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Physalia

Definition

Physalia is EBS's configuration / control-plane subsystem. Public reference: "Millions of Tiny Databases" (USENIX NSDI 2020) by Brooker et al. In the 2024 Marc Olson retrospective it appears only as a whiteboard photo with the caption "Removing the control plane from the IO path with Physalia" — i.e., Physalia is the mechanism by which the EBS data plane no longer has to consult a centralized control plane in the hot IO path.

This is a canonical instance of concepts/control-plane-data-plane-separation: rollout decisions, topology changes, and lease management are handled by a dedicated control plane off the IO path, so that data-plane outages and control-plane outages are independent.

Seen in

• sources/2024-08-22-allthingsdistributed-continuous-reinvention-block-storage-at-aws — named/illustrated as the control-plane-off-the-IO-path change.

External references

• Brooker, Mitchell, et al., "Millions of Tiny Databases," NSDI 2020 — the Physalia paper.