[ip-pools] Allow multiple default IP pools per silo

Previously, each silo could only have one default IP pool. This change
allows one default pool per (pool_type, ip_version) combination, enabling
silos to have separate defaults for:
  - Unicast IPv4
  - Unicast IPv6
  - Multicast IPv4
  - Multicast IPv6

Now, each default can be set or unset and demoted independently.
Unsetting the unicast IPv4 default does not affect the multicast IPv4
default, for example.

Key changes:
  - Add `pool_type` and `ip_version` columns to `ip_pool_resource`
    (denormalized from parent `ip_pool` for unique index)
  - Replace unique index with partial index on (resource_id, pool_type,
    ip_version) WHERE is_default = true
  - Rename `IpPoolResourceLink` to `IncompleteIpPoolResource` to reflect
    that pool_type/ip_version are populated by the linking query

Author: zeeshanlakhani

nexus/db-model/src/ip_pool.rs

@@ -289,13 +289,32 @@ impl std::fmt::Display for IpPoolType {
     }
 }
 
+/// IP pool resource type.
+///
+/// `pool_type` and `ip_version` are denormalized from [IpPool]
+/// for a unique index on defaults.
 #[derive(Queryable, Insertable, Selectable, Clone, Copy, Debug, PartialEq)]
 #[diesel(table_name = ip_pool_resource)]
 pub struct IpPoolResource {
     pub ip_pool_id: Uuid,
     pub resource_type: IpPoolResourceType,
     pub resource_id: Uuid,
     pub is_default: bool,
+    pub pool_type: IpPoolType,
+    pub ip_version: IpVersion,
+}
+
+/// Input for creating an IP pool resource.
+///
+/// The `pool_type` and `ip_version` fields are populated from [IpPool]
+/// by the `link_ip_pool_to_external_silo_query` query, so they are not needed
+/// as input.
+#[derive(Clone, Copy, Debug)]
+pub struct IncompleteIpPoolResource {
+    pub ip_pool_id: Uuid,
+    pub resource_type: IpPoolResourceType,
+    pub resource_id: Uuid,
+    pub is_default: bool,
 }
 
 impl From<IpPoolResource> for views::IpPoolSiloLink {

nexus/db-model/src/schema_versions.rs

@@ -16,7 +16,7 @@ use std::{collections::BTreeMap, sync::LazyLock};
 ///
 /// This must be updated when you change the database schema.  Refer to
 /// schema/crdb/README.adoc in the root of this repository for details.
-pub const SCHEMA_VERSION: Version = Version::new(213, 0, 0);
+pub const SCHEMA_VERSION: Version = Version::new(214, 0, 0);
 
 /// List of all past database schema versions, in *reverse* order
 ///
@@ -28,6 +28,7 @@ static KNOWN_VERSIONS: LazyLock<Vec<KnownVersion>> = LazyLock::new(|| {
         // |  leaving the first copy as an example for the next person.
         // v
         // KnownVersion::new(next_int, "unique-dirname-with-the-sql-files"),
+        KnownVersion::new(214, "multiple-default-ip-pools-per-silo"),
         KnownVersion::new(213, "multicast-drop-mvlan"),
         KnownVersion::new(212, "multicast-member-ip-and-indexes"),
         KnownVersion::new(211, "blueprint-sled-config-subnet"),