## Problem
In order to build AZ aware scheduling, the storage controller needs to
know what AZ pageservers are in.
Related https://github.com/neondatabase/neon/issues/8848
## Summary of changes
This patch set adds a new nullable column to the `nodes` table:
`availability_zone_id`. The node registration
request is extended to include the AZ id (pageservers already have this
in their `metadata.json` file).
If the node is already registered, then we update the persistent and
in-memory state with the provided AZ.
Otherwise, we add the node with the AZ to begin with.
A couple assumptions are made here:
1. Pageserver AZ ids are stable
2. AZ ids do not change over time
Once all pageservers have a configured AZ, we can remove the optionals
in the code and make the database column not nullable.
## Problem
Storage controller restarts cause temporary unavailability from the
control plane POV. See RFC for more details.
## Summary of changes
* A couple of small refactors of the storage controller start-up
sequence to make extending it easier.
* A leader table is added to track the storage controller instance
that's currently the leader (if any)
* A peer client is added such that storage controllers can send
`step_down` requests to each other (implemented in
https://github.com/neondatabase/neon/pull/8512).
* Implement the leader cut-over as described in the RFC
* Add `start-as-candidate` flag to the storage controller to gate the
rolling restart behaviour. When the flag is `false` (the default), the
only change from the current start-up sequence is persisting the leader
entry to the database.
Part of #8128, followed by #8502.
## Problem
Currently we lack mechanism to alert unhealthy `scan_metadata` status if
we start running this scrubber command as part of a cronjob. With the
storage controller client introduced to storage scrubber in #8196, it is
viable to set up alert by storing health status in the storage
controller database.
We intentionally do not store the full output to the database as the
json blobs potentially makes the table really huge. Instead, only a
health status and a timestamp recording the last time metadata health
status is posted on a tenant shard.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
The binary etc were renamed some time ago, but the path in the source
tree remained "attachment_service" to avoid disruption to ongoing PRs.
There aren't any big PRs out right now, so it's a good time to cut over.
- Rename `attachment_service` to `storage_controller`
- Move it to the top level for symmetry with `storage_broker` & to avoid
mixing the non-prod neon_local stuff (`control_plane/`) with the storage
controller which is a production component.
