Why is my new AWS elasticsearch always Yellow?

Question

• I've just made a new AWS ES domain
• it's a single node
• nothing is in it yet

Q: the cluster never turns green! Why?

Here's the characteristics of the cluster:

Instance type       t2.small.elasticsearch
Instance count       1
Dedicated master       Disabled
Zone awareness       Disabled
Storage type       EBS
EBS volume type       General Purpose (SSD)
EBS volume size       10 GB
Encryption at rest       Disabled
Start hour for the daily automated snapshot       09:00 UTC

Advanced options
Elasticsearch parameters:
rest.action.multi.allow_explicit_index: true
indices.fielddata.cache.size: unbounded (default)
indices.query.bool.max_clause_count: 1024 (default)

Answer 1

CAUSE #1: From Handling AWS Service Errors:

A yellow cluster status means that the primary shards for all indices are allocated to nodes in a cluster, but the replica shards for at least one index are not. Single-node clusters always initialize with a yellow cluster status because there is no other node that Amazon ES can assign a replica to. To achieve green cluster status, increase your node count. For more information, see Configuring Amazon ES Domains in this guide and Update Indices Settings in the Elasticsearch documentation.

CAUSE #2:

If you have Kibana installed, it is probably because there is a replica shard for the .kibana index. If you remove that replica shard, your cluster will turn green.