# How to add more masters to a cluster of one master whilst avoiding split-brain and downtime? **URL:** \ **Category:** Elasticsearch\ **Created:** [September 21, 2018, 12:57pm UTC](https://discuss.elastic.co/t/how-to-add-more-masters-to-a-cluster-of-one-master-whilst-avoiding-split-brain-and-downtime/149458 "2018-09-21T12:57:46Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![elastico](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/elastico/32/35758_2.png) [@elastico](https://discuss.elastic.co/u/elastico)\ **Post date:** [September 21, 2018, 12:57pm UTC](https://discuss.elastic.co/t/how-to-add-more-masters-to-a-cluster-of-one-master-whilst-avoiding-split-brain-and-downtime/149458/1 "2018-09-21T12:57:47Z")
I have a three node cluster with 1 master-data node and 2 data-only nodes. I want to make this into a 3 master-data node cluster without any downtime. To this effect, I planned to do the following: 1. First, set `discovery.zen.minimum_master: 2` setting dynamically via the REST API. 2. Second, set `node.master` and `node.data` to `true` in the config file of each data node and restart - one at a time. However, this may lead to split-brain since the current `discovery.zen.minimum_master` setting default to 1, and I have been suggested to do a full cluster restart to avoid this. But since that will cause downtime, is there a way around this? ---
**Author:** ![elastico](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/elastico/32/35758_2.png) [@elastico](https://discuss.elastic.co/u/elastico)\ **Post date:** [September 23, 2018, 9:14am UTC](https://discuss.elastic.co/t/how-to-add-more-masters-to-a-cluster-of-one-master-whilst-avoiding-split-brain-and-downtime/149458/2 "2018-09-23T09:14:13Z")
But if I do a rolling restart (after changing cluster quorum to 2 dynamically) whereby I change config on one data node (to make it master-data node) and restart, there could still be a split-brain since current master will self-elect while new master-eligible nodes would elect master too as they need 2 nodes to elect master. Hence, I have been suggested to do a full cluster restart to avoid this. But since cluster restart will cause downtime, is there a way around this? Elasticsearch version is 1.5 ---
**Author:** ![DavidTurner](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/davidturner/32/22453_2.png) [@DavidTurner](https://discuss.elastic.co/u/DavidTurner)\ **Post date:** [September 25, 2018, 12:57pm UTC](https://discuss.elastic.co/t/how-to-add-more-masters-to-a-cluster-of-one-master-whilst-avoiding-split-brain-and-downtime/149458/3 "2018-09-25T12:57:36Z")
No, there is at present no fully reliable way to change a cluster from having a single master node to having two master nodes for exactly the reasons you describe (although 2 to 3 works fine since no change to `minimum_master_nodes` is required). The only truly safe way to do this is with a full cluster restart. 1.5 hit end-of-life over two years ago, and has known resilience bugs. You should upgrade. Perhaps you could stand up a newer cluster alongside this one, use [reindex-from-remote](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-reindex.html#reindex-from-remote) to copy the data across, and then cut across to your new cluster without downtime. ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [October 23, 2018, 12:57pm UTC](https://discuss.elastic.co/t/how-to-add-more-masters-to-a-cluster-of-one-master-whilst-avoiding-split-brain-and-downtime/149458/4 "2018-10-23T12:57:39Z")
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