Ec2

ec2 discovery allows to use the ec2 APIs to perform automatic discovery (similar to multicast in non hostile multicast environments). Here is a simple sample configuration:

cloud:
    aws:
        access_key: AKVAIQBF2RECL7FJWGJQ
        secret_key: vExyMThREXeRMm/b/LRzEB8jWwvzQeXgjqMX+6br

discovery:
    type: ec2

You’ll need to install the cloud-aws plugin, by running bin/plugin install cloud-aws before (re)starting elasticsearch.

The following are a list of settings (prefixed with discovery.ec2) that can further control the discovery:

Setting	Description
groups	Either a comma separated list or array based list of (security) groups. Only instances with the provided security groups will be used in the cluster discovery.
host_type	The type of host type to use to communicate with other instances. Can be one of private_ip, public_ip, private_dns, public_dns. Defaults to private_ip.
availability_zones	Either a comma separated list or array based list of availability zones. Only instances within the provided availability zones will be used in the cluster discovery.
any_group	If set to false, will require all security groups to be present for the instance to be used for the discovery. Defaults to true.
ping_timeout	How long to wait for existing EC2 nodes to reply during discovery. Defaults to 3s.

Filtering by Tags

The ec2 discovery can also filter machines to include in the cluster based on tags (and not just groups). The settings to use include the discovery.ec2.tag. prefix. For example, setting discovery.ec2.tag.stage to dev will only filter instances with a tag key set to stage, and a value of dev. Several tags set will require all of those tags to be set for the instance to be included.

One practical use for tag filtering is when an ec2 cluster contains many nodes that are not running elasticsearch. In this case (particularly with high ping_timeout values) there is a risk that a new node’s discovery phase will end before it has found the cluster (which will result in it declaring itself master of a new cluster with the same name - highly undesirable). Tagging elasticsearch ec2 nodes and then filtering by that tag will resolve this issue.

Region

The cloud.aws.region can be set to a region and will automatically use the relevant settings for both ec2 and s3. The available values are: us-east-1, us-west-1, ap-southeast-1, eu-west-1.

Automatic Node Attributes

Though not dependent on actually using ec2 as discovery (but still requires the cloud aws plugin installed), the plugin can automatically add node attributes relating to ec2 (for example, availability zone, that can be used with the awareness allocation feature). In order to enable it, set cloud.node.auto_attributes to true in the settings.