IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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EC2 Discovery

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EC2 Discovery

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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:

discovery:
    zen.hosts_provider: ec2

You must also set cloud.aws.region if you are not using default AWS region. See Region for details.

The ec2 discovery is using the same credentials as the rest of the AWS services provided by this plugin (repositories). See Getting started with AWS for details.

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

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. (NOTE: You could provide either group NAME or group ID.)

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 or tag:TAGNAME where TAGNAME refers to a name of a tag configured for all EC2 instances. Instances which don’t have this tag set will be ignored by the discovery process.

For example if you defined a tag my-elasticsearch-host in ec2 and set it to myhostname1.mydomain.com, then setting host_type: tag:my-elasticsearch-host will tell Discovery Ec2 plugin to read the host name from the my-elasticsearch-host tag. In this case, it will be resolved to myhostname1.mydomain.com. Read more about EC2 Tags.

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.

node_cache_time

How long the list of hosts is cached to prevent further requests to the AWS API. Defaults to 10s.

Binding the network host

It’s important to define network.host as by default it’s bound to localhost.

You can use core network host settings or ec2 specific host settings:

EC2 Network Host

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When the discovery-ec2 plugin is installed, the following are also allowed as valid network host settings:

EC2 Host Value	Description
`_ec2:privateIpv4_`	The private IP address (ipv4) of the machine.
`_ec2:privateDns_`	The private host of the machine.
`_ec2:publicIpv4_`	The public IP address (ipv4) of the machine.
`_ec2:publicDns_`	The public host of the machine.
`_ec2:privateIp_`	equivalent to `_ec2:privateIpv4_`.
`_ec2:publicIp_`	equivalent to `_ec2:publicIpv4_`.
`_ec2_`	equivalent to `_ec2:privateIpv4_`.

Recommended EC2 Permissions

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EC2 discovery requires making a call to the EC2 service. You’ll want to setup an IAM policy to allow this. You can create a custom policy via the IAM Management Console. It should look similar to this.

{
  "Statement": [
    {
      "Action": [
        "ec2:DescribeInstances"
      ],
      "Effect": "Allow",
      "Resource": [
        "*"
      ]
    }
  ],
  "Version": "2012-10-17"
}

Filtering by Tags

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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 discovery.zen.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.

Automatic Node Attributes

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Though not dependent on actually using ec2 as discovery (but still requires the discovery-ec2 plugin installed), the plugin can automatically add node attributes relating to ec2. In the future this may support other attributes, but this will currently only add an aws_availability_zone node attribute, which is the availability zone of the current node. Attributes can be used to isolate primary and replica shards across availability zones by using the Allocation Awareness feature.

In order to enable it, set cloud.node.auto_attributes to true in the settings. For example:

cloud.node.auto_attributes: true

cluster.routing.allocation.awareness.attributes: aws_availability_zone

Using other EC2 endpoint

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If you are using any EC2 api compatible service, you can set the endpoint you want to use by setting cloud.aws.ec2.endpoint to your URL provider.

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