A voting-only master-eligible node is a node that can participate in master elections but will not act
as a master in the cluster. In particular, a voting-only node can help elect another master-eligible
node as master, and can serve as a tiebreaker in elections. High availability (HA) clusters require at
least three master-eligible nodes, so that if one of the three nodes is down, then the remaining two
can still elect a master amongst them-selves. This only requires one of the two remaining nodes to
have the capability to act as master, but both need to have voting powers. This means that one of
the three master-eligible nodes can be made as voting-only. If this voting-only node is a dedicated
master, a less powerful machine or a smaller heap-size can be chosen for this node. Alternatively, a
voting-only non-dedicated master node can play the role of the third master-eligible node, which
allows running an HA cluster with only two dedicated master nodes.
Closes#14340
Co-authored-by: David Turner <david.turner@elastic.co>
Expands and clarifies exactly what is and isn't allowed when specifying a
subset of the nodes as targets of a cluster API, and adds missing links to this
from the hot threads and cluster stats API docs.
Co-authored-by: David Turner <david.turner@elastic.co>
Co-authored-by: Yu <yu.liu003@gmail.com>
* plugins/discovery-azure-class.asciidoc
* reference/cluster.asciidoc
* reference/modules/cluster/misc.asciidoc
* reference/modules/indices/request_cache.asciidoc
After this is merged there will be no unconvereted snippets outside
of `reference`.
Related to #18160
This adds a new `/_cluster/allocation/explain` API that explains why a
shard can or cannot be allocated to nodes in the cluster. Additionally,
it will show where the master *desires* to put the shard, according to
the `ShardsAllocator`.
It looks like this:
```
GET /_cluster/allocation/explain?pretty
{
"index": "only-foo",
"shard": 0,
"primary": false
}
```
Though, you can optionally send an empty body, which means "explain the
allocation for the first unassigned shard you find".
The output when a shard is unassigned looks like this:
```
{
"shard" : {
"index" : "only-foo",
"index_uuid" : "KnW0-zELRs6PK84l0r38ZA",
"id" : 0,
"primary" : false
},
"assigned" : false,
"unassigned_info" : {
"reason" : "INDEX_CREATED",
"at" : "2016-03-22T20:04:23.620Z"
},
"nodes" : {
"V-Spi0AyRZ6ZvKbaI3691w" : {
"node_name" : "Susan Storm",
"node_attributes" : {
"bar" : "baz"
},
"final_decision" : "NO",
"weight" : 0.06666675,
"decisions" : [ {
"decider" : "filter",
"decision" : "NO",
"explanation" : "node does not match index include filters [foo:\"bar\"]"
} ]
},
"Qc6VL8c5RWaw1qXZ0Rg57g" : {
"node_name" : "Slipstream",
"node_attributes" : {
"bar" : "baz",
"foo" : "bar"
},
"final_decision" : "NO",
"weight" : -1.3833332,
"decisions" : [ {
"decider" : "same_shard",
"decision" : "NO",
"explanation" : "the shard cannot be allocated on the same node id [Qc6VL8c5RWaw1qXZ0Rg57g] on which it already exists"
} ]
},
"PzdyMZGXQdGhqTJHF_hGgA" : {
"node_name" : "The Symbiote",
"node_attributes" : { },
"final_decision" : "NO",
"weight" : 2.3166666,
"decisions" : [ {
"decider" : "filter",
"decision" : "NO",
"explanation" : "node does not match index include filters [foo:\"bar\"]"
} ]
}
}
}
```
And when the shard *is* assigned, the output looks like:
```
{
"shard" : {
"index" : "only-foo",
"index_uuid" : "KnW0-zELRs6PK84l0r38ZA",
"id" : 0,
"primary" : true
},
"assigned" : true,
"assigned_node_id" : "Qc6VL8c5RWaw1qXZ0Rg57g",
"nodes" : {
"V-Spi0AyRZ6ZvKbaI3691w" : {
"node_name" : "Susan Storm",
"node_attributes" : {
"bar" : "baz"
},
"final_decision" : "NO",
"weight" : 1.4499999,
"decisions" : [ {
"decider" : "filter",
"decision" : "NO",
"explanation" : "node does not match index include filters [foo:\"bar\"]"
} ]
},
"Qc6VL8c5RWaw1qXZ0Rg57g" : {
"node_name" : "Slipstream",
"node_attributes" : {
"bar" : "baz",
"foo" : "bar"
},
"final_decision" : "CURRENTLY_ASSIGNED",
"weight" : 0.0,
"decisions" : [ {
"decider" : "same_shard",
"decision" : "NO",
"explanation" : "the shard cannot be allocated on the same node id [Qc6VL8c5RWaw1qXZ0Rg57g] on which it already exists"
} ]
},
"PzdyMZGXQdGhqTJHF_hGgA" : {
"node_name" : "The Symbiote",
"node_attributes" : { },
"final_decision" : "NO",
"weight" : 3.6999998,
"decisions" : [ {
"decider" : "filter",
"decision" : "NO",
"explanation" : "node does not match index include filters [foo:\"bar\"]"
} ]
}
}
}
```
Only "NO" decisions are returned by default, but all decisions can be
shown by specifying the `?include_yes_decisions=true` parameter in the
request.
Resolves#14593
Yannick Welsch
Lisa Cawley
Yu
Sohaib Iftikhar
Spencer
Nik Everett
Jason Tedor
Igor Motov
Clinton Gormley
Lee Hinman
Simon Willnauer
Alexander Reelsen
Boaz Leskes