There are two software distributions of GitLab: the open source [Community Edition](https://gitlab.com/gitlab-org/gitlab-ce/) (CE), and the open core [Enterprise Edition](https://gitlab.com/gitlab-org/gitlab-ee/) (EE). GitLab is available under [different subscriptions](https://about.gitlab.com/pricing/).
Both EE and CE require some add-on components called gitlab-shell and Gitaly. These components are available from the [gitlab-shell](https://gitlab.com/gitlab-org/gitlab-shell/tree/master) and [gitaly](https://gitlab.com/gitlab-org/gitaly/tree/master) repositories respectively. New versions are usually tags but staying on the master branch will give you the latest stable version. New releases are generally around the same time as GitLab CE releases with exception for informal security updates deemed critical.
A typical install of GitLab will be on GNU/Linux. It uses Nginx or Apache as a web front end to proxypass the Unicorn web server. By default, communication between Unicorn and the front end is via a Unix domain socket but forwarding requests via TCP is also supported. The web front end accesses `/home/git/gitlab/public` bypassing the Unicorn server to serve static pages, uploads (e.g. avatar images or attachments), and precompiled assets. GitLab serves web pages and a [GitLab API](https://gitlab.com/gitlab-org/gitlab-ce/tree/master/doc/api) using the Unicorn web server. It uses Sidekiq as a job queue which, in turn, uses redis as a non-persistent database backend for job information, meta data, and incoming jobs.
The GitLab web app uses PostgreSQL for persistent database information (e.g. users, permissions, issues, other meta data). GitLab stores the bare git repositories it serves in `/home/git/repositories` by default. It also keeps default branch and hook information with the bare repository.
The add-on component gitlab-shell serves repositories over SSH. It manages the SSH keys within `/home/git/.ssh/authorized_keys` which should not be manually edited. gitlab-shell accesses the bare repositories through Gitaly to serve git objects and communicates with redis to submit jobs to Sidekiq for GitLab to process. gitlab-shell queries the GitLab API to determine authorization and access.
Gitaly executes git operations from gitlab-shell and the GitLab web app, and provides an API to the GitLab web app to get attributes from git (e.g. title, branches, tags, other meta data), and to get blobs (e.g. diffs, commits, files).
You may also be interested in the [production architecture of GitLab.com](https://about.gitlab.com/handbook/engineering/infrastructure/production-architecture/).
### Simplified Component Overview
This is a simplified architecture diagram that can be used to
understand GitLab's architecture.
A complete architecture diagram is available in our
| [NGINX](#nginx) | Routes requests to appropriate components, terminates SSL | [✅][nginx-omnibus] | [✅][nginx-charts] | [⚙][nginx-charts] | [✅](https://about.gitlab.com/handbook/engineering/infrastructure/production-architecture/#service-architecture) | [⤓][nginx-source] | ❌ | CE & EE |
| [Unicorn (GitLab Rails)](#unicorn) | Handles requests for the web interface and API | [✅][unicorn-omnibus] | [✅][unicorn-charts] | [✅][unicorn-charts] | [✅](../user/gitlab_com/index.md#unicorn) | [⚙][unicorn-source] | [✅][gitlab-yml] | CE & EE |
| [Sidekiq](#sidekiq) | Background jobs processor | [✅][sidekiq-omnibus] | [✅][sidekiq-charts] | [✅](https://docs.gitlab.com/charts/charts/gitlab/sidekiq/index.html) | [✅](../user/gitlab_com/index.md#sidekiq) | [✅][gitlab-yml] | [✅][gitlab-yml] | CE & EE |
| [Gitaly](#gitaly) | Git RPC service for handling all git calls made by GitLab | [✅][gitaly-omnibus] | [✅][gitaly-charts] | [✅][gitaly-charts] | [✅](https://about.gitlab.com/handbook/engineering/infrastructure/production-architecture/#service-architecture) | [⚙][gitaly-source] | ✅ | CE & EE |
| [GitLab Workhorse](#gitlab-workhorse) | Smart reverse proxy, handles large HTTP requests | [✅][workhorse-omnibus] | [✅][workhorse-charts] | [✅][workhorse-charts] | [✅](https://about.gitlab.com/handbook/engineering/infrastructure/production-architecture/#service-architecture) | [⚙][workhorse-source] | ✅ | CE & EE |
| [GitLab Shell](#gitlab-shell) | Handles `git` over SSH sessions | [✅][shell-omnibus] | [✅][shell-charts] | [✅][shell-charts] | [✅](https://about.gitlab.com/handbook/engineering/infrastructure/production-architecture/#service-architecture) | [⚙][shell-source] | [✅][gitlab-yml] | CE & EE |
| [Sentry integration](#sentry) | Error tracking for deployed apps | [⤓][sentry-integration] | [⤓][sentry-integration] | [⤓][sentry-integration] | [⤓][sentry-integration] | [⤓][sentry-integration] | [⤓][sentry-integration] | CE & EE |
| [Jaeger integration](#jaeger) | Distributed tracing for deployed apps | [⤓][jaeger-integration] | [⤓][jaeger-integration] | [⤓][jaeger-integration] | [⤓][jaeger-integration] | [⤓][jaeger-integration] | [⤓][jaeger-integration] | EE Only |
| [GitLab Managed Apps](#gitlab-managed-apps) | Deploy [Helm](https://docs.helm.sh/), [Ingress](https://kubernetes.io/docs/concepts/services-networking/ingress/), [Cert-Manager](https://docs.cert-manager.io/en/latest/), [Prometheus](https://prometheus.io/docs/introduction/overview/), a [Runner](https://docs.gitlab.com/runner/), [JupyterHub](http://jupyter.org/), [Knative](https://cloud.google.com/knative) to a cluster | [⤓][managed-k8s-apps] | [⤓][managed-k8s-apps] | [⤓][managed-k8s-apps] | [⤓][managed-k8s-apps] | [⤓][managed-k8s-apps] | [⤓][managed-k8s-apps] | CE & EE |
### Component details
This document is designed to be consumed by systems administrators and GitLab Support Engineers who want to understand more about the internals of GitLab and how they work together.
When deployed, GitLab should be considered the amalgamation of the below processes. When troubleshooting or debugging, be as specific as possible as to which component you are referencing. That should increase clarity and reduce confusion.
- **Monitoring**: Anything from this layer is not required to deliver GitLab the application, but will allow administrators more insight into their infrastructure and what the service as a whole is doing.
- **Core**: Any process that is vital for the delivery of GitLab as a platform. If any of these processes halt there will be a GitLab outage. For the Core layer, you can further divide into:
- **Processors**: These processes are responsible for actually performing operations and presenting the service.
- **Data**: These services store/expose structured data for the GitLab service.
[Alert manager](https://prometheus.io/docs/alerting/alertmanager/) is a tool provided by Prometheus that _"handles alerts sent by client applications such as the Prometheus server. It takes care of deduplicating, grouping, and routing them to the correct receiver integration such as email, PagerDuty, or OpsGenie. It also takes care of silencing and inhibition of alerts."_ You can read more in [issue gitlab-ce#45740](https://gitlab.com/gitlab-org/gitlab-ce/issues/45740) about what we will be alerting on.
Gitaly is a service designed by GitLab to remove our need for NFS for Git storage in distributed deployments of GitLab (think GitLab.com or High Availability Deployments). As of 11.3.0, this service handles all Git level access in GitLab. You can read more about the project [in the project's readme](https://gitlab.com/gitlab-org/gitaly).
GitLab Monitor is a process designed in house that allows us to export metrics about GitLab application internals to Prometheus. You can read more [in the project's readme](https://gitlab.com/gitlab-org/gitlab-monitor).
GitLab Pages is a feature that allows you to publish static websites directly from a repository in GitLab.
You can use it either for personal or business websites, such as portfolios, documentation, manifestos, and business presentations. You can also attribute any license to your content.
GitLab CI is the open-source continuous integration service included with GitLab that coordinates the testing. The old name of this project was GitLab CI Multi Runner but please use "GitLab Runner" (without CI) from now on.
[GitLab Shell](https://gitlab.com/gitlab-org/gitlab-shell) is a program designed at GitLab to handle ssh-based `git` sessions, and modifies the list of authorized keys. GitLab Shell is not a Unix shell nor a replacement for Bash or Zsh.
[GitLab Workhorse](https://gitlab.com/gitlab-org/gitlab-workhorse) is a program designed at GitLab to help alleviate pressure from Unicorn. You can read more about the [historical reasons for developing](https://about.gitlab.com/2016/04/12/a-brief-history-of-gitlab-workhorse/). It's designed to act as a smart reverse proxy to help speed up GitLab as a whole.
GitLab is comprised of a large number of services that all log. We started bundling our own logrotate as of 7.4 to make sure we were logging responsibly. This is just a packaged version of the common open source offering.
MinIO is an object storage server released under Apache License v2.0. It is compatible with Amazon S3 cloud storage service. It is best suited for storing unstructured data such as photos, videos, log files, backups and container / VM images. Size of an object can range from a few KBs to a maximum of 5TB.
Nginx as an ingress port for all HTTP requests and routes them to the appropriate sub-systems within GitLab. We are bundling an unmodified version of the popular open source webserver.
[Node Exporter](https://github.com/prometheus/node_exporter) is a Prometheus tool that gives us metrics on the underlying machine (think CPU/Disk/Load). It's just a packaged version of the common open source offering from the Prometheus project.
[Postgres-exporter](https://github.com/wrouesnel/postgres_exporter) is the community provided Prometheus exporter that will deliver data about Postgres to Prometheus for use in Grafana Dashboards.
[Redis Exporter](https://github.com/oliver006/redis_exporter) is designed to give specific metrics about the Redis process to Prometheus so that we can graph these metrics in Grafana.
Sentry fundamentally is a service that helps you monitor and fix crashes in realtime. The server is in Python, but it contains a full API for sending events from any language, in any application.
Sidekiq is a Ruby background job processor that pulls jobs from the redis queue and processes them. Background jobs allow GitLab to provide a faster request/response cycle by moving work into the background.
[Unicorn](https://bogomips.org/unicorn/) is a Ruby application server that is used to run the core Rails Application that provides the user facing features in GitLab. Often process output you will see this as `bundle` or `config.ru` depending on the GitLab version.
GitLab provides [GitLab Managed Apps](../user/project/clusters/index.md#installing-applications), a one-click install for various applications which can be added directly to your configured cluster. These applications are needed for Review Apps and deployments when using Auto DevOps. You can install them after you create a cluster.
Below we describe the different pathing that HTTP vs. SSH Git requests will take. There is some overlap with the Web Request Cycle but also some differences.
GitLab is primarily installed within the `/home/git` user home directory as `git` user. Within the home directory is where the gitlabhq server software resides as well as the repositories (though the repository location is configurable).
The bare repositories are located in `/home/git/repositories`. GitLab is a ruby on rails application so the particulars of the inner workings can be learned by studying how a ruby on rails application works.
To serve repositories over SSH there's an add-on application called gitlab-shell which is installed in `/home/git/gitlab-shell`.
### Installation Folder Summary
To summarize here's the [directory structure of the `git` user home directory](../install/structure.md).
Repositories get accessed via HTTP or SSH. HTTP cloning/push/pull utilizes the GitLab API and SSH cloning is handled by gitlab-shell (previously explained).
## Troubleshooting
See the README for more information.
### Init scripts of the services
The GitLab init script starts and stops Unicorn and Sidekiq.
```
/etc/init.d/gitlab
Usage: service gitlab {start|stop|restart|reload|status}
GitLab has configuration files located in `/home/git/gitlab/config/*`. Commonly referenced config files include:
-`gitlab.yml` - GitLab configuration.
-`unicorn.rb` - Unicorn web server settings.
-`database.yml` - Database connection settings.
gitlab-shell has a configuration file at `/home/git/gitlab-shell/config.yml`.
### Maintenance Tasks
[GitLab](https://gitlab.com/gitlab-org/gitlab-ce/tree/master) provides rake tasks with which you see version information and run a quick check on your configuration to ensure it is configured properly within the application. See [maintenance rake tasks](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/raketasks/maintenance.md).
Note: It is recommended to log into the `git` user using `sudo -i -u git` or `sudo su - git`. While the sudo commands provided by gitlabhq work in Ubuntu they do not always work in RHEL.
We've also detailed [our architecture of GitLab.com](https://about.gitlab.com/handbook/engineering/infrastructure/production-architecture/) but this is probably over the top unless you have millions of users.
