Set leave_on_terminate=true for servers and hardcode maxUnavailable=1

When leave_on_terminate=false (default), rolling the statefulset is
disruptive because the new servers come up with the same node IDs but
different IP addresses. They can't join the server cluster until the old
server's node ID is marked as failed by serf. During this time, they continually
start leader elections because they don't know there's a leader. When
they eventually join the cluster, their election term is higher, and so
they trigger a leadership swap. The leadership swap happens at the same
time as the next node to be rolled is being stopped, and so the cluster
can end up without a leader.

With leave_on_terminate=true, the stopping server cleanly leaves the
cluster, so the new server can join smoothly, even though it has the
same node ID as the old server. This increases the speed of the rollout
and in my testing eliminates the period without a leader.

The downside of this change is that when a server leaves gracefully, it
also reduces the number of raft peers. The number of peers is used to
calculate the quorum size, so this can unexpectedly change the fault
tolerance of the cluster. When running with an odd number of servers, 1
server leaving the cluster does not affect quorum size. E.g. 5 servers
=> quorum 3, 4 servers => quorum still 3. During a rollout, Kubernetes
only stops 1 server at a time, so the quorum won't change. During a
voluntary disruption event, e.g. a node being drained, Kubernetes uses
the pod disruption budget to determine how many pods in a statefulset
can be made unavailable at a time. That's why this change hardcodes this
number to 1 now.

Also set autopilot min_quorum to min quorum and disable autopilot
upgrade migration since that's for blue/green deploys.

.changelog/2962.txt

@@ -1,3 +1,3 @@
-```releast-note:feature
+```release-note:feature
 api-gateway: (Consul Enterprise) Add JWT authentication and authorization for API Gateway and HTTPRoutes.
 ```

.changelog/3000.txt

@@ -0,0 +1,36 @@
+```release-note:breaking-change
+server: set `leave_on_terminate` to `true` and set the server pod disruption budget `maxUnavailable` to `1`.
+
+This change makes server rollouts faster and more reliable. However, there is now a potential for reduced reliability if users accidentally
+scale the statefulset down. Now servers will leave the raft pool when they are stopped gracefully which reduces the fault
+tolerance. For example, with 5 servers, you can tolerate a loss of 2 servers' data as raft guarantees data is replicated to
+a majority of nodes (3). However, if you accidentally scale the statefulset down to 3, then the raft quorum will now be 2, and
+if you lose 2 servers, you may lose data. Before this change, the quorum would have remained at 3.
+
+During a regular rollout, the number of servers will be reduced by 1 at a time, which doesn't affect quorum when running
+an odd number of servers, e.g. quorum for 5 servers is 3, and quorum for 4 servers is also 3. That's why the pod disruption
+budget is being set to 1 now.
+
+If a server is stopped ungracefully, e.g. due to a node loss, it will not leave the raft pool, and so fault tolerance won't be affected.
+
+For the vast majority of users, this change will be beneficial, however if you wish to remain with the old settings you
+can set:
+
+    server:
+      extraConfig: |
+        {"leave_on_terminate": false}
+      disruptionBudget:
+        maxUnavailable: <previous setting>
+
+```
+
+```release-note:breaking-change
+server: set `autopilot.min_quorum` to the correct quorum value to ensure autopilot doesn't prune servers needed for quorum. Also set `autopilot. disable_upgrade_migration` to `true` as that setting is meant for blue/green deploys, not rolling deploys.
+
+This setting makes sense for most use-cases, however if you had a specific reason to use the old settings you can use the following config to keep them:
+
+    server:
+      extraConfig: |
+        {"autopilot": {"min_quorum": 0, "disable_upgrade_migration": false}}
+
+```

acceptance/ci-inputs/aks_acceptance_test_packages.yaml

@@ -4,4 +4,4 @@
 # Cloud package is not included in test suite as it is triggered from a non consul-k8s repo and requires HCP credentials
 - {runner: 0, test-packages: "connect peering snapshot-agent wan-federation"}
 - {runner: 1, test-packages: "consul-dns example partitions metrics sync"}
-- {runner: 2, test-packages: "basic cli config-entries api-gateway ingress-gateway terminating-gateway vault"}
+- {runner: 2, test-packages: "basic cli config-entries api-gateway ingress-gateway terminating-gateway vault server"}

acceptance/ci-inputs/eks_acceptance_test_packages.yaml

@@ -4,4 +4,4 @@
 # Cloud package is not included in test suite as it is triggered from a non consul-k8s repo and requires HCP credentials
 - {runner: 0, test-packages: "connect peering snapshot-agent wan-federation"}
 - {runner: 1, test-packages: "consul-dns example partitions metrics sync"}
-- {runner: 2, test-packages: "basic cli config-entries api-gateway ingress-gateway terminating-gateway vault"}
+- {runner: 2, test-packages: "basic cli config-entries api-gateway ingress-gateway terminating-gateway vault server"}

acceptance/ci-inputs/gke_acceptance_test_packages.yaml

@@ -4,4 +4,4 @@
 # Cloud package is not included in test suite as it is triggered from a non consul-k8s repo and requires HCP credentials
 - {runner: 0, test-packages: "connect peering snapshot-agent wan-federation"}
 - {runner: 1, test-packages: "consul-dns example partitions metrics sync"}
-- {runner: 2, test-packages: "basic cli config-entries api-gateway ingress-gateway terminating-gateway vault"}
+- {runner: 2, test-packages: "basic cli config-entries api-gateway ingress-gateway terminating-gateway vault server"}

acceptance/ci-inputs/kind_acceptance_test_packages.yaml

@@ -6,7 +6,7 @@
 - {runner: 1, test-packages: "peering"}
 - {runner: 2, test-packages: "sameness"}
 - {runner: 3, test-packages: "connect snapshot-agent wan-federation"}
-- {runner: 4, test-packages: "cli vault metrics"}
+- {runner: 4, test-packages: "cli vault metrics server"}
 - {runner: 5, test-packages: "api-gateway ingress-gateway sync example consul-dns"}
 - {runner: 6, test-packages: "config-entries terminating-gateway basic"}
 - {runner: 7, test-packages: "mesh_v2 tenancy_v2"}

acceptance/tests/example/main_test.go

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
 // Rename package to your test package.
+// NOTE: Remember to add your test package to acceptance/ci-inputs so it gets run in CI.
 package example
 
 import (

acceptance/tests/server/main_test.go

@@ -0,0 +1,18 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package server
+
+import (
+	"os"
+	"testing"
+
+	testsuite "github.com/hashicorp/consul-k8s/acceptance/framework/suite"
+)
+
+var suite testsuite.Suite
+
+func TestMain(m *testing.M) {
+	suite = testsuite.NewSuite(m)
+	os.Exit(suite.Run())
+}

acceptance/tests/server/server_test.go

@@ -0,0 +1,84 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package server
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/hashicorp/consul-k8s/acceptance/framework/consul"
+	"github.com/hashicorp/consul-k8s/acceptance/framework/helpers"
+	"github.com/hashicorp/consul-k8s/acceptance/framework/k8s"
+	"github.com/hashicorp/consul-k8s/acceptance/framework/logger"
+	"github.com/hashicorp/go-multierror"
+	"github.com/stretchr/testify/require"
+)
+
+// Test that when servers are restarted, they don't lose leadership.
+func TestServerRestart(t *testing.T) {
+	ctx := suite.Environment().DefaultContext(t)
+	replicas := 3
+	releaseName := helpers.RandomName()
+	helmValues := map[string]string{
+		"global.enabled":        "false",
+		"connectInject.enabled": "false",
+		"server.enabled":        "true",
+		"server.replicas":       fmt.Sprintf("%d", replicas),
+	}
+	consulCluster := consul.NewHelmCluster(t, helmValues, suite.Environment().DefaultContext(t), suite.Config(), releaseName)
+	consulCluster.Create(t)
+
+	// Start a separate goroutine to check if at any point more than one server is without
+	// a leader. We expect the server that is restarting to be without a leader because it hasn't
+	// yet joined the cluster but the other servers should have a leader.
+	expReadyPods := replicas - 1
+	var unmarshallErrs error
+	timesWithoutLeader := 0
+	done := make(chan bool)
+	defer close(done)
+	go func() {
+		for {
+			select {
+			case <-done:
+				return
+			default:
+				out, err := k8s.RunKubectlAndGetOutputE(t, ctx.KubectlOptions(t), "get", fmt.Sprintf("statefulset/%s-consul-server", releaseName),
+					"-o", "jsonpath={.status}")
+				if err != nil {
+					// Not failing the test on this error to reduce flakiness.
+					logger.Logf(t, "kubectl err: %s: %s", err, out)
+					break
+				}
+				type statefulsetOut struct {
+					ReadyReplicas *int `json:"readyReplicas,omitempty"`
+				}
+				var jsonOut statefulsetOut
+				if err = json.Unmarshal([]byte(out), &jsonOut); err != nil {
+					unmarshallErrs = multierror.Append(err)
+				} else if jsonOut.ReadyReplicas == nil || *jsonOut.ReadyReplicas < expReadyPods {
+					// note: for some k8s api reason when readyReplicas is 0 it's not included in the json output so
+					// that's why we're checking if it's nil.
+					timesWithoutLeader++
+				}
+				time.Sleep(1 * time.Second)
+			}
+		}
+	}()
+
+	// Restart servers
+	out, err := k8s.RunKubectlAndGetOutputE(t, ctx.KubectlOptions(t), "rollout", "restart", fmt.Sprintf("statefulset/%s-consul-server", releaseName))
+	require.NoError(t, err, out)
+
+	// Wait for restart to finish.
+	start := time.Now()
+	out, err = k8s.RunKubectlAndGetOutputE(t, ctx.KubectlOptions(t), "rollout", "status", "--timeout", "5m", "--watch", fmt.Sprintf("statefulset/%s-consul-server", releaseName))
+	require.NoError(t, err, out, "rollout status command errored, this likely means the rollout didn't complete in time")
+
+	// Check results
+	require.NoError(t, unmarshallErrs, "there were some json unmarshall errors, this is likely a bug")
+	logger.Logf(t, "restart took %s, there were %d instances where than one server had no leader", time.Since(start), timesWithoutLeader)
+	require.Equal(t, 0, timesWithoutLeader, "there were %d instances where more than one server had no leader", timesWithoutLeader)
+}

charts/consul/templates/_helpers.tpl

@@ -166,24 +166,27 @@ Expand the name of the chart.
 {{- end -}}
 
 {{/*
-Compute the maximum number of unavailable replicas for the PodDisruptionBudget.
-This defaults to (n/2)-1 where n is the number of members of the server cluster.
-Special case of replica equaling 3 and allowing a minor disruption of 1 otherwise
-use the integer value
-Add a special case for replicas=1, where it should default to 0 as well.
+Calculate max number of server pods that are allowed to be voluntarily disrupted.
+When there's 1 server, this is set to 0 because this pod should not be disrupted. This is an edge
+case and I'm not sure it makes a difference when there's only one server but that's what the previous config was and
+I don't want to change it for this edge case.
+Otherwise we've changed this to always be 1 as part of the move to set leave_on_terminate
+to true. With leave_on_terminate set to true, whenever a server pod is stopped, the number of peers in raft
+is reduced. If the number of servers is odd and the count is reduced by 1, the quorum size doesn't change,
+but if it's reduced by more than 1, the quorum size can change so that's why this is now always hardcoded to 1.
 */}}
-{{- define "consul.pdb.maxUnavailable" -}}
+{{- define "consul.server.pdb.maxUnavailable" -}}
 {{- if eq (int .Values.server.replicas) 1 -}}
 {{ 0 }}
 {{- else if .Values.server.disruptionBudget.maxUnavailable -}}
 {{ .Values.server.disruptionBudget.maxUnavailable -}}
 {{- else -}}
-{{- if eq (int .Values.server.replicas) 3 -}}
-{{- 1 -}}
-{{- else -}}
-{{- sub (div (int .Values.server.replicas) 2) 1 -}}
+{{ 1 }}
 {{- end -}}
 {{- end -}}
+
+{{- define "consul.server.autopilotMinQuorum" -}}
+{{- add (div (int .Values.server.replicas) 2) 1 -}}
 {{- end -}}
 
 {{- define "consul.pdb.connectInject.maxUnavailable" -}}

charts/consul/templates/server-config-configmap.yaml

@@ -56,7 +56,12 @@ data:
         "enabled": true
       },
       {{- end }}
-      "server": true
+      "server": true,
+      "leave_on_terminate": true,
+      "autopilot": {
+        "min_quorum": {{ template "consul.server.autopilotMinQuorum" . }},
+        "disable_upgrade_migration": true
+      }
     }
   {{- $vaultConnectCAEnabled := and .Values.global.secretsBackend.vault.connectCA.address .Values.global.secretsBackend.vault.connectCA.rootPKIPath .Values.global.secretsBackend.vault.connectCA.intermediatePKIPath -}}
   {{- if and .Values.global.secretsBackend.vault.enabled $vaultConnectCAEnabled }}

charts/consul/templates/server-disruptionbudget.yaml

@@ -17,7 +17,7 @@ metadata:
     release: {{ .Release.Name }}
     component: server
 spec:
-  maxUnavailable: {{ template "consul.pdb.maxUnavailable" . }}
+  maxUnavailable: {{ template "consul.server.pdb.maxUnavailable" . }}
   selector:
     matchLabels:
       app: {{ template "consul.name" . }}

charts/consul/test/unit/server-config-configmap.bats

@@ -1307,4 +1307,62 @@ load _helpers
       yq -r '.data["server.json"]' | jq -r .log_level | tee /dev/stderr)
 
   [ "${configmap}" = "DEBUG" ]
-}
+}
+
+#--------------------------------------------------------------------
+# server.autopilot.min_quorum
+
+@test "server/ConfigMap: autopilot.min_quorum=1 when replicas=1" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-config-configmap.yaml  \
+      --set 'server.replicas=1' \
+      . | tee /dev/stderr |
+      yq -r '.data["server.json"]' | jq -r .autopilot.min_quorum | tee /dev/stderr)
+
+  [ "${actual}" = "1" ]
+}
+
+@test "server/ConfigMap: autopilot.min_quorum=2 when replicas=2" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-config-configmap.yaml  \
+      --set 'server.replicas=2' \
+      . | tee /dev/stderr |
+      yq -r '.data["server.json"]' | jq -r .autopilot.min_quorum | tee /dev/stderr)
+
+  [ "${actual}" = "2" ]
+}
+
+@test "server/ConfigMap: autopilot.min_quorum=2 when replicas=3" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-config-configmap.yaml  \
+      --set 'server.replicas=3' \
+      . | tee /dev/stderr |
+      yq -r '.data["server.json"]' | jq -r .autopilot.min_quorum | tee /dev/stderr)
+
+  [ "${actual}" = "2" ]
+}
+
+@test "server/ConfigMap: autopilot.min_quorum=3 when replicas=4" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-config-configmap.yaml  \
+      --set 'server.replicas=4' \
+      . | tee /dev/stderr |
+      yq -r '.data["server.json"]' | jq -r .autopilot.min_quorum | tee /dev/stderr)
+
+  [ "${actual}" = "3" ]
+}
+
+@test "server/ConfigMap: autopilot.min_quorum=3 when replicas=5" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-config-configmap.yaml  \
+      --set 'server.replicas=5' \
+      . | tee /dev/stderr |
+      yq -r '.data["server.json"]' | jq -r .autopilot.min_quorum | tee /dev/stderr)
+
+  [ "${actual}" = "3" ]
+}

charts/consul/test/unit/server-disruptionbudget.bats

@@ -59,6 +59,16 @@ load _helpers
   [ "${actual}" = "0" ]
 }
 
+@test "server/DisruptionBudget: correct maxUnavailable with replicas=2" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-disruptionbudget.yaml  \
+      --set 'server.replicas=2' \
+      . | tee /dev/stderr |
+      yq '.spec.maxUnavailable' | tee /dev/stderr)
+  [ "${actual}" = "1" ]
+}
+
 @test "server/DisruptionBudget: correct maxUnavailable with replicas=3" {
   cd `chart_dir`
   local actual=$(helm template \
@@ -97,7 +107,7 @@ load _helpers
       --set 'server.replicas=6' \
       . | tee /dev/stderr |
       yq '.spec.maxUnavailable' | tee /dev/stderr)
-  [ "${actual}" = "2" ]
+  [ "${actual}" = "1" ]
 }
 
 @test "server/DisruptionBudget: correct maxUnavailable with replicas=7" {
@@ -107,7 +117,7 @@ load _helpers
       --set 'server.replicas=7' \
       . | tee /dev/stderr |
       yq '.spec.maxUnavailable' | tee /dev/stderr)
-  [ "${actual}" = "2" ]
+  [ "${actual}" = "1" ]
 }
 
 @test "server/DisruptionBudget: correct maxUnavailable with replicas=8" {
@@ -117,9 +127,21 @@ load _helpers
       --set 'server.replicas=8' \
       . | tee /dev/stderr |
       yq '.spec.maxUnavailable' | tee /dev/stderr)
-  [ "${actual}" = "3" ]
+  [ "${actual}" = "1" ]
+}
+
+@test "server/DisruptionBudget: correct maxUnavailable when set with value" {
+  cd `chart_dir`
+  local actual=$(helm template \
+      -s templates/server-disruptionbudget.yaml  \
+      --set 'server.replicas=5' \
+      --set 'server.disruptionBudget.maxUnavailable=5' \
+      . | tee /dev/stderr |
+      yq '.spec.maxUnavailable' | tee /dev/stderr)
+  [ "${actual}" = "5" ]
 }
 
+
 #--------------------------------------------------------------------
 # apiVersion
 

charts/consul/test/unit/server-statefulset.bats

@@ -792,7 +792,7 @@ load _helpers
       -s templates/server-statefulset.yaml  \
       . | tee /dev/stderr |
       yq -r '.spec.template.metadata.annotations."consul.hashicorp.com/config-checksum"' | tee /dev/stderr)
-  [ "${actual}" = 0e599137f8357c786d46e1b694d7d867c541cb34d6056241a037afd0de14866b ]
+  [ "${actual}" = 59777d0692f3bf9143a09e96e58cc95296c0eaeb7565b1c49bc932954fe4423a ]
 }
 
 @test "server/StatefulSet: adds config-checksum annotation when extraConfig is provided" {
@@ -802,7 +802,7 @@ load _helpers
       --set 'server.extraConfig="{\"hello\": \"world\"}"' \
       . | tee /dev/stderr |
       yq -r '.spec.template.metadata.annotations."consul.hashicorp.com/config-checksum"' | tee /dev/stderr)
-  [ "${actual}" = 3f54c51be3473d7ae4cb91c24ba03263b7700d9a3dc3196f624ce3c6c8e93b8f ]
+  [ "${actual}" = 326eeb3fd8f497297671791c0091e7f804727b3aaeff79a47841b65571bd4cf9 ]
 }
 
 @test "server/StatefulSet: adds config-checksum annotation when config is updated" {
@@ -812,7 +812,7 @@ load _helpers
       --set 'global.acls.manageSystemACLs=true' \
       . | tee /dev/stderr |
       yq -r '.spec.template.metadata.annotations."consul.hashicorp.com/config-checksum"' | tee /dev/stderr)
-  [ "${actual}" = b44c82c9e4732433f54eeed8a299f11de0bad82a920047c8a3ad039e512ba281 ]
+  [ "${actual}" = e14ba19e37a6b79b6fd8566597464154abe9cdc4aa7079012fb3c445ac08c526 ]
 }
 
 #--------------------------------------------------------------------