# Geo Replication **[PREMIUM ONLY]**

Geo is the solution for widely distributed development teams.

## Overview

Fetching large repositories can take a long time for teams located far from a single GitLab instance.

Geo provides local, read-only instances of your GitLab instances, reducing the time it takes to clone and fetch large repositories and speeding up development.

> - Geo is part of [GitLab Premium](https://about.gitlab.com/pricing/#self-managed).
> - Introduced in GitLab Enterprise Edition 8.9.
> - We recommend you use:
>   - At least GitLab Enterprise Edition 10.0 for basic Geo features.
>   - The latest version for a better experience.
> - Make sure that all nodes run the same GitLab version.
> - Geo requires PostgreSQL 9.6 and Git 2.9, in addition to GitLab's usual [minimum requirements](../../../install/requirements.md).
> - Using Geo in combination with [High Availability](../../high_availability/README.md) is considered **Generally Available** (GA) in GitLab [GitLab Premium](https://about.gitlab.com/pricing/) 10.4.

For a video introduction to Geo, see [Introduction to GitLab Geo - GitLab Features](https://www.youtube.com/watch?v=-HDLxSjEh6w).

CAUTION: **Caution:**
Geo undergoes significant changes from release to release. Upgrades **are** supported and [documented](#updating-geo), but you should ensure that you're using the right version of the documentation for your installation.

To make sure you're using the right version of the documentation, navigate to [the source version of this page on GitLab.com](https://gitlab.com/gitlab-org/gitlab-ee/blob/master/doc/administration/geo/replication/index.md) and choose the appropriate release from the **Switch branch/tag** dropdown. For example, [`v11.2.3-ee`](https://gitlab.com/gitlab-org/gitlab-ee/blob/v11.2.3-ee/doc/administration/geo/replication/index.md).

## Use cases

Implementing Geo provides the following benefits:

- Reduce from minutes to seconds the time taken for your distributed developers to clone and fetch large repositories and projects.
- Enable all of your developers to contribute ideas and work in parallel, no matter where they are.
- Balance the load between your **primary** and **secondary** nodes, or offload your automated tests to a **secondary** node.

In addition, it:

- Can be used for cloning and fetching projects, in addition to reading any data available in the GitLab web interface (see [current limitations](#current-limitations)).
- Overcomes slow connections between distant offices, saving time by improving speed for distributed teams.
- Helps reducing the loading time for automated tasks, custom integrations, and internal workflows.
- Can quickly fail over to a **secondary** node in a [disaster recovery](../disaster_recovery/index.md) scenario.
- Allows [planned failover](../disaster_recovery/planned_failover.md) to a **secondary** node.

Geo provides:

- Read-only **secondary** nodes: Maintain one **primary** GitLab node while still enabling read-only **secondary** nodes for each of your distributed teams.
- Authentication system hooks: **Secondary** nodes receives all authentication data (like user accounts and logins) from the **primary** instance.
- An intuitive UI: **Secondary** nodes utilize the same web interface your team has grown accustomed to. In addition, there are visual notifications that block write operations and make it clear that a user is on a **secondary** node.

## How it works

Your Geo instance can be used for cloning and fetching projects, in addition to reading any data. This will make working with large repositories over large distances much faster.

![Geo overview](img/geo_overview.png)

When Geo is enabled, the:

- Original instance is known as the **primary** node.
- Replicated read-only nodes are known as **secondary** nodes.

Keep in mind that:

- **Secondary** nodes talk to the **primary** node to:
  - Get user data for logins (API).
  - Replicate repositories, LFS Objects, and Attachments (HTTPS + JWT).
- Since GitLab Premium 10.0, the **primary** node no longer talks to **secondary** nodes to notify for changes (API).
- Pushing directly to a **secondary** node (for both HTTP and SSH, including git-lfs) was [introduced](https://about.gitlab.com/2018/09/22/gitlab-11-3-released/) in [GitLab Premium](https://about.gitlab.com/pricing/#self-managed) 11.3.
- There are [limitations](#current-limitations) in the current implementation.

### Architecture

The following diagram illustrates the underlying architecture of Geo.

![Geo architecture](img/geo_architecture.png)

In this diagram:

- There is the **primary** node and the details of one **secondary** node.
- Writes to the database can only be performed on the **primary** node. A **secondary** node receives database
  updates via PostgreSQL streaming replication.
- If present, the [LDAP server](#ldap) should be configured to replicate for [Disaster Recovery](../disaster_recovery/index.md) scenarios.
- A **secondary** node performs different type of synchronizations against the **primary** node, using a special
  authorization protected by JWT:
   - Repositories are cloned/updated via Git over HTTPS.
   - Attachments, LFS objects, and other files are downloaded via HTTPS using a private API endpoint.

From the perspective of a user performing Git operations:

- The **primary** node behaves as a full read-write GitLab instance.
- **Secondary** nodes are read-only but proxy Git push operations to the **primary** node. This makes **secondary** nodes appear to support push operations themselves.

To simplify the diagram, some necessary components are omitted. Note that:

- Git over SSH requires [`gitlab-shell`](https://gitlab.com/gitlab-org/gitlab-shell) and OpenSSH.
- Git over HTTPS required [`gitlab-workhorse`](https://gitlab.com/gitlab-org/gitlab-workhorse).

Note that a **secondary** node needs two different PostgreSQL databases:

- A read-only database instance that streams data from the main GitLab database.
- [Another database instance](#geo-tracking-database) used internally by the **secondary** node to record what data has been replicated.

In **secondary** nodes, there is an additional daemon: [Geo Log Cursor](#geo-log-cursor).

## Requirements for running Geo

The following are required to run Geo:

- An operating system that supports OpenSSH 6.9+ (needed for
  [fast lookup of authorized SSH keys in the database](../../operations/fast_ssh_key_lookup.md))
  The following operating systems are known to ship with a current version of OpenSSH:
    - [CentOS](https://www.centos.org) 7.4+
    - [Ubuntu](https://www.ubuntu.com) 16.04+
- PostgreSQL 9.6+ with [FDW](https://www.postgresql.org/docs/9.6/postgres-fdw.html) support and [Streaming Replication](https://wiki.postgresql.org/wiki/Streaming_Replication)
- Git 2.9+

### Firewall rules

The following table lists basic ports that must be open between the **primary** and **secondary** nodes for Geo.

| **Primary** node | **Secondary** node | Protocol     |
|:-----------------|:-------------------|:-------------|
| 80               | 80                 | HTTP         |
| 443              | 443                | TCP or HTTPS |
| 22               | 22                 | TCP          |
| 5432             |                    | PostgreSQL   |

See the full list of ports used by GitLab in [Package defaults](https://docs.gitlab.com/omnibus/package-information/defaults.html)

NOTE: **Note:**
[Web terminal](../../../ci/environments.md#web-terminals) support requires your load balancer to correctly handle WebSocket connections.
When using HTTP or HTTPS proxying, your load balancer must be configured to pass through the `Connection` and `Upgrade` hop-by-hop headers. See the [web terminal](../../integration/terminal.md) integration guide for more details.

NOTE: **Note:**
When using HTTPS protocol for port 443, you will need to add an SSL certificate to the load balancers.
If you wish to terminate SSL at the GitLab application server instead, use TCP protocol.

### LDAP

We recommend that if you use LDAP on your **primary** node, you also set up secondary LDAP servers on each **secondary** node. Otherwise, users will not be able to perform Git operations over HTTP(s) on the **secondary** node using HTTP Basic Authentication. However, Git via SSH and personal access tokens will still work.

NOTE: **Note:**
It is possible for all **secondary** nodes to share an LDAP server, but additional latency can be an issue. Also, consider what LDAP server will be available in a [disaster recovery](../disaster_recovery/index.md) scenario if a **secondary** node is promoted to be a **primary** node.

Check for instructions on how to set up replication in your LDAP service. Instructions will be different depending on the software or service used. For example, OpenLDAP provides [these instructions](https://www.openldap.org/doc/admin24/replication.html).

### Geo Tracking Database

The tracking database instance is used as metadata to control what needs to be updated on the disk of the local instance. For example:

- Download new assets.
- Fetch new LFS Objects.
- Fetch changes from a repository that has recently been updated.

Because the replicated database instance is read-only, we need this additional database instance for each **secondary** node.
The tracking database requires the `postgres_fdw` extension.

### Geo Log Cursor

This daemon:

- Reads a log of events replicated by the **primary** node to the **secondary** database instance.
- Updates the Geo Tracking Database instance with changes that need to be executed.

When something is marked to be updated in the tracking database instance, asynchronous jobs running on the **secondary** node will execute the required operations and update the state.

This new architecture allows GitLab to be resilient to connectivity issues between the nodes. It doesn't matter how long the **secondary** node is disconnected from the **primary** node as it will be able to replay all the events in the correct order and become synchronized with the **primary** node again.

## Setup instructions

These instructions assume you have a working instance of GitLab. They guide you through:

1. Making your existing instance the **primary** node.
1. Adding **secondary** nodes.

CAUTION: **Caution:**
The steps below should be followed in the order they appear. **Make sure the GitLab version is the same on all nodes.**

### Using Omnibus GitLab

If you installed GitLab using the Omnibus packages (highly recommended):

1. [Install GitLab Enterprise Edition](https://about.gitlab.com/installation/) on the server that will serve as the **secondary** node. Do not create an account or log in to the new **secondary** node.
1. [Upload the GitLab License](https://docs.gitlab.com/ee/user/admin_area/license.html) on the **primary** node to unlock Geo. The license must be for [GitLab Premium](https://about.gitlab.com/pricing/) or higher.
1. [Set up the database replication](database.md) (`primary (read-write) <-> secondary (read-only)` topology).
1. [Configure fast lookup of authorized SSH keys in the database](../../operations/fast_ssh_key_lookup.md). This step is required and needs to be done on **both** the **primary** and **secondary** nodes.
1. [Configure GitLab](configuration.md) to set the **primary** and **secondary** nodes.
1. Optional: [Configure a secondary LDAP server](../../auth/ldap.md) for the **secondary** node. See [notes on LDAP](#ldap).
1. [Follow the "Using a Geo Server" guide](using_a_geo_server.md).

## Post-installation documentation

After installing GitLab on the **secondary** nodes and performing the initial configuration, see the following documentation for post-installation information.

### Configuring Geo

For information on configuring Geo, see [Geo configuration](configuration.md).

### Updating Geo

For information on how to update your Geo nodes to the latest GitLab version, see [Updating the Geo nodes](updating_the_geo_nodes.md).

### Configuring Geo high availability

For information on configuring Geo for high availability, see [Geo High Availability](high_availability.md).

### Configuring Geo with Object Storage

For information on configuring Geo with object storage, see [Geo with Object storage](object_storage.md).

### Disaster Recovery

For information on using Geo in disaster recovery situations to mitigate data-loss and restore services, see [Disaster Recovery](../disaster_recovery/index.md).

### Replicating the Container Registry

For more information on how to replicate the Container Registry, see [Docker Registry for a **secondary** node](docker_registry.md).

### Security Review

For more information on Geo security, see [Geo security review](security_review.md).

### Tuning Geo

For more information on tuning Geo, see [Tuning Geo](tuning.md).

## Remove Geo node

For more information on removing a Geo node, see [Removing **secondary** Geo nodes](remove_geo_node.md).

## Current limitations

CAUTION: **Caution:**
This list of limitations only reflects the latest version of GitLab. If you are using an older version, extra limitations may be in place.

- Pushing directly to a **secondary** node redirects (for HTTP) or proxies (for SSH) the request to the **primary** node instead of [handling it directly](https://gitlab.com/gitlab-org/gitlab-ee/issues/1381), except when using Git over HTTP with credentials embedded within the URI. For example, `https://user:password@secondary.tld`.
- The **primary** node has to be online for OAuth login to happen. Existing sessions and Git are not affected.
- The installation takes multiple manual steps that together can take about an hour depending on circumstances. We are working on improving this experience. See [gitlab-org/omnibus-gitlab#2978](https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2978) for details.
- Real-time updates of issues/merge requests (for example, via long polling) doesn't work on the **secondary** node.
- [Selective synchronization](configuration.md#selective-synchronization) applies only to files and repositories. Other datasets are replicated to the **secondary** node in full, making it inappropriate for use as an access control mechanism.
- Object pools for forked project deduplication work only on the **primary** node, and are duplicated on the **secondary** node.
- [External merge request diffs](../../merge_request_diffs.md) will not be replicated if they are on-disk, and viewing merge requests will fail. However, external MR diffs in object storage **are** supported. The default configuration (in-database) does work.

### Limitations on replication

Only the following items are replicated to the **secondary** node:

- All database content. For example, snippets, epics, issues, merge requests, groups, and project metadata.
- Project repositories.
- Project wiki repositories.
- User uploads. For example, attachments to issues, merge requests, epics, and avatars.
- CI job artifacts and traces.

DANGER: **DANGER**
Data not on this list is unavailable on the **secondary** node. Failing over without manually replicating data not on this list will cause the data to be **lost**.

### Examples of data not replicated

Take special note that these examples of GitLab features are both:

- Commonly used.
- **Not** replicated by Geo at present.

Examples include:

- [Elasticsearch integration](https://docs.gitlab.com/ee/integration/elasticsearch.html).
- [Container Registry](../../container_registry.md). [Object Storage](object_storage.md) can mitigate this.
- [GitLab Pages](../../pages/index.md).
- [Mattermost integration](https://docs.gitlab.com/omnibus/gitlab-mattermost/).

CAUTION: **Caution:**
If you wish to use them on a **secondary** node, or to execute a failover successfully, you will need to replicate their data using some other means.

## Frequently Asked Questions

For answers to common questions, see the [Geo FAQ](faq.md).

## Log files

Since GitLab 9.5, Geo stores structured log messages in a `geo.log` file. For Omnibus installations, this file is at `/var/log/gitlab/gitlab-rails/geo.log`.

This file contains information about when Geo attempts to sync repositories and files. Each line in the file contains a separate JSON entry that can be ingested into Elasticsearch, Splunk, etc.

For example:

```json
{"severity":"INFO","time":"2017-08-06T05:40:16.104Z","message":"Repository update","project_id":1,"source":"repository","resync_repository":true,"resync_wiki":true,"class":"Gitlab::Geo::LogCursor::Daemon","cursor_delay_s":0.038}
```

This message shows that Geo detected that a repository update was needed for project `1`.

## Troubleshooting

For troubleshooting steps, see [Geo Troubleshooting](troubleshooting.md).
