---
stage: Enablement
group: Geo
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
type: howto
---

# Geo Frequently Asked Questions **(PREMIUM SELF)**

## What are the minimum requirements to run Geo?

The requirements are listed [on the index page](../index.md#requirements-for-running-geo)

## How does Geo know which projects to sync?

On each **secondary** site, there is a read-only replicated copy of the GitLab database.
A **secondary** site also has a tracking database where it stores which projects have been synced.
Geo compares the two databases to find projects that are not yet tracked.

At the start, this tracking database is empty, so Geo tries to update from every project that it can see in the GitLab database.

For each project to sync:

1. Geo issues a `git fetch geo --mirror` to get the latest information from the **primary** site.
   If there are no changes, the sync is fast. Otherwise, it has to pull the latest commits.
1. The **secondary** site updates the tracking database to store the fact that it has synced projects A, B, C, and so on.
1. Repeat until all projects are synced.

When someone pushes a commit to the **primary** site, it generates an event in the GitLab database that the repository has changed.
The **secondary** site sees this event, marks the project in question as dirty, and schedules the project to be resynced.

To ensure that problems with pipelines (for example, syncs failing too many times or jobs being lost) don't permanently stop projects syncing, Geo also periodically checks the tracking database for projects that are marked as dirty. This check happens when
the number of concurrent syncs falls below `repos_max_capacity` and there are no new projects waiting to be synced.

Geo also has a checksum feature which runs a SHA256 sum across all the Git references to the SHA values.
If the refs don't match between the **primary** site and the **secondary** site, then the **secondary** site will mark that project as dirty and try to resync it.
So even if we have an outdated tracking database, the validation should activate and find discrepancies in the repository state and resync.

## Can I use Geo in a disaster recovery situation?

Yes, but there are limitations to what we replicate (see
[What data is replicated to a **secondary** site?](#what-data-is-replicated-to-a-secondary-site)).

Read the documentation for [Disaster Recovery](../disaster_recovery/index.md).

## What data is replicated to a **secondary** site?

We currently replicate project repositories, LFS objects, generated
attachments and avatars, and the whole database. This means user accounts,
issues, merge requests, groups, project data, and so on, will be available for
query.

## Can I `git push` to a **secondary** site?

Yes! Pushing directly to a **secondary** site (for both HTTP and SSH, including Git LFS) was [introduced](https://about.gitlab.com/releases/2018/09/22/gitlab-11-3-released/) in GitLab 11.3.

## How long does it take to have a commit replicated to a **secondary** site?

All replication operations are asynchronous and are queued to be dispatched. Therefore, it depends on a lot of
factors including the amount of traffic, how big your commit is, the
connectivity between your sites, your hardware, and so on.

## What if the SSH server runs at a different port?

That's totally fine. We use HTTP(s) to fetch repository changes from the **primary** site to all **secondary** sites.

## Is this possible to set up a Docker Registry for a **secondary** site that mirrors the one on the **primary** site?

Yes. See [Docker Registry for a **secondary** site](docker_registry.md).

## Can I login to a secondary site?

Yes, but secondary sites receive all authentication data (like user accounts and logins) from the primary instance. This means you are re-directed to the primary for authentication and then routed back.
