Add shm_volume option (#427)

Add possibility to mount a tmpfs volume to /dev/shm to avoid issues like
[this](https://github.com/docker-library/postgres/issues/416). To achieve that
two new options were introduced:

* `enableShmVolume` to PostgreSQL manifest, to specify whether or not mount
this volume per database cluster

* `enable_shm_volume` to operator configuration, to specify whether or not mount
per operator.

The first one, `enableShmVolume` takes precedence to allow us to be more flexible.

pkg/cluster/k8sres.go

@@ -18,6 +18,7 @@ import (
 	acidv1 "github.com/zalando-incubator/postgres-operator/pkg/apis/acid.zalan.do/v1"
 	"github.com/zalando-incubator/postgres-operator/pkg/spec"
 	"github.com/zalando-incubator/postgres-operator/pkg/util"
+	"github.com/zalando-incubator/postgres-operator/pkg/util/config"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/constants"
 	"k8s.io/apimachinery/pkg/labels"
 )
@@ -396,6 +397,16 @@ func generateSidecarContainers(sidecars []acidv1.Sidecar,
 	return nil, nil
 }
 
+// Check whether or not we're requested to mount an shm volume,
+// taking into account that PostgreSQL manifest has precedence.
+func mountShmVolumeNeeded(opConfig config.Config, pgSpec *acidv1.PostgresSpec) bool {
+	if pgSpec.ShmVolume != nil {
+		return *pgSpec.ShmVolume
+	}
+
+	return opConfig.ShmVolume
+}
+
 func generatePodTemplate(
 	namespace string,
 	labels labels.Set,
@@ -407,6 +418,7 @@ func generatePodTemplate(
 	podServiceAccountName string,
 	kubeIAMRole string,
 	priorityClassName string,
+	shmVolume bool,
 ) (*v1.PodTemplateSpec, error) {
 
 	terminateGracePeriodSeconds := terminateGracePeriod
@@ -420,6 +432,10 @@ func generatePodTemplate(
 		Tolerations:                   *tolerationsSpec,
 	}
 
+	if shmVolume {
+		addShmVolume(&podSpec)
+	}
+
 	if nodeAffinity != nil {
 		podSpec.Affinity = nodeAffinity
 	}
@@ -733,7 +749,12 @@ func (c *Cluster) generateStatefulSet(spec *acidv1.PostgresSpec) (*v1beta1.State
 	volumeMounts := generateVolumeMounts()
 
 	// generate the spilo container
-	spiloContainer := generateSpiloContainer(c.containerName(), &effectiveDockerImage, resourceRequirements, spiloEnvVars, volumeMounts)
+	spiloContainer := generateSpiloContainer(c.containerName(),
+		&effectiveDockerImage,
+		resourceRequirements,
+		spiloEnvVars,
+		volumeMounts,
+	)
 
 	// resolve conflicts between operator-global and per-cluster sidecards
 	sideCars := c.mergeSidecars(spec.Sidecars)
@@ -775,7 +796,8 @@ func (c *Cluster) generateStatefulSet(spec *acidv1.PostgresSpec) (*v1beta1.State
 		int64(c.OpConfig.PodTerminateGracePeriod.Seconds()),
 		c.OpConfig.PodServiceAccountName,
 		c.OpConfig.KubeIAMRole,
-		effectivePodPriorityClassName); err != nil {
+		effectivePodPriorityClassName,
+		mountShmVolumeNeeded(c.OpConfig, spec)); err != nil {
 		return nil, fmt.Errorf("could not generate pod template: %v", err)
 	}
 
@@ -882,6 +904,32 @@ func (c *Cluster) getNumberOfInstances(spec *acidv1.PostgresSpec) int32 {
 	return newcur
 }
 
+// To avoid issues with limited /dev/shm inside docker environment, when
+// PostgreSQL can't allocate enough of dsa segments from it, we can
+// mount an extra memory volume
+//
+// see https://docs.okd.io/latest/dev_guide/shared_memory.html
+func addShmVolume(podSpec *v1.PodSpec) {
+	volumes := append(podSpec.Volumes, v1.Volume{
+		Name: constants.ShmVolumeName,
+		VolumeSource: v1.VolumeSource{
+			EmptyDir: &v1.EmptyDirVolumeSource{
+				Medium: "Memory",
+			},
+		},
+	})
+
+	pgIdx := constants.PostgresContainerIdx
+	mounts := append(podSpec.Containers[pgIdx].VolumeMounts,
+		v1.VolumeMount{
+			Name:      constants.ShmVolumeName,
+			MountPath: constants.ShmVolumePath,
+		})
+
+	podSpec.Containers[0].VolumeMounts = mounts
+	podSpec.Volumes = volumes
+}
+
 func generatePersistentVolumeClaimTemplate(volumeSize, volumeStorageClass string) (*v1.PersistentVolumeClaim, error) {
 
 	var storageClassName *string

pkg/cluster/k8sres_test.go

@@ -1,8 +1,11 @@
 package cluster
 
 import (
+	"k8s.io/api/core/v1"
+
 	acidv1 "github.com/zalando-incubator/postgres-operator/pkg/apis/acid.zalan.do/v1"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/config"
+	"github.com/zalando-incubator/postgres-operator/pkg/util/constants"
 	"github.com/zalando-incubator/postgres-operator/pkg/util/k8sutil"
 	"testing"
 )
@@ -75,3 +78,54 @@ func TestCreateLoadBalancerLogic(t *testing.T) {
 		}
 	}
 }
+
+func TestShmVolume(t *testing.T) {
+	testName := "TestShmVolume"
+	tests := []struct {
+		subTest string
+		podSpec *v1.PodSpec
+		shmPos  int
+	}{
+		{
+			subTest: "empty PodSpec",
+			podSpec: &v1.PodSpec{
+				Volumes: []v1.Volume{},
+				Containers: []v1.Container{
+					v1.Container{
+						VolumeMounts: []v1.VolumeMount{},
+					},
+				},
+			},
+			shmPos: 0,
+		},
+		{
+			subTest: "non empty PodSpec",
+			podSpec: &v1.PodSpec{
+				Volumes: []v1.Volume{v1.Volume{}},
+				Containers: []v1.Container{
+					v1.Container{
+						VolumeMounts: []v1.VolumeMount{
+							v1.VolumeMount{},
+						},
+					},
+				},
+			},
+			shmPos: 1,
+		},
+	}
+	for _, tt := range tests {
+		addShmVolume(tt.podSpec)
+
+		volumeName := tt.podSpec.Volumes[tt.shmPos].Name
+		volumeMountName := tt.podSpec.Containers[0].VolumeMounts[tt.shmPos].Name
+
+		if volumeName != constants.ShmVolumeName {
+			t.Errorf("%s %s: Expected volume %s was not created, have %s instead",
+				testName, tt.subTest, constants.ShmVolumeName, volumeName)
+		}
+		if volumeMountName != constants.ShmVolumeName {
+			t.Errorf("%s %s: Expected mount %s was not created, have %s instead",
+				testName, tt.subTest, constants.ShmVolumeName, volumeMountName)
+		}
+	}
+}