jobspec: lower min cpu resources from 10->1

Since CPU resources are usually a soft limit it is desirable to allow
setting it as low as possible to allow tasks to run only in "idle" time.

Setting it to 0 is still not allowed to avoid potential unintentional
side effects with allowing a zero value. While there may not be any side
effects this commit attempts to minimize risk by avoiding the issue.

This does *not* change the defaults.

CHANGELOG.md

@@ -4,6 +4,7 @@ IMPROVEMENTS:
  * core: Improved job deregistration error logging. [[GH-8745](https://github.com/hashicorp/nomad/issues/8745)]
  * api: Added support for cancellation contexts to HTTP API. [[GH-8836](https://github.com/hashicorp/nomad/issues/8836)]
  * driver/docker: upgrade pause container and detect architecture [[GH-8957](https://github.com/hashicorp/nomad/pull/8957)]
+ * jobspec: Lowered minimum CPU allowed from 10 to 1. [[GH-8996](https://github.com/hashicorp/nomad/issues/8996)]
 
 BUG FIXES:
 

api/resources.go

@@ -56,7 +56,7 @@ func DefaultResources() *Resources {
 // IN nomad/structs/structs.go and should be kept in sync.
 func MinResources() *Resources {
 	return &Resources{
-		CPU:      intToPtr(20),
+		CPU:      intToPtr(1),
 		MemoryMB: intToPtr(10),
 	}
 }
@@ -110,6 +110,9 @@ type NetworkResource struct {
 }
 
 func (n *NetworkResource) Canonicalize() {
+	// COMPAT(0.12) MBits is deprecated but this should not be removed
+	// until MBits is fully removed. Removing this *without* fully removing
+	// MBits would cause unnecessary job diffs and destructive updates.
 	if n.MBits == nil {
 		n.MBits = intToPtr(10)
 	}

command/agent/job_endpoint_test.go

@@ -2849,6 +2849,23 @@ func TestJobs_ApiJobToStructsJobUpdate(t *testing.T) {
 	require.Equal(t, group2, *structsJob.TaskGroups[1].Update)
 }
 
+// TestJobs_Matching_Resources asserts:
+//	api.{Default,Min}Resources == structs.{Default,Min}Resources
+//
+// While this is an odd place to test that, this is where both are imported,
+// validated, and converted.
+func TestJobs_Matching_Resources(t *testing.T) {
+	t.Parallel()
+
+	// api.MinResources == structs.MinResources
+	structsMinRes := ApiResourcesToStructs(api.MinResources())
+	assert.Equal(t, structs.MinResources(), structsMinRes)
+
+	// api.DefaultResources == structs.DefaultResources
+	structsDefaultRes := ApiResourcesToStructs(api.DefaultResources())
+	assert.Equal(t, structs.DefaultResources(), structsDefaultRes)
+}
+
 // TestHTTP_JobValidate_SystemMigrate asserts that a system job with a migrate
 // stanza fails to validate but does not panic (see #5477).
 func TestHTTP_JobValidate_SystemMigrate(t *testing.T) {

nomad/structs/structs.go

@@ -2099,7 +2099,7 @@ func DefaultResources() *Resources {
 // api/resources.go and should be kept in sync.
 func MinResources() *Resources {
 	return &Resources{
-		CPU:      20,
+		CPU:      1,
 		MemoryMB: 10,
 	}
 }
@@ -2223,11 +2223,6 @@ func (r *Resources) MeetsMinResources() error {
 	if r.MemoryMB < minResources.MemoryMB {
 		mErr.Errors = append(mErr.Errors, fmt.Errorf("minimum MemoryMB value is %d; got %d", minResources.MemoryMB, r.MemoryMB))
 	}
-	for i, n := range r.Networks {
-		if err := n.MeetsMinResources(); err != nil {
-			mErr.Errors = append(mErr.Errors, fmt.Errorf("network resource at index %d failed: %v", i, err))
-		}
-	}
 
 	return mErr.ErrorOrNil()
 }
@@ -2444,16 +2439,6 @@ func (n *NetworkResource) Canonicalize() {
 	}
 }
 
-// MeetsMinResources returns an error if the resources specified are less than
-// the minimum allowed.
-func (n *NetworkResource) MeetsMinResources() error {
-	var mErr multierror.Error
-	if n.MBits < 1 {
-		mErr.Errors = append(mErr.Errors, fmt.Errorf("minimum MBits value is 1; got %d", n.MBits))
-	}
-	return mErr.ErrorOrNil()
-}
-
 // Copy returns a deep copy of the network resource
 func (n *NetworkResource) Copy() *NetworkResource {
 	if n == nil {

nomad/structs/structs_test.go

@@ -1378,6 +1378,67 @@ func TestTask_Validate(t *testing.T) {
 	}
 }
 
+func TestTask_Validate_Resources(t *testing.T) {
+	cases := []struct {
+		name string
+		res  *Resources
+	}{
+		{
+			name: "Minimum",
+			res:  MinResources(),
+		},
+		{
+			name: "Default",
+			res:  DefaultResources(),
+		},
+		{
+			name: "Full",
+			res: &Resources{
+				CPU:      1000,
+				MemoryMB: 1000,
+				IOPS:     1000,
+				Networks: []*NetworkResource{
+					{
+						Mode:   "host",
+						Device: "localhost",
+						CIDR:   "127.0.0.0/8",
+						IP:     "127.0.0.1",
+						MBits:  1000,
+						DNS: &DNSConfig{
+							Servers:  []string{"localhost"},
+							Searches: []string{"localdomain"},
+							Options:  []string{"ndots:5"},
+						},
+						ReservedPorts: []Port{
+							{
+								Label:       "reserved",
+								Value:       1234,
+								To:          1234,
+								HostNetwork: "loopback",
+							},
+						},
+						DynamicPorts: []Port{
+							{
+								Label:       "dynamic",
+								Value:       5678,
+								To:          5678,
+								HostNetwork: "loopback",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for i := range cases {
+		tc := cases[i]
+		t.Run(tc.name, func(t *testing.T) {
+			require.NoError(t, tc.res.Validate())
+		})
+	}
+}
+
 func TestTask_Validate_Services(t *testing.T) {
 	s1 := &Service{
 		Name:      "service-name",