Don't allow setting dead server last contact threshold to less than 1 minute

changelog/22040.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+storage/raft: Cap the minimum dead_server_last_contact_threshold to 1m.
+```

vault/external_tests/raft/raft_autopilot_test.go

@@ -194,6 +194,14 @@ func TestRaft_Autopilot_Configuration(t *testing.T) {
 	writeConfigFunc(writableConfig, true)
 	configCheckFunc(config)
 
+	// Check dead server last contact threshold minimum
+	writableConfig = map[string]interface{}{
+		"cleanup_dead_servers":               true,
+		"dead_server_last_contact_threshold": "5s",
+	}
+	writeConfigFunc(writableConfig, true)
+	configCheckFunc(config)
+
 	// Ensure that the configuration stays across reboots
 	leaderCore := cluster.Cores[0]
 	testhelpers.EnsureCoreSealed(t, cluster.Cores[0])
@@ -450,7 +458,7 @@ func TestRaft_Autopilot_DeadServerCleanup(t *testing.T) {
 	// Ensure Autopilot has the aggressive settings
 	config.CleanupDeadServers = true
 	config.ServerStabilizationTime = 5 * time.Second
-	config.DeadServerLastContactThreshold = 10 * time.Second
+	config.DeadServerLastContactThreshold = 1 * time.Minute
 	config.MaxTrailingLogs = 10
 	config.LastContactThreshold = 10 * time.Second
 	config.MinQuorum = 3

vault/logical_system_raft.go

@@ -533,6 +533,10 @@ func (b *SystemBackend) handleStorageRaftAutopilotConfigUpdate() framework.Opera
 			return logical.ErrorResponse(fmt.Sprintf("min_quorum must be set when cleanup_dead_servers is set and it should at least be 3; cleanup_dead_servers: %#v, min_quorum: %#v", effectiveConf.CleanupDeadServers, effectiveConf.MinQuorum)), logical.ErrInvalidRequest
 		}
 
+		if effectiveConf.CleanupDeadServers && effectiveConf.DeadServerLastContactThreshold.Seconds() < 60 {
+			return logical.ErrorResponse(fmt.Sprintf("dead_server_last_contact_threshold should not be set to less than 1m; received: %v", deadServerLastContactThreshold)), logical.ErrInvalidRequest
+		}
+
 		// Persist only the user supplied fields
 		if persist {
 			entry, err := logical.StorageEntryJSON(raftAutopilotConfigurationStoragePath, config)

website/content/api-docs/system/storage/raftautopilot.mdx

@@ -210,7 +210,8 @@ This endpoint is used to modify the configuration of the autopilot subsystem of
 
 - `dead_server_last_contact_threshold` `(string: "24h")` - Limit on the amount of time
   a server can go without leader contact before being considered failed. This
-  takes effect only when `cleanup_dead_servers` is `true`.
+  takes effect only when `cleanup_dead_servers` is `true`. This can not be set to a value
+  smaller than 1m.
 
 - `max_trailing_logs` `(int: 1000)` - Amount of entries in the Raft Log that a server
   can be behind before being considered unhealthy.