Persistent Volumes

What are Persistent Volumes?

Persistent Volumes are a Kubernetes feature that allows you to attach stateful storage (like an EBS volume) to Pods (i.e., your PaaSTA instance).

Caveats

In general, we discourage the use of Persistent Volumes in favor of totally stateless services (i.e., where the state is separated from the service itself in a DB, S3, etc.)

That said, there are several things to keep in mind before deciding to use Persistent Volumes:

PaaSTA does not provide monitoring for Persistent Volumes - you are responsible for staying on top of your usage (i.e., there is no alerting for full or almost full volumes)
Persistent Volumes cannot be resized online - if you run out of space and need to expand your volume: there will be downtime
- Additionally, PaaSTA cannot automatically handle this resize: you will need to find an engineer on the Compute Infrastructure team to do this
If you need to delete the Persistent Volume for your service for whatever reason, you will need an engineer on the Compute Infrastructure team to do this for you
As of this writing (2024-02-16), we’ve occasionally noticed some large (double-digit minute) delays where Kubernetes is unable to attach the EBS volume backing a Persistent Volume because of AWS errors.
- In other words, until the cause of this issue is identified, it’s possible that a Spot interruption (or other sort of disruption) could potentially cause downtime for your service

How do I use Persistent Volumes in PaaSTA?

If the above is acceptable, adding a block like:

persistent_volumes:
- container_path: /path/to/mount
  # if you're a power-user, know what you're doing, and need something more specific than a bog-standard GP3 EBS volume - come talk to use in #paasta
  storage_class_name: ebs-retain-gp3
  size: 10 # in GB
  mode: RW  # unless you're populating the EBS volume externally, you likely want to be able to write to the volume :)

to your instance config will attach a Persistent Volume with 10GB of storage to every replica of your PaaSTA instance at /path/to/mount.

NOTE: a Persistent Volume will be created per-replica - they are not shared between replicas.