config: add isolated option on the instance level

This commit just adds the option into the cluster configuration schema.
Next commits will add the relevant logic.

Part of tarantool#10796

NO_DOC=tarantool/doc#4632

Author: Totktonada

changelogs/unreleased/config-isolated-instance.md

@@ -0,0 +1,3 @@
+## feature/config
+
+* Add `isolated` option for instances (gh-10796).

src/box/lua/config/instance_config.lua

@@ -455,6 +455,37 @@ local function feedback_validate(data, w)
     w.error('Tarantool is built without feedback reports sending support')
 end
 
+-- Verify that the given validation context (w) corresponds to the
+-- instance level of the cluster configuration or the validation
+-- is performed against the instance config schema.
+local function validate_scope_is_instance(w)
+    local scope = w.schema.computed.annotations.scope
+
+    -- scope = nil means that the validation is performed against
+    -- the instance config schema, not the cluster config.
+    --
+    -- The validation against the instance config is performed for
+    -- values from the env configuration source (which collects
+    -- the TT_* environment variables).
+    --
+    -- Also, it would be very counter-intuitive if
+    -- cluster_config:instantiate() would produce a result that
+    -- doesn't pass the instance_config:validate() check.
+    if scope == nil then
+        return
+    end
+
+    -- scope = 'instance' means that the option is placed on the
+    -- instance level of the cluster configuration.
+    if scope == 'instance' then
+        return
+    end
+
+    -- Any other level of the cluster configuration (replicaset,
+    -- group, global) scope -- raise an error.
+    w.error('The option must not be present in the %s scope', scope)
+end
+
 return schema.new('instance_config', schema.record({
     config = schema.record({
         reload = schema.enum({
@@ -2475,6 +2506,13 @@ return schema.new('instance_config', schema.record({
             type = 'string',
         }),
     }),
+    isolated = schema.scalar({
+        type = 'boolean',
+        default = false,
+        validate = function(_data, w)
+            validate_scope_is_instance(w)
+        end,
+    }),
 }, {
     -- This kind of validation cannot be implemented as the
     -- 'validate' annotation of a particular schema node. There

test/config-luatest/cluster_config_schema_test.lua

@@ -1,6 +1,7 @@
 local yaml = require('yaml')
 local fio = require('fio')
 local t = require('luatest')
+local instance_config = require('internal.config.instance_config')
 local cluster_config = require('internal.config.cluster_config')
 
 local g = t.group()
@@ -92,6 +93,7 @@ local instance_config_fields = {
     'failover',
     'compat',
     'labels',
+    'isolated',
 }
 
 -- Verify that the fields of the given schema correspond to the
@@ -427,6 +429,7 @@ g.test_defaults = function()
             console_session_scope_vars = 'old',
             wal_cleanup_delay_deprecation = 'old',
         },
+        isolated = false,
     }
 
     -- Global defaults.
@@ -739,3 +742,66 @@ g.test_additional_options_instance = function()
         .fields.instances.value
     verify_fields(schema, {})
 end
+
+-- Attempt to pass the `isolated` option to different cluster
+-- configuration levels and also try to validate it against the
+-- instance config.
+--
+-- The option should be accepted only by the instance config or
+-- the instance level of the cluster config.
+g.test_isolated_scope = function()
+    local function exp_err(path, scope)
+        return ('[cluster_config] %s: The option must not be present in the ' ..
+            '%s scope'):format(path, scope)
+    end
+
+    local data = {isolated = true}
+
+    -- Global level: forbidden.
+    local path = 'isolated'
+    t.assert_error_msg_equals(exp_err(path, 'global'), function()
+        cluster_config:validate(data)
+    end)
+
+    -- Group level: forbidden.
+    local path = 'groups.g.isolated'
+    t.assert_error_msg_equals(exp_err(path, 'group'), function()
+        cluster_config:validate({
+            groups = {
+                g = data,
+            },
+        })
+    end)
+
+    -- Replicaset level: forbidden.
+    local path = 'groups.g.replicasets.r.isolated'
+    t.assert_error_msg_equals(exp_err(path, 'replicaset'), function()
+        cluster_config:validate({
+            groups = {
+                g = {
+                    replicasets = {
+                        r = data,
+                    },
+                },
+            },
+        })
+    end)
+
+    -- Instance level: accepted.
+    cluster_config:validate({
+        groups = {
+            g = {
+                replicasets = {
+                    r = {
+                        instances = {
+                            i = data,
+                        },
+                    },
+                },
+            },
+        },
+    })
+
+    -- Validation against the instance config: accepted.
+    instance_config:validate(data)
+end

test/config-luatest/instance_config_schema_test.lua

@@ -1764,3 +1764,8 @@ g.test_labels = function()
 
     t.assert_equals(instance_config:apply_default({}).labels, nil)
 end
+
+g.test_isolated = function()
+    instance_config:validate({isolated = true})
+    t.assert_equals(instance_config:apply_default({}).isolated, false)
+end