[nexus] move UuidRng code out to a common crate, make CollectionBuilder use it (#5341)

In #5270, we need determinism not just from blueprints but also
collections. So move the UuidRng into a common place.

As part of that, I also decided to make it its own crate and write some
documentation about it, making it more generic along the way. I think
this should be a pretty clean representation of what this is trying to do.

Author: sunshowers

Cargo.lock

@@ -70,6 +70,7 @@ members = [
     "test-utils",
     "tufaceous-lib",
     "tufaceous",
+    "typed-rng",
     "update-common",
     "update-engine",
     "uuid-kinds",
@@ -149,6 +150,7 @@ default-members = [
     "test-utils",
     "tufaceous-lib",
     "tufaceous",
+    "typed-rng",
     "update-common",
     "update-engine",
     "uuid-kinds",
@@ -343,6 +345,7 @@ propolis-mock-server = { git = "https://github.com/oxidecomputer/propolis", rev
 proptest = "1.4.0"
 quote = "1.0"
 rand = "0.8.5"
+rand_core = "0.6.4"
 rand_seeder = "0.2.3"
 ratatui = "0.26.1"
 rayon = "1.9"
@@ -434,6 +437,7 @@ trybuild = "1.0.89"
 tufaceous = { path = "tufaceous" }
 tufaceous-lib = { path = "tufaceous-lib" }
 tui-tree-widget = "0.17.0"
+typed-rng = { path = "typed-rng" }
 unicode-width = "0.1.11"
 update-common = { path = "update-common" }
 update-engine = { path = "update-engine" }

Cargo.toml

@@ -19,6 +19,7 @@ sled-agent-client.workspace = true
 slog.workspace = true
 strum.workspace = true
 thiserror.workspace = true
+typed-rng.workspace = true
 uuid.workspace = true
 omicron-workspace-hack.workspace = true
 

nexus/inventory/Cargo.toml

@@ -29,8 +29,10 @@ use nexus_types::inventory::SledAgent;
 use nexus_types::inventory::Zpool;
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
+use std::hash::Hash;
 use std::sync::Arc;
 use thiserror::Error;
+use typed_rng::UuidRng;
 use uuid::Uuid;
 
 /// Describes an operational error encountered during the collection process
@@ -86,6 +88,8 @@ pub struct CollectionBuilder {
         BTreeMap<RotPageWhich, BTreeMap<Arc<BaseboardId>, RotPageFound>>,
     sleds: BTreeMap<Uuid, SledAgent>,
     omicron_zones: BTreeMap<Uuid, OmicronZonesFound>,
+    // We just generate one UUID for each collection.
+    id_rng: UuidRng,
 }
 
 impl CollectionBuilder {
@@ -111,6 +115,7 @@ impl CollectionBuilder {
             rot_pages_found: BTreeMap::new(),
             sleds: BTreeMap::new(),
             omicron_zones: BTreeMap::new(),
+            id_rng: UuidRng::from_entropy(),
         }
     }
 
@@ -123,7 +128,7 @@ impl CollectionBuilder {
         }
 
         Collection {
-            id: Uuid::new_v4(),
+            id: self.id_rng.next(),
             errors: self.errors.into_iter().map(|e| e.to_string()).collect(),
             time_started: self.time_started,
             time_done: now_db_precision(),
@@ -140,6 +145,18 @@ impl CollectionBuilder {
         }
     }
 
+    /// Within tests, set a seeded RNG for deterministic results.
+    ///
+    /// This will ensure that tests that use this builder will produce the same
+    /// results each time they are run.
+    pub fn set_rng_seed<H: Hash>(&mut self, seed: H) -> &mut Self {
+        // Important to add some more bytes here, so that builders with the
+        // same seed but different purposes don't end up with the same UUIDs.
+        const SEED_EXTRA: &str = "collection-builder";
+        self.id_rng.set_seed(seed, SEED_EXTRA);
+        self
+    }
+
     /// Record service processor state `sp_state` reported by MGS
     ///
     /// `sp_type` and `slot` identify which SP this was.

nexus/inventory/src/builder.rs

@@ -16,10 +16,10 @@ nexus-inventory.workspace = true
 nexus-types.workspace = true
 omicron-common.workspace = true
 rand.workspace = true
-rand_seeder.workspace = true
 sled-agent-client.workspace = true
 slog.workspace = true
 thiserror.workspace = true
+typed-rng.workspace = true
 uuid.workspace = true
 
 omicron-workspace-hack.workspace = true

nexus/reconfigurator/planning/Cargo.toml

@@ -38,7 +38,6 @@ use omicron_common::api::external::Vni;
 use omicron_common::api::internal::shared::NetworkInterface;
 use omicron_common::api::internal::shared::NetworkInterfaceKind;
 use rand::rngs::StdRng;
-use rand::RngCore;
 use rand::SeedableRng;
 use slog::o;
 use slog::Logger;
@@ -50,6 +49,7 @@ use std::net::Ipv4Addr;
 use std::net::Ipv6Addr;
 use std::net::SocketAddrV6;
 use thiserror::Error;
+use typed_rng::UuidRng;
 use uuid::Uuid;
 
 /// Errors encountered while assembling blueprints
@@ -223,7 +223,7 @@ impl<'a> BlueprintBuilder<'a> {
             })
             .collect::<Result<_, Error>>()?;
         Ok(Blueprint {
-            id: rng.blueprint_rng.next_uuid(),
+            id: rng.blueprint_rng.next(),
             blueprint_zones,
             parent_blueprint_id: None,
             internal_dns_version,
@@ -375,7 +375,7 @@ impl<'a> BlueprintBuilder<'a> {
         let blueprint_zones =
             self.zones.into_zones_map(self.policy.sleds.keys().copied());
         Blueprint {
-            id: self.rng.blueprint_rng.next_uuid(),
+            id: self.rng.blueprint_rng.next(),
             blueprint_zones,
             parent_blueprint_id: Some(self.parent_blueprint.id),
             internal_dns_version: self.internal_dns_version,
@@ -452,7 +452,7 @@ impl<'a> BlueprintBuilder<'a> {
             .collect();
 
         let zone = OmicronZoneConfig {
-            id: self.rng.zone_rng.next_uuid(),
+            id: self.rng.zone_rng.next(),
             underlay_address: ip,
             zone_type: OmicronZoneType::InternalNtp {
                 address: ntp_address.to_string(),
@@ -502,7 +502,7 @@ impl<'a> BlueprintBuilder<'a> {
         let port = omicron_common::address::CRUCIBLE_PORT;
         let address = SocketAddrV6::new(ip, port, 0, 0).to_string();
         let zone = OmicronZoneConfig {
-            id: self.rng.zone_rng.next_uuid(),
+            id: self.rng.zone_rng.next(),
             underlay_address: ip,
             zone_type: OmicronZoneType::Crucible {
                 address,
@@ -589,7 +589,7 @@ impl<'a> BlueprintBuilder<'a> {
         };
 
         for _ in 0..num_nexus_to_add {
-            let nexus_id = self.rng.zone_rng.next_uuid();
+            let nexus_id = self.rng.zone_rng.next();
             let external_ip = self
                 .available_external_ips
                 .next()
@@ -617,7 +617,7 @@ impl<'a> BlueprintBuilder<'a> {
                     .next()
                     .ok_or(Error::NoSystemMacAddressAvailable)?;
                 NetworkInterface {
-                    id: self.rng.network_interface_rng.next_uuid(),
+                    id: self.rng.network_interface_rng.next(),
                     kind: NetworkInterfaceKind::Service { id: nexus_id },
                     name: format!("nexus-{nexus_id}").parse().unwrap(),
                     ip,
@@ -739,14 +739,14 @@ struct BlueprintBuilderRng {
 
 impl BlueprintBuilderRng {
     fn new() -> Self {
-        Self::new_from_rng(StdRng::from_entropy())
+        Self::new_from_parent(StdRng::from_entropy())
     }
 
-    fn new_from_rng(mut root_rng: StdRng) -> Self {
-        let blueprint_rng = UuidRng::from_root_rng(&mut root_rng, "blueprint");
-        let zone_rng = UuidRng::from_root_rng(&mut root_rng, "zone");
+    fn new_from_parent(mut parent: StdRng) -> Self {
+        let blueprint_rng = UuidRng::from_parent_rng(&mut parent, "blueprint");
+        let zone_rng = UuidRng::from_parent_rng(&mut parent, "zone");
         let network_interface_rng =
-            UuidRng::from_root_rng(&mut root_rng, "network_interface");
+            UuidRng::from_parent_rng(&mut parent, "network_interface");
 
         BlueprintBuilderRng { blueprint_rng, zone_rng, network_interface_rng }
     }
@@ -755,40 +755,7 @@ impl BlueprintBuilderRng {
         // Important to add some more bytes here, so that builders with the
         // same seed but different purposes don't end up with the same UUIDs.
         const SEED_EXTRA: &str = "blueprint-builder";
-        let mut seeder = rand_seeder::Seeder::from((seed, SEED_EXTRA));
-        *self = Self::new_from_rng(seeder.make_rng::<StdRng>());
-    }
-}
-
-#[derive(Debug)]
-pub(crate) struct UuidRng {
-    rng: StdRng,
-}
-
-impl UuidRng {
-    /// Returns a new `UuidRng` generated from the root RNG.
-    ///
-    /// `extra` is a string that should be unique to the purpose of the UUIDs.
-    fn from_root_rng(root_rng: &mut StdRng, extra: &'static str) -> Self {
-        let seed = root_rng.next_u64();
-        let mut seeder = rand_seeder::Seeder::from((seed, extra));
-        Self { rng: seeder.make_rng::<StdRng>() }
-    }
-
-    /// `extra` is a string that should be unique to the purpose of the UUIDs.
-    pub(crate) fn from_seed<H: Hash>(seed: H, extra: &'static str) -> Self {
-        let mut seeder = rand_seeder::Seeder::from((seed, extra));
-        Self { rng: seeder.make_rng::<StdRng>() }
-    }
-
-    /// Returns a new UUIDv4 generated from the RNG.
-    pub(crate) fn next_uuid(&mut self) -> Uuid {
-        let mut bytes = [0; 16];
-        self.rng.fill_bytes(&mut bytes);
-        // Builder::from_random_bytes will turn the random bytes into a valid
-        // UUIDv4. (Parts of the system depend on the UUID actually being valid
-        // v4, so it's important that we don't just use `uuid::from_bytes`.)
-        uuid::Builder::from_random_bytes(bytes).into_uuid()
+        *self = Self::new_from_parent(typed_rng::from_seed(seed, SEED_EXTRA));
     }
 }
 
@@ -1013,7 +980,7 @@ pub mod test {
         assert_eq!(diff.sleds_changed().count(), 0);
 
         // The next step is adding these zones to a new sled.
-        let new_sled_id = example.sled_rng.next_uuid();
+        let new_sled_id = example.sled_rng.next();
         let _ =
             example.system.sled(SledBuilder::new().id(new_sled_id)).unwrap();
         let policy = example.system.to_policy().unwrap();

nexus/reconfigurator/planning/src/blueprint_builder.rs

@@ -5,7 +5,6 @@
 //! Example blueprints
 
 use crate::blueprint_builder::BlueprintBuilder;
-use crate::blueprint_builder::UuidRng;
 use crate::system::SledBuilder;
 use crate::system::SystemDescription;
 use nexus_types::deployment::Blueprint;
@@ -14,6 +13,7 @@ use nexus_types::deployment::Policy;
 use nexus_types::inventory::Collection;
 use omicron_common::api::external::Generation;
 use sled_agent_client::types::OmicronZonesConfig;
+use typed_rng::UuidRng;
 
 pub struct ExampleSystem {
     pub system: SystemDescription,
@@ -38,8 +38,7 @@ impl ExampleSystem {
     ) -> ExampleSystem {
         let mut system = SystemDescription::new();
         let mut sled_rng = UuidRng::from_seed(test_name, "ExampleSystem");
-        let sled_ids: Vec<_> =
-            (0..nsleds).map(|_| sled_rng.next_uuid()).collect();
+        let sled_ids: Vec<_> = (0..nsleds).map(|_| sled_rng.next()).collect();
         for sled_id in &sled_ids {
             let _ = system.sled(SledBuilder::new().id(*sled_id)).unwrap();
         }
@@ -107,6 +106,7 @@ impl ExampleSystem {
         let blueprint = builder.build();
         let mut builder =
             system.to_collection_builder().expect("failed to build collection");
+        builder.set_rng_seed((test_name, "ExampleSystem collection"));
 
         for sled_id in blueprint.sleds() {
             let Some(zones) = blueprint.blueprint_zones.get(&sled_id) else {

nexus/reconfigurator/planning/src/example.rs

@@ -402,7 +402,7 @@ mod test {
         verify_blueprint(&blueprint2);
 
         // Now add a new sled.
-        let new_sled_id = example.sled_rng.next_uuid();
+        let new_sled_id = example.sled_rng.next();
         let _ =
             example.system.sled(SledBuilder::new().id(new_sled_id)).unwrap();
         let policy = example.system.to_policy().unwrap();

nexus/reconfigurator/planning/src/planner.rs

@@ -0,0 +1,11 @@
+[package]
+name = "typed-rng"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+omicron-workspace-hack.workspace = true
+rand.workspace = true
+rand_core.workspace = true
+rand_seeder.workspace = true
+uuid.workspace = true