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: Backups
Each pods will take its own backups, and consequently have its own isolated backup / restore procedure.
1. Definition
GitLab Backup takes a backup of the PostgreSQL database used by the application, and also Git repository data.
2. Data flow
Each pod has a number of application databases to back up (e.g. main, and ci).
Additionally, there may be cluster-wide metadata tables (e.g. users table)
which is directly accesible via PostgreSQL.
3. Proposal
3.1. Cluster-wide metadata
It is currently unknown how cluster-wide metadata tables will be accessible. We may choose to have cluster-wide metadata tables backed up separately, or have each pod back up its copy of cluster-wide metdata tables.
3.2 Consistency
3.2.1 Take backups independently
As each pod will communicate with each other via API, and there will be no joins to the users table, it should be acceptable for each pod to take a backup independently of each other.
3.2.2 Enforce snapshots
We can require that each pod take a snapshot for the PostgreSQL databases at around the same time to allow for a consistent-enough backup.
4. Evaluation
As the number of pods increases, it will likely not be feasible to take a snapshot at the same time for all pods. Hence taking backups independently is the better option.