Add new param to forbid adding new members

membership.lua

@@ -37,6 +37,7 @@ local _sync_trigger = stash.get('_sync_trigger') or fiber.cond()
 local _ack_trigger = stash.get('_ack_trigger') or fiber.cond()
 local _ack_cache = stash.get('_ack_cache') or {}
 local _resolve_cache = stash.get('_resolve_cache') or {}
+local _global_params = stash.get('global_params')
 
 local function after_reload()
     stash.set('_ack_cache', _ack_cache)
@@ -484,7 +485,8 @@ local function _protocol_step()
             end
             -- calculate time difference between local time and member time
             local delta = _get_clock_delta(ack_data)
-            members.set(uri, member.status, member.incarnation, { clock_delta = delta }) -- update timstamp
+            members.set(uri, member.status, member.incarnation, { clock_delta = delta },
+                { forbid_new = _global_params.forbid_new_members }) -- update timstamp
             return
         end
     end
@@ -519,7 +521,8 @@ local function _protocol_step()
         end
         -- calculate time difference between local time and member time
         local delta = _get_clock_delta(ack_data)
-        members.set(uri, member.status, member.incarnation, { clock_delta = delta })
+        members.set(uri, member.status, member.incarnation, { clock_delta = delta },
+            { forbid_new = _global_params.forbid_new_members })
         return
     elseif members.get(uri).status == opts.ALIVE then
         local myself = members.get(advertise_uri)
@@ -601,12 +604,22 @@ end
 --   either hostname or IP address being advertised to other members
 -- @tparam number port
 --   UDP port to bind and advertise
+-- @tparam table opts Available options:
+--
+-- @tparam ?boolean opts.forbid_new_members
+--   Forbids to add new members to the group. New members could be added
+--   only with `probe_uri`.
 -- @treturn boolean `true`
 -- @raise Socket bind error
-local function init(advertise_host, port)
-    checks('string', 'number')
+local function init(advertise_host, port, params)
+    checks('string', 'number', { forbid_new_members = '?boolean' })
 
     local parts = uri_tools.parse(advertise_host)
+
+    if params and params.forbid_new_members ~= nil then
+        _global_params.forbid_new_members = params.forbid_new_members
+    end
+
     if _sock == nil or _sock:name().port ~= port then
         local family = parts.ipv6 and 'AF_INET6' or 'AF_INET'
         local addr = parts.ipv6 and '::' or '0.0.0.0'
@@ -924,8 +937,8 @@ end
 -- @treturn ?string Possible errors:
 --
 -- * `"parse error"` - if the URI can not be parsed
--- * `"ping was not sent"` - if hostname could not be reloved
--- * `"no reponce"` - if member does not responf within 0.2 seconds
+-- * `"ping was not sent"` - if hostname could not be resloved
+-- * `"no responce"` - if member does not respond within 0.2 seconds
 local function probe_uri(uri)
     checks('string')
     local parts = uri_tools.parse(uri)

membership/events.lua

@@ -23,6 +23,8 @@ local _expired = table.copy(stash.get('events._expired')) or {
 local _subscribers = table.copy(stash.get('events._subscribers')) or {
     -- [fiber.cond] = true
 }
+local _global_params = stash.get('global_params')
+
 setmetatable(_subscribers, {__mode = 'k'})
 
 function events.after_reload()
@@ -148,7 +150,8 @@ function events.handle(event)
             opts.STATUS_NAMES[event.status]
         )
     end
-    members.set(event.uri, event.status, event.incarnation, { payload = event.payload })
+    members.set(event.uri, event.status, event.incarnation, { payload = event.payload },
+        { forbid_new = _global_params.forbid_new_members })
 
     for cond, _ in pairs(_subscribers) do
         cond:broadcast()

membership/members.lua

@@ -84,10 +84,17 @@ function members.filter_excluding(state, uri1, uri2)
     return ret
 end
 
-function members.set(uri, status, incarnation, params)
-    checks('string', 'number', 'number', { payload = '?table', clock_delta = '?number' })
+function members.set(uri, status, incarnation, params, set_opts)
+    checks('string', 'number', 'number',
+        { payload = '?table', clock_delta = '?number', },
+        { forbid_new = '?boolean', }
+    )
 
     local member = _all_members[uri]
+    if member == nil and set_opts and set_opts.forbid_new then
+        opts.log_debug("New member %s was skipped", uri)
+        return
+    end
     if member and incarnation < member.incarnation then
         error('Can not downgrade incarnation')
     end

membership/stash.lua

@@ -1,4 +1,7 @@
 local S = rawget(_G, '__membership_stash') or {}
+S.global_params = S.global_params or {
+    forbid_new_members = false,
+}
 
 local log = require('log')