config: introduce sharding.rebalancer_mode

Closes tarantool#9657

@TarantoolBot document
Title: The `sharding.rebalancer_mode` option

The `sharding.rebalancer_mode` option can have one of three values:
`manual`, `auto` and `off`. Default value is `auto`.

If the option is set to `manual`, one of the replicasets must have the
`rebalancer` sharding role. The rebalancer will be in this replicaset.

If the option value is `auto` and there are no replicasets with the
sharding role `rebalancer`, the replicaset with rebalancer will
be selected automatically among all replicasets. If the value of the
parameter is `auto` and one of the replicasets has the sharding role
`rebalancer`, then the rebalancer will be in that replicaset.

If the option value is `off`, rebalancing will be disabled regardless of
whether a replicaset with the sharding role `rebalancer` exists or no
such replicaset exists.

changelogs/unreleased/gh-9657-option-rebalancer_mode.md

@@ -0,0 +1,3 @@
+## feature/config
+
+* Introduced the `sharding.rebalancer_mode` option (gh-9657).

src/box/lua/config/configdata.lua

@@ -217,6 +217,7 @@ function methods.sharding(self)
         'rebalancer_disbalance_threshold',
         'rebalancer_max_receiving',
         'rebalancer_max_sending',
+        'rebalancer_mode',
         'sync_timeout',
         'connection_outdate_delay',
         'failover_ping_timeout',

src/box/lua/config/instance_config.lua

@@ -1932,6 +1932,23 @@ return schema.new('instance_config', schema.record({
                 end
             end,
         }),
+        rebalancer_mode = schema.enum({
+            'manual',
+            'auto',
+            'off',
+        }, {
+            default = 'auto',
+            validate = function(data, w)
+                local scope = w.schema.computed.annotations.scope
+                if data == nil or scope == nil then
+                    return
+                end
+                if scope ~= 'global' then
+                    w.error('sharding.rebalancer_enabled must be defined in ' ..
+                            'the global scope.')
+                end
+            end,
+        }),
         rebalancer_disbalance_threshold = schema.scalar({
             type = 'number',
             default = 1,

test/config-luatest/cluster_config_schema_test.lua

@@ -298,6 +298,7 @@ g.test_defaults = function()
             rebalancer_disbalance_threshold = 1,
             rebalancer_max_receiving = 100,
             rebalancer_max_sending = 1,
+            rebalancer_mode = 'auto',
             sched_move_quota = 1,
             sched_ref_quota = 300,
             shard_index = "bucket_id",

test/config-luatest/instance_config_schema_test.lua

@@ -1590,6 +1590,7 @@ g.test_sharding = function()
             rebalancer_disbalance_threshold = 7,
             rebalancer_max_receiving = 8,
             rebalancer_max_sending = 9,
+            rebalancer_mode = 'manual',
             sched_ref_quota = 10,
             sched_move_quota = 11,
         },
@@ -1615,6 +1616,7 @@ g.test_sharding = function()
         rebalancer_disbalance_threshold = 1,
         rebalancer_max_receiving = 100,
         rebalancer_max_sending = 1,
+        rebalancer_mode = 'auto',
         sched_move_quota = 1,
         sched_ref_quota = 300,
         shard_index = "bucket_id",

test/config-luatest/vshard_test.lua

@@ -652,3 +652,55 @@ g.test_no_suitable_uri = function(g)
     local err = 'No suitable URI provided for instance "instance-001"'
     t.assert_str_contains(res.stderr, err)
 end
+
+-- Make sure that rebalancing will be disabled if rebalancer_mode == 'off', even
+-- if rebalancer sharding role is assigned.
+g.test_rebalancer_mode = function(g)
+    t.skip_if(not has_vshard, 'Module "vshard" is not available')
+    local dir = treegen.prepare_directory(g, {}, {})
+    local config = [[
+    credentials:
+      users:
+        guest:
+          roles: [super]
+        storage:
+          roles: [sharding]
+          password: "storage"
+
+    iproto:
+      listen:
+        - uri: 'unix/:./{{ instance_name }}.iproto'
+      advertise:
+        sharding:
+          login: 'storage'
+
+    sharding:
+      rebalancer_mode: off
+
+    groups:
+      group-001:
+        replicasets:
+          replicaset-001:
+            sharding:
+              roles: [storage, rebalancer, router]
+            instances:
+              instance-001: {}
+    ]]
+    local config_file = treegen.write_script(dir, 'config.yaml', config)
+    local opts = {
+        env = {LUA_PATH = os.environ()['LUA_PATH']},
+        config_file = config_file,
+        chdir = dir,
+        alias = 'instance-001',
+    }
+    g.server = server:new(opts)
+    g.server:start()
+
+    -- Check that vshard option rebalancer_mode is set to the same value.
+    local res = g.server:eval('return vshard.storage.internal.current_cfg')
+    t.assert_equals(res.rebalancer_mode, 'off')
+
+    -- Check that rebalancer is not started.
+    res = g.server:eval('return vshard.storage.internal.rebalancer_service')
+    t.assert_equals(res, nil)
+end