saga re-assignment should only grab sagas from Nexus of same generation

nexus/reconfigurator/execution/src/sagas.rs

@@ -9,11 +9,36 @@ use nexus_db_queries::context::OpContext;
 use nexus_db_queries::db::DataStore;
 use nexus_types::deployment::{Blueprint, BlueprintZoneDisposition};
 use omicron_common::api::external::Error;
-use omicron_uuid_kinds::GenericUuid;
+use omicron_uuid_kinds::{GenericUuid, OmicronZoneUuid};
 use slog::{debug, info, warn};
 
-/// For each expunged Nexus zone, re-assign sagas owned by that Nexus to the
-/// specified nexus (`nexus_id`).
+/// For each expunged Nexus zone in the same generation as the current Nexus,
+/// re-assign sagas owned by that Nexus to the specified nexus (`nexus_id`).
+///
+/// Reassigning sagas in this way is how we ensure that that sagas complete even
+/// when the Nexus that was running them fails permanently (leading to
+/// expungement).
+///
+/// Reassignment of sagas assigned to any expunged Nexus nodes is a prerequisite
+/// for Nexus handoff (during upgrade).  That's because in general, Nexus is
+/// tightly coupled to saga implementations and it's not safe for different
+/// versions of a Nexus to operate on the same saga (even at different times).
+/// For more on this, see RFD 289.  As a result, we finish all sagas prior to
+/// handing off from one version to the next.
+///
+/// Strictly speaking, it should not be required to limit re-assignment to Nexus
+/// instances of the same generation.  As mentioned above, sagas do not survive
+/// across generations, so the only sagas that exist ought to be from the same
+/// generation that Nexus is running.  This is a belt-and-suspenders check put
+/// in place because the impact of getting this wrong (running a saga created by
+/// an older version) could be pretty bad.
+///
+/// We could use the Nexus image for this rather than the generation.
+/// In practice, these should be equivalent here because we bump the Nexus
+/// generation on deployed systems when (and only when) there's a new Nexus
+/// image.  But handoff works in terms of generations -- that's the abstraction
+/// we've created for "a group of Nexus instances that speak the same database
+/// version and can exchange sagas".  So that's what we use here.
 pub(crate) async fn reassign_sagas_from_expunged(
     opctx: &OpContext,
     datastore: &DataStore,
@@ -22,29 +47,12 @@ pub(crate) async fn reassign_sagas_from_expunged(
 ) -> Result<bool, Error> {
     let log = &opctx.log;
 
-    // Identify any Nexus zones that have been expunged and need to have sagas
-    // re-assigned.
-    //
-    // TODO: Currently, we take any expunged Nexus instances and attempt to
-    // assign all their sagas to ourselves.  Per RFD 289, we can only re-assign
-    // sagas between two instances of Nexus that are at the same version.  Right
-    // now this can't happen so there's nothing to do here to ensure that
-    // constraint.  However, once we support allowing the control plane to be
-    // online _during_ an upgrade, there may be multiple different Nexus
-    // instances running at the same time.  At that point, we will need to make
-    // sure that we only ever try to assign ourselves sagas from other Nexus
-    // instances that we know are running the same version as ourselves.
-    let nexus_zone_ids: Vec<_> = blueprint
-        .all_omicron_zones(BlueprintZoneDisposition::is_ready_for_cleanup)
-        .filter_map(|(_, z)| {
-            z.zone_type
-                .is_nexus()
-                .then(|| nexus_db_model::SecId(z.id.into_untyped_uuid()))
-        })
-        .collect();
-
-    debug!(log, "re-assign sagas: found Nexus instances";
-        "nexus_zone_ids" => ?nexus_zone_ids);
+    let nexus_zone_ids = find_expunged_same_generation(blueprint, nexus_id)?;
+    debug!(
+        log,
+        "re-assign sagas: found expunged Nexus instances with matching generation";
+        "nexus_zone_ids" => ?nexus_zone_ids
+    );
 
     let result =
         datastore.sagas_reassign_sec(opctx, &nexus_zone_ids, nexus_id).await;
@@ -68,3 +76,203 @@ pub(crate) async fn reassign_sagas_from_expunged(
         }
     }
 }
+
+/// Returns the list of Nexus ids for expunged (and ready-to-cleanup) Nexus
+/// zones in the same generation as the given Nexus id
+fn find_expunged_same_generation(
+    blueprint: &Blueprint,
+    nexus_id: SecId,
+) -> Result<Vec<SecId>, Error> {
+    let nexus_zone_id = OmicronZoneUuid::from_untyped_uuid(nexus_id.0);
+    let active_nexus_generation =
+        blueprint.find_generation_for_self(nexus_zone_id)?;
+    Ok(blueprint
+        .all_nexus_zones(BlueprintZoneDisposition::is_ready_for_cleanup)
+        .filter_map(|(_sled_id, zone_config, nexus_config)| {
+            (nexus_config.nexus_generation == active_nexus_generation)
+                .then_some(zone_config.id)
+        })
+        .map(|id| SecId(id.into_untyped_uuid()))
+        .collect())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use nexus_reconfigurator_planning::blueprint_builder::BlueprintBuilder;
+    use nexus_reconfigurator_planning::example::ExampleSystemBuilder;
+    use nexus_reconfigurator_planning::planner::PlannerRng;
+    use nexus_types::deployment::BlueprintSource;
+    use omicron_common::api::external::Generation;
+    use omicron_test_utils::dev::test_setup_log;
+    use std::collections::BTreeSet;
+    use uuid::Uuid;
+
+    #[test]
+    fn test_find_expunged_same_generation() {
+        const TEST_NAME: &str = "test_find_expunged_same_generation";
+
+        let logctx = test_setup_log(TEST_NAME);
+        let log = &logctx.log;
+
+        // To do an exhaustive test of `find_expunged_same_generation()`, we
+        // want some expunged zones and some non-expunged zones in each of two
+        // different generations.
+
+        // Frst, create a basic blueprint with several Nexus zones in generation 1.
+        let (example, blueprint1) =
+            ExampleSystemBuilder::new(log, TEST_NAME).nexus_count(4).build();
+        let g1 = Generation::new();
+        let g1_nexus_ids: Vec<_> = blueprint1
+            .all_nexus_zones(BlueprintZoneDisposition::is_in_service)
+            .map(|(sled_id, zone_config, nexus_config)| {
+                assert_eq!(nexus_config.nexus_generation, g1);
+                (sled_id, zone_config.id, zone_config.image_source.clone())
+            })
+            .collect();
+
+        // Expunge two of these Nexus zones and mark them ready for cleanup
+        // immediately.
+        let (g1_expunge_ids, g1_keep_ids) = g1_nexus_ids.split_at(2);
+        let mut builder = BlueprintBuilder::new_based_on(
+            log,
+            &blueprint1,
+            &example.input,
+            &example.collection,
+            "test suite",
+            PlannerRng::from_entropy(),
+        )
+        .expect("new blueprint builder");
+
+        for (sled_id, expunge_id, _image_source) in g1_expunge_ids {
+            builder
+                .sled_expunge_zone(*sled_id, *expunge_id)
+                .expect("expunge zone");
+            builder
+                .sled_mark_expunged_zone_ready_for_cleanup(
+                    *sled_id,
+                    *expunge_id,
+                )
+                .expect("mark zone for cleanup");
+        }
+
+        // Create the same number of Nexus zones in the next generation.
+        // We'll use the same images.
+        let g2 = g1.next();
+        for (sled_id, _zone_id, image_source) in &g1_nexus_ids {
+            builder
+                .sled_add_zone_nexus(*sled_id, image_source.clone(), g2)
+                .expect("add Nexus zone");
+        }
+
+        let blueprint2 = builder.build(BlueprintSource::Test);
+        let g2_nexus_ids: Vec<_> = blueprint2
+            .all_nexus_zones(BlueprintZoneDisposition::is_in_service)
+            .filter_map(|(sled_id, zone_config, nexus_config)| {
+                (nexus_config.nexus_generation == g2)
+                    .then_some((sled_id, zone_config.id))
+            })
+            .collect();
+
+        // Now expunge a few of those, too.  This time, only the first is going
+        // to be marked ready for cleanup.
+        let (g2_expunge_ids, g2_keep_ids) = g2_nexus_ids.split_at(2);
+        let mut builder = BlueprintBuilder::new_based_on(
+            log,
+            &blueprint2,
+            &example.input,
+            &example.collection,
+            "test suite",
+            PlannerRng::from_entropy(),
+        )
+        .expect("new blueprint builder");
+
+        let (sled_id, g2_expunged_cleaned_up) = g2_expunge_ids[0];
+        builder
+            .sled_expunge_zone(sled_id, g2_expunged_cleaned_up)
+            .expect("expunge zone");
+        builder
+            .sled_mark_expunged_zone_ready_for_cleanup(
+                g2_expunge_ids[0].0,
+                g2_expunged_cleaned_up,
+            )
+            .expect("mark zone for cleanup");
+
+        let (sled_id, g2_expunged_not_cleaned_up) = g2_expunge_ids[1];
+        builder
+            .sled_expunge_zone(sled_id, g2_expunged_not_cleaned_up)
+            .expect("expunge zone");
+
+        let blueprint3 = builder.build(BlueprintSource::Test);
+
+        // Finally, we have:
+        //
+        // - g1_keep_ids:    two in-service Nexus zones in generation 1
+        // - g1_expunge_ids: two expunged Nexus zones in generation 1,
+        //                   both cleaned up
+        // - g2_keep_ids:    two in-service Nexus zones in generation 2
+        // - g2_expunge_ids: expunged Nexus zones in generation 2,
+        //                   only the first of which is ready for cleanup
+        //
+        // Now we can exhaustively test various cases.
+
+        // For the in-service zones in generation 1, we should find the expunged
+        // zones in generation 1.
+        let g1_matched: BTreeSet<SecId> = g1_expunge_ids
+            .into_iter()
+            .map(|(_sled_id, zone_id, _image_source)| {
+                SecId(zone_id.into_untyped_uuid())
+            })
+            .collect();
+        for (_sled_id, zone_id, _image_source) in g1_keep_ids {
+            let matched = find_expunged_same_generation(
+                &blueprint3,
+                SecId(zone_id.into_untyped_uuid()),
+            )
+            .unwrap();
+            assert_eq!(
+                matched.into_iter().collect::<BTreeSet<_>>(),
+                g1_matched
+            );
+        }
+
+        // It should be impossible in a real system for the
+        // expunged-and-ready-to-cleanup zones to execute this function.  Being
+        // ready to cleanup means we know they're gone.  So there's nothing to
+        // test here.
+
+        // For the in-service zones in generation 2, we should find the
+        // expunged-and-ready-for-cleanup zone in generation 2.
+        let g2_matched = SecId(g2_expunged_cleaned_up.into_untyped_uuid());
+        for (_sled_id, zone_id) in g2_keep_ids {
+            let matched = find_expunged_same_generation(
+                &blueprint3,
+                SecId(zone_id.into_untyped_uuid()),
+            )
+            .unwrap();
+            assert_eq!(matched.len(), 1);
+            assert_eq!(matched[0], g2_matched);
+        }
+
+        // It is possible for the expunged and not-yet-ready-for-cleanup zone in
+        // generation 2 to wind up calling this function.  It should not find
+        // itself!
+        let matched = find_expunged_same_generation(
+            &blueprint3,
+            SecId(g2_expunged_not_cleaned_up.into_untyped_uuid()),
+        )
+        .unwrap();
+        assert_eq!(matched.len(), 1);
+        assert_eq!(matched[0], g2_matched);
+
+        // Test the sole error case: if we cannot figure out which generation we
+        // were given.
+        let error =
+            find_expunged_same_generation(&blueprint3, SecId(Uuid::new_v4()))
+                .expect_err("made-up Nexus should not exist");
+        assert!(matches!(error, Error::InternalError { internal_message }
+            if internal_message.contains("did not find Nexus")));
+
+        logctx.cleanup_successful();
+    }
+}

nexus/types/src/deployment.rs

@@ -479,7 +479,7 @@ impl Blueprint {
         nexus_id: OmicronZoneUuid,
     ) -> Result<Generation, Error> {
         for (_sled_id, zone_config, nexus_config) in
-            self.all_nexus_zones(BlueprintZoneDisposition::is_in_service)
+            self.all_nexus_zones(BlueprintZoneDisposition::could_be_running)
         {
             if zone_config.id == nexus_id {
                 return Ok(nexus_config.nexus_generation);