config: introduce roles

This patch introduces initial support for roles. Dependencies are not
currently supported for roles. In this regard, there is no strict order
in which roles are performed.

Part of tarantool#9078

@TarantoolBot document
Title: Roles

Roles are programs that run when a configuration is loaded or reloaded.
Roles can be defined for each instance. On first run, the role is
initialized with the init() method. On each run, the role calls
validate_config() and then apply_config() if validate_config() returns
true. If the roles were removed from the instance on reboot, the role is
stopped using the stop() method.

If a role was added to an instance, then removed from the instance, and
then added again, init() will be called.

If a role is defined more than once on an instance, it will still only
run once.

Roles must have four methods: init(), validate_config(), apply_config()
and stop().

changelogs/unreleased/gh-9078-roles.md

@@ -0,0 +1,4 @@
+## feature/config
+
+* Introduced the initial support for roles - programs that run when
+  a configuration is loaded or reloaded (gh-9078).

src/box/CMakeLists.txt

@@ -44,6 +44,7 @@ lua_source(lua_sources lua/config/applier/console.lua     config_applier_console
 lua_source(lua_sources lua/config/applier/credentials.lua config_applier_credentials_lua)
 lua_source(lua_sources lua/config/applier/fiber.lua       config_applier_fiber_lua)
 lua_source(lua_sources lua/config/applier/mkdir.lua       config_applier_mkdir_lua)
+lua_source(lua_sources lua/config/applier/roles.lua       config_applier_roles_lua)
 lua_source(lua_sources lua/config/applier/sharding.lua    config_applier_sharding_lua)
 lua_source(lua_sources lua/config/cluster_config.lua      config_cluster_config_lua)
 lua_source(lua_sources lua/config/configdata.lua          config_configdata_lua)

src/box/lua/config/applier/roles.lua

@@ -0,0 +1,62 @@
+local log = require('internal.config.utils.log')
+
+local last_loaded = {}
+
+local function stop_roles(roles)
+    for role_name, role in pairs(last_loaded) do
+        if roles == nil or not roles[role_name] then
+            log.verbose('roles.post_apply: stop role ' .. role_name)
+            role.stop()
+        end
+    end
+end
+
+local function apply(config)
+    local configdata = config._configdata
+    local role_names = configdata:get('roles', {use_default = true})
+    if role_names == nil or next(role_names) == nil then
+        stop_roles()
+        return
+    end
+
+    -- Remove duplicates.
+    local roles = {}
+    for _, role_name in pairs(role_names) do
+        roles[role_name] = true
+    end
+
+    -- Run roles.
+    local roles_cfg = configdata:get('roles_cfg', {use_default = true}) or {}
+    local loaded = {}
+    for role_name in pairs(roles) do
+        local role = last_loaded[role_name]
+        if not role then
+            role = require(role_name)
+            local methods = {'init', 'validate_config', 'apply_config', 'stop'}
+            for _, method_name in pairs(methods) do
+                if type(role[method_name]) ~= 'function' then
+                    local err = 'Role %s does not contain method %s'
+                    error(err:format(role_name, method_name), 0)
+                end
+            end
+            log.verbose('roles.post_apply: initialize role ' .. role_name)
+            role.init()
+        end
+        loaded[role_name] = role
+        local role_cfg = roles_cfg[role_name]
+        if not role.validate_config(role_cfg) then
+            error('Wrong config for role ' .. role_name, 0)
+        end
+        log.verbose('roles.post_apply: apply config for role ' .. role_name)
+        role.apply_config(role_cfg)
+    end
+
+    -- Stop removed roles.
+    stop_roles(roles)
+    last_loaded = loaded
+end
+
+return {
+    name = 'roles',
+    apply = apply,
+}

src/box/lua/config/init.lua

@@ -150,6 +150,7 @@ function methods._initialize(self)
     self:_register_applier(require('internal.config.applier.console'))
     self:_register_applier(require('internal.config.applier.fiber'))
     self:_register_applier(require('internal.config.applier.sharding'))
+    self:_register_applier(require('internal.config.applier.roles'))
     self:_register_applier(require('internal.config.applier.app'))
 
     if extras ~= nil then

src/box/lua/config/instance_config.lua

@@ -1802,6 +1802,13 @@ return schema.new('instance_config', schema.record({
             "compatibility",
         }),
     })),
+    roles_cfg = schema.map({
+        key = schema.scalar({type = 'string'}),
+        value = schema.scalar({type = 'any'}),
+    }),
+    roles = schema.array({
+        items = schema.scalar({type = 'string'})
+    }),
 }, {
     -- This kind of validation cannot be implemented as the
     -- 'validate' annotation of a particular schema node. There

src/box/lua/init.c

@@ -144,6 +144,7 @@ extern char session_lua[],
 	config_applier_credentials_lua[],
 	config_applier_fiber_lua[],
 	config_applier_mkdir_lua[],
+	config_applier_roles_lua[],
 	config_applier_sharding_lua[],
 	config_cluster_config_lua[],
 	config_configdata_lua[],
@@ -387,6 +388,10 @@ static const char *lua_sources[] = {
 	"internal.config.applier.sharding",
 	config_applier_sharding_lua,
 
+	"config/applier/roles",
+	"internal.config.applier.roles",
+	config_applier_roles_lua,
+
 	"config/init",
 	"config",
 	config_init_lua,

test/config-luatest/helpers.lua

@@ -88,13 +88,20 @@ local simple_config = {
 
 local function prepare_case(g, opts)
     local dir = opts.dir
+    local roles = opts.roles
     local script = opts.script
     local options = opts.options
 
     if dir == nil then
         dir = treegen.prepare_directory(g, {}, {})
     end
 
+    if roles ~= nil and next(roles) ~= nil then
+        for name, body in pairs(roles) do
+            treegen.write_script(dir, name .. '.lua', body)
+        end
+    end
+
     if script ~= nil then
         treegen.write_script(dir, 'main.lua', script)
     end
@@ -135,6 +142,10 @@ end
 -- Start a server with the given script and the given
 -- configuration, run a verification function on it.
 --
+-- * opts.roles
+--
+--   Role codes for writing into corresponding files.
+--
 -- * opts.script
 --
 --   Code write into the main.lua file.
@@ -164,6 +175,7 @@ end
 -- Start tarantool process with the given script/config and check
 -- the error.
 --
+-- * opts.roles
 -- * opts.script
 -- * opts.options
 --
@@ -185,12 +197,17 @@ end
 -- Start a server, write a new script/config, reload, run a
 -- verification function.
 --
+-- * opts.roles
 -- * opts.script
 -- * opts.options
 -- * opts.verify
 --
 --   Same as in success_case().
 --
+-- * opts.roles_2
+--
+--   A new list of roles to prepare before config:reload().
+--
 -- * opts.script_2
 --
 --   A new script to write into the main.lua file before
@@ -205,6 +222,7 @@ end
 --
 --   Verify test invariants after config:reload().
 local function reload_success_case(g, opts)
+    local roles_2 = opts.roles_2
     local script_2 = opts.script_2
     local options = assert(opts.options)
     local verify_2 = assert(opts.verify_2)
@@ -214,6 +232,7 @@ local function reload_success_case(g, opts)
 
     prepare_case(g, {
         dir = prepared.dir,
+        roles = roles_2,
         script = script_2,
         options = options_2,
     })
@@ -227,31 +246,44 @@ end
 -- Start a server, write a new script/config, reload, run a
 -- verification function.
 --
+-- * opts.roles
 -- * opts.script
 -- * opts.options
 -- * opts.verify
 --
 --   Same as in success_case().
 --
+-- * opts.roles_2
+--
+--   A new list of roles to prepare before config:reload().
+--
 -- * opts.script_2
 --
 --   A new script to write into the main.lua file before
 --   config:reload().
 --
+-- * opts.options_2
+--
+--   A new config to use for the config:reload(). It is optional,
+--   if not provided opts.options is used instead.
+--
 -- * opts.exp_err
 --
 --   An error that config:reload() must raise.
 local function reload_failure_case(g, opts)
-    local script_2 = assert(opts.script_2)
+    local script_2 = opts.script_2
+    local roles_2 = opts.roles_2
     local options = assert(opts.options)
+    local options_2 = opts.options_2 or options
     local exp_err = assert(opts.exp_err)
 
     local prepared = success_case(g, opts)
 
     prepare_case(g, {
         dir = prepared.dir,
+        roles = roles_2,
         script = script_2,
-        options = options,
+        options = options_2,
     })
     t.assert_error_msg_equals(exp_err, g.server.exec, g.server, function()
         local config = require('config')