[I] ClusterRouterPool AdjustPoolSize can bypass cluster deployment constraints [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin opened a new issue, #3362:
URL: https://github.com/apache/pekko/issues/3362

   ### Summary
   
   `AdjustPoolSize` sent to a `ClusterRouterPool` can create a local routee without applying the cluster pool's deployment constraints. In particular, it can create a local child when `allowLocalRoutees` is `false`. The same inherited path also does not consult `useRoles`, `totalInstances`, or `maxInstancesPerNode`.
   
   ### Reproducer
   
   On current `main` (`1fa250d450e18bbebd0374378b6e2a8069473e46`), this directional test in `ClusterRouterSupervisorSpec` exposes the issue:
   
   ```scala
   import pekko.routing.{ AdjustPoolSize, GetRoutees, Routees, RoundRobinPool }
   
   "not create a local routee through AdjustPoolSize when local routees are disabled" in {
     val router = system.actorOf(
       ClusterRouterPool(
         RoundRobinPool(nrOfInstances = 0),
         ClusterRouterPoolSettings(
           totalInstances = 1,
           maxInstancesPerNode = 1,
           allowLocalRoutees = false))
         .props(Props(classOf[KillableActor])))
   
     router ! AdjustPoolSize(1)
     router ! GetRoutees
   
     expectMsg(Routees(Vector.empty))
   }
   ```
   
   Run with JDK 17:
   
   ```text
   sbt "cluster / Test / testOnly org.apache.pekko.cluster.routing.ClusterRouterSupervisorSpec"
   ```
   
   The assertion fails because a local routee named `c1` is present:
   
   ```text
   expected Routees(Vector()), found Routees(Vector(ActorRefRoutee(Actor[pekko://.../c1])))
   ```
   
   ### Cause
   
   `ClusterRouterPoolActor` inherits `RouterPoolActor` and delegates unmatched messages, including `AdjustPoolSize`, to `super.receive`:
   
   - https://github.com/apache/pekko/blob/1fa250d450e18bbebd0374378b6e2a8069473e46/cluster/src/main/scala/org/apache/pekko/cluster/routing/ClusterRouterConfig.scala#L403-L409
   
   The inherited handler calls `pool.newRoutee` directly for each requested addition:
   
   - https://github.com/apache/pekko/blob/1fa250d450e18bbebd0374378b6e2a8069473e46/actor/src/main/scala/org/apache/pekko/routing/RoutedActorCell.scala#L203-L214
   
   For a `ClusterRouterPool`, `newRoutee` attaches a local child without checking cluster settings:
   
   - https://github.com/apache/pekko/blob/1fa250d450e18bbebd0374378b6e2a8069473e46/cluster/src/main/scala/org/apache/pekko/cluster/routing/ClusterRouterConfig.scala#L342-L360
   
   In contrast, the normal cluster-pool allocation path calls `selectDeploymentTarget`, which applies available-node, total-instance, and per-node limits:
   
   - https://github.com/apache/pekko/blob/1fa250d450e18bbebd0374378b6e2a8069473e46/cluster/src/main/scala/org/apache/pekko/cluster/routing/ClusterRouterConfig.scala#L411-L450
   
   The documentation also states that `max-nr-of-instances-per-node` will not be exceeded:
   
   - https://github.com/apache/pekko/blob/1fa250d450e18bbebd0374378b6e2a8069473e46/docs/src/main/paradox/cluster-routing.md#L171-L177
   
   ### Expected behavior
   
   `AdjustPoolSize` must not create a routee on a node excluded by `allowLocalRoutees` or `useRoles`, and must not silently bypass cluster pool limits.
   
   The exact management semantics need a maintainer decision. Possible approaches include rejecting/ignoring `AdjustPoolSize` for cluster pools, or interpreting it through the cluster allocation path while preserving `totalInstances` and `maxInstancesPerNode`.
   
   ### Additional context
   
   This was found while investigating #3253. It is separate from the generic pool/resizer-bounds question there: the generic `AdjustPoolSize` contract is a direct management override, whereas cluster deployment settings describe node eligibility and per-node limits.
   


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Re: [I] ClusterRouterPool AdjustPoolSize can bypass cluster deployment constraints [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin closed issue #3362: ClusterRouterPool AdjustPoolSize can bypass cluster deployment constraints
URL: https://github.com/apache/pekko/issues/3362


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