83 lines
3.6 KiB
Markdown
83 lines
3.6 KiB
Markdown
|
---
|
||
|
|
stage: enablement
|
||
|
|
group: pods
|
||
|
|
comments: false
|
||
|
|
description: 'Pods: Data migration'
|
||
|
|
---
|
||
|
|
|
||
|
|
DISCLAIMER:
|
||
|
|
This page may contain information related to upcoming products, features and
|
||
|
|
functionality. It is important to note that the information presented is for
|
||
|
|
informational purposes only, so please do not rely on the information for
|
||
|
|
purchasing or planning purposes. Just like with all projects, the items
|
||
|
|
mentioned on the page are subject to change or delay, and the development,
|
||
|
|
release, and timing of any products, features, or functionality remain at the
|
||
|
|
sole discretion of GitLab Inc.
|
||
|
|
|
||
|
|
This document is a work-in-progress and represents a very early state of the
|
||
|
|
Pods design. Significant aspects are not documented, though we expect to add
|
||
|
|
them in the future. This is one possible architecture for Pods, and we intend to
|
||
|
|
contrast this with alternatives before deciding which approach to implement.
|
||
|
|
This documentation will be kept even if we decide not to implement this so that
|
||
|
|
we can document the reasons for not choosing this approach.
|
||
|
|
|
||
|
|
# Pods: Data migration
|
||
|
|
|
||
|
|
It is essential for Pods architecture to provide a way to migrate data out of big Pods
|
||
|
|
into smaller ones. This describes various approaches to provide this type of split.
|
||
|
|
|
||
|
|
## 1. Definition
|
||
|
|
|
||
|
|
## 2. Data flow
|
||
|
|
|
||
|
|
## 3. Proposal
|
||
|
|
|
||
|
|
### 3.1. Split large Pods
|
||
|
|
|
||
|
|
A single Pod can only be divided into many Pods. This is based on principle
|
||
|
|
that it is easier to create exact clone of an existing Pod in many replicas
|
||
|
|
out of which some will be made authoritative once migrated. Keeping those
|
||
|
|
replicas up-to date with Pod 0 is also much easier due to pre-existing
|
||
|
|
replication solutions that can replicate the whole systems: Geo, PostgreSQL
|
||
|
|
physical replication, etc.
|
||
|
|
|
||
|
|
1. All data of an organization needs to not be divided across many Pods.
|
||
|
|
1. Split should be doable online.
|
||
|
|
1. New Pods cannot contain pre-existing data.
|
||
|
|
1. N Pods contain exact replica of Pod 0.
|
||
|
|
1. The data of Pod 0 is live replicated to as many Pods it needs to be split.
|
||
|
|
1. Once consensus is achieved between Pod 0 and N-Pods the organizations to be migrated away
|
||
|
|
are marked as read-only cluster-wide.
|
||
|
|
1. The `routes` is updated on for all organizations to be split to indicate an authorative
|
||
|
|
Pod holding the most recent data, like `gitlab-org` on `pod-100`.
|
||
|
|
1. The data for `gitlab-org` on Pod 0, and on other non-authoritative N-Pods are dormant
|
||
|
|
and will be removed in the future.
|
||
|
|
1. All accesses to `gitlab-org` on a given Pod are validated about `pod_id` of `routes`
|
||
|
|
to ensure that given Pod is authoritative to handle the data.
|
||
|
|
|
||
|
|
### 3.2. Migrate organization from an existing Pod
|
||
|
|
|
||
|
|
This is different to split, as we intend to perform logical and selective replication
|
||
|
|
of data belonging to a single organization.
|
||
|
|
|
||
|
|
Today this type of selective replication is only implemented by Gitaly where we can migrate
|
||
|
|
Git repository from a single Gitaly node to another with minimal downtime.
|
||
|
|
|
||
|
|
In this model we would require identifying all resources belonging to a given organization:
|
||
|
|
database rows, object storage files, Git repositories, etc. and selectively copy them over
|
||
|
|
to another (likely) existing Pod importing data into it. Ideally ensuring that we can
|
||
|
|
perform logical replication live of all changed data, but change similarly to split
|
||
|
|
which Pod is authoritative for this organization.
|
||
|
|
|
||
|
|
1. It is hard to identify all resources belonging to organization.
|
||
|
|
1. It requires either downtime for organization or a robust system to identify
|
||
|
|
live changes made.
|
||
|
|
1. It likely will require a full database structure analysis (more robust than project import/export)
|
||
|
|
to perform selective PostgreSQL logical replication.
|
||
|
|
|
||
|
|
## 4. Evaluation
|
||
|
|
|
||
|
|
## 4.1. Pros
|
||
|
|
|
||
|
|
## 4.2. Cons
|