moonlibs / config

69%

master: 68%

Build Type

push

github

Committed by Vladislav Grubov

Commit Message

feat: support config.enforce_ro()

  * This method is needed for autofailover mechanisms mainly to enforce
    read_only=true during loading phase of tarantool.

  Before this patch race condition existed between autofailover and
  moonlibs/config recovering behaviour.

  If master crashes but fastly restarts then it initiates long running
  loading phase. Master recovers as read_only=true but after returning
  from box.cfg moonlibs/config retrieves config from ETCD and rechecks
  read_only option.

  The race happens when autofailover changes configuration in ETCD, but
  master just in time returns from loading phase and applies oldest
  configuration. This leads cluster to split-brain.

  With method config.enforce_ro it is possible for external coordinator
  firstly enforce_ro on loading leader and receive approval that leader
  will not be promoted to rw until next reload configuration.

  tarantool is enforcable to be ro only when all of the following conditions
  are met:
	1) Tarantool is recovering from snapshot (it was already
	   bootstrapped)
	2) Client's code do not override box.cfg with passing args.boxcfg
	3) args.tidy_load is enabled (default, but can be overriden by
	   client)
	4) config uses ETCD to retreive topology.

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