[#1840] neofs-node: Allow to use mode: disabled in config

Currently, when removing shard special care must be taken with respect
to shard numbering. `mode: disabled` allows to leave shard configuration
in place while also ignoring it during initialization. This makes
disk replacement much more convenient.

Signed-off-by: Evgenii Stratonikov <evgeniy@morphbits.ru>

CHANGELOG.md

@@ -16,6 +16,7 @@ Changelog for NeoFS Node
 - Validate policy before container creation (#1704)
 - `--timeout` flag in `neofs-cli` subcommands (#1837)
 - `container nodes` command to output list of nodes for container, grouped by replica (#1704)
+- Configuration flag to ignore shard in `neofs-node` (#1840)
 
 ### Changed
 - Allow to evacuate shard data with `EvacuateShard` control RPC (#1800)
@@ -56,6 +57,10 @@ When issuing an object session token for root (virtual, "big") objects,
 additionally include all members of the split-chain. If session context
 includes root object only, it is not spread to physical ("small") objects.
 
+`neofs-node` configuration now supports `mode: disabled` flag for a shard.
+This can be used to temporarily ignore shards without completely removing them
+from the config file.
+
 ## [0.32.0] - 2022-09-14 - Pungdo (풍도, 楓島)
 
 ### Added

cmd/neofs-node/config/engine/config.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/nspcc-dev/neofs-node/cmd/neofs-node/config"
 	shardconfig "github.com/nspcc-dev/neofs-node/cmd/neofs-node/config/engine/shard"
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/shard/mode"
 )
 
 const (
@@ -31,6 +32,7 @@ func IterateShards(c *config.Config, required bool, f func(*shardconfig.Config)
 	c = c.Sub("shard")
 	def := c.Sub("default")
 
+	alive := 0
 	i := uint64(0)
 	for ; ; i++ {
 		si := strconv.FormatUint(i, 10)
@@ -48,11 +50,16 @@ func IterateShards(c *config.Config, required bool, f func(*shardconfig.Config)
 		}
 		(*config.Config)(sc).SetDefault(def)
 
+		if sc.Mode() == mode.Disabled {
+			continue
+		}
+
 		if err := f(sc); err != nil {
 			return err
 		}
+		alive++
 	}
-	if i == 0 && required {
+	if alive == 0 && required {
 		return ErrNoShardConfigured
 	}
 	return nil

cmd/neofs-node/config/engine/shard/config.go

@@ -128,6 +128,8 @@ func (x *Config) Mode() (m mode.Mode) {
 		m = mode.Degraded
 	case "degraded-read-only":
 		m = mode.DegradedReadOnly
+	case "disabled":
+		m = mode.Disabled
 	default:
 		panic(fmt.Sprintf("unknown shard mode: %s", s))
 	}

pkg/local_object_storage/shard/mode/mode.go

@@ -1,5 +1,7 @@
 package mode
 
+import "math"
+
 // Mode represents enumeration of Shard work modes.
 type Mode uint32
 
@@ -12,6 +14,11 @@ const (
 	// after a certain number of errors is encountered. It is the same as
 	// `mode.Degraded` but also is read-only.
 	DegradedReadOnly = Degraded | ReadOnly
+
+	// Disabled mode is a mode where a shard is disabled.
+	// An existing shard can't have this mode, but it can be used in
+	// the configuration or control service commands.
+	Disabled = math.MaxUint32
 )
 
 const (
@@ -36,6 +43,8 @@ func (m Mode) String() string {
 		return "DEGRADED_READ_WRITE"
 	case DegradedReadOnly:
 		return "DEGRADED_READ_ONLY"
+	case Disabled:
+		return "DISABLED"
 	}
 }