Unable to scale down task groups independently in nomad

[sijo13]

Hi,

We are using an open-source version of Nomad. Nomad version is v1.9.3

There is an issue where we are unable to scale down task groups in a job independently.

When a task group is scaled down or up, it causes the task beloging to another group of same job to restart.

Reproduction steps

In the below job specification, we have 2 task groups, nginx-group1 and nginx-group2.

job "nginx" {
  namespace = "platforms"
  node_pool = "platforms"
  group "nginx-group1" {
    count = 1
    network {
      port "http" {
        to = "80"
      }
    }
    task "nginx-task" {
     driver = "docker"
     config {
        image = "nginx:latest"
        ports = ["http"]

    }

      service {
        name     = "platforms-nginx-service"
        port     = "http"
        provider = "consul"

        check {
          type     = "http"
          port     = "http"
          path     = "/"
          interval = "2s"
          timeout  = "2s"
        }
      }
    }
  }
  group "nginx-group2" {
    count = 1
    network {
      port "http" {
        to = "80"
      }
    }
    task "nginx-task" {
     driver = "docker"
     config {
        image = "nginx:latest"
        ports = ["http"]

    }

      service {
        name     = "platforms-nginx-service"
        port     = "http"
        provider = "consul"

        check {
          type     = "http"
          port     = "http"
          path     = "/"
          interval = "2s"
          timeout  = "2s"
        }
      }
    }
  }
}

scaling down nginx-group1 to 0.
nomad_job % nomad job scale nginx nginx-group1 0

sijo.george@macblr0263 nomad_job % nomad job scale nginx nginx-group1 0
==> 2025-01-25T14:10:59+05:30: Monitoring evaluation "648b5bb9"
    2025-01-25T14:10:59+05:30: Evaluation triggered by job "nginx"
    2025-01-25T14:10:59+05:30: Allocation "fb80a82b" modified: node "86c82a4a", group "nginx-group2"
    2025-01-25T14:11:00+05:30: Evaluation within deployment: "2538df26"
    2025-01-25T14:11:00+05:30: Evaluation status changed: "pending" -> "complete"
==> 2025-01-25T14:11:00+05:30: Evaluation "648b5bb9" finished with status "complete"
==> 2025-01-25T14:11:00+05:30: Monitoring deployment "2538df26"
  ✓ Deployment "2538df26" successful

    2025-01-25T14:11:12+05:30
    ID          = 2538df26
    Job ID      = nginx
    Job Version = 3
    Status      = successful
    Description = Deployment completed successfully

    Deployed
    Task Group    Desired  Placed  Healthy  Unhealthy  Progress Deadline
    nginx-group2  1        1       1        0          2025-01-25T14:21:09+05:30

This will result in restart the allocation belonging to nginx-group2

sijo.george@macblr0263 nomad_job % nomad job status nginx
ID            = nginx
Name          = nginx
Submit Date   = 2025-01-25T14:10:59+05:30
Type          = service
Priority      = 50
Datacenters   = *
Namespace     = platforms
Node Pool     = platforms
Status        = running
Periodic      = false
Parameterized = false

Summary
Task Group    Queued  Starting  Running  Failed  Complete  Lost  Unknown
nginx-group1  0       0         0        0       2         0     0
nginx-group2  0       0         1        0       0         0     0

Latest Deployment
ID          = 2538df26
Status      = successful
Description = Deployment completed successfully

Deployed
Task Group    Desired  Placed  Healthy  Unhealthy  Progress Deadline
nginx-group2  1        1       1        0          2025-01-25T14:21:09+05:30

Allocations
ID        Node ID   Task Group    Version  Desired  Status    Created     Modified
9b31b80a  86c82a4a  nginx-group1  2        stop     complete  14m13s ago  2m13s ago
e8687ec7  86c82a4a  nginx-group1  0        stop     complete  15m18s ago  14m36s ago
fb80a82b  86c82a4a  nginx-group2  3        run      running   15m18s ago  2m2s ago`

Expected Result

Nomad task groups should scale up and down independently