256) in GitLab 14.1.
|
|
> - `Gitlab::GithubImport::Logger` [introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/65968) in GitLab 14.2.
|
|
> - `import_source` [renamed](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/67726) to `import_type` in GitLab 14.2.
|
|
|
|
The import progress can be checked in the `logs/importer.log` file. Each relevant import is logged
|
|
with `"import_type": "github"` and the `"project_id"`.
|
|
|
|
The last log entry reports the number of objects fetched and imported:
|
|
|
|
```json
|
|
{
|
|
"message": "GitHub project import finished",
|
|
"duration_s": 347.25,
|
|
"objects_imported": {
|
|
"fetched": {
|
|
"diff_note": 93,
|
|
"issue": 321,
|
|
"note": 794,
|
|
"pull_request": 108,
|
|
"pull_request_merged_by": 92,
|
|
"pull_request_review": 81
|
|
},
|
|
"imported": {
|
|
"diff_note": 93,
|
|
"issue": 321,
|
|
"note": 794,
|
|
"pull_request": 108,
|
|
"pull_request_merged_by": 92,
|
|
"pull_request_review": 81
|
|
}
|
|
},
|
|
"import_source": "github",
|
|
"project_id": 47,
|
|
"import_stage": "Gitlab::GithubImport::Stage::FinishImportWorker"
|
|
}
|
|
```
|
|
|
|
## Metrics dashboards
|
|
|
|
To assess the GitHub importer health, the [GitHub importer dashboard](https://dashboards.gitlab.net/d/importers-github-importer/importers-github-importer)
|
|
provides information about the total number of objects fetched vs. imported over time.
|