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EC2 Discovery Plugin

The EC2 discovery plugin uses the AWS API for unicast discovery.

If you are looking for a hosted solution of Elasticsearch on AWS, please visit http://www.elastic.co/cloud.

Installation

This plugin can be installed using the plugin manager:

sudo bin/elasticsearch-plugin install discovery-ec2

The plugin must be installed on every node in the cluster, and each node must be restarted after installation.

This plugin can be downloaded for offline install from {plugin_url}/discovery-ec2/discovery-ec2-{version}.zip.

Removal

The plugin can be removed with the following command:

sudo bin/elasticsearch-plugin remove discovery-ec2

The node must be stopped before removing the plugin.

Getting started with AWS

The plugin provides a hosts provider for zen discovery named ec2. This hosts provider finds other Elasticsearch instances in EC2 through AWS metadata. Authentication is done using IAM Role credentials by default. To enable the plugin, set the unicast host provider for Zen discovery to ec2:

discovery.zen.hosts_provider: ec2

Settings

EC2 host discovery supports a number of settings. Some settings are sensitive and must be stored in the {ref}/secure-settings.html[elasticsearch keystore]. For example, to use explicit AWS access keys:

bin/elasticsearch-keystore add discovery.ec2.access_key
bin/elasticsearch-keystore add discovery.ec2.secret_key

The following are the available discovery settings. All should be prefixed with discovery.ec2.. Those that must be stored in the keystore are marked as Secure.

access_key

An ec2 access key. The secret_key setting must also be specified. (Secure)

secret_key

An ec2 secret key. The access_key setting must also be specified. (Secure)

session_token

An ec2 session token. The access_key and secret_key settings must also be specified. (Secure)

endpoint

The ec2 service endpoint to connect to. See http://docs.aws.amazon.com/general/latest/gr/rande.html#ec2_region. This defaults to ec2.us-east-1.amazonaws.com.

protocol

The protocol to use to connect to ec2. Valid values are either http or https. Defaults to https.

proxy.host

The host name of a proxy to connect to ec2 through.

proxy.port

The port of a proxy to connect to ec2 through.

proxy.username

The username to connect to the proxy.host with. (Secure)

proxy.password

The password to connect to the proxy.host with. (Secure)

read_timeout

The socket timeout for connecting to ec2. The value should specify the unit. For example, a value of 5s specifies a 5 second timeout. The default value is 50 seconds.

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.

All secure settings of this plugin are {ref}/secure-settings.html#reloadable-secure-settings[reloadable]. After you reload the settings, an aws sdk client with the latest settings from the keystore will be used.

Important
Binding the network host

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

You can use {ref}/modules-network.html[core network host settings] or ec2 specific host settings:

EC2 Network Host

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

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

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, if you defined a tag stage in EC2 and set it to dev, setting discovery.ec2.tag.stage to dev will only filter instances with a tag key set to stage, and a value of dev. Adding multiple discovery.ec2.tag settings 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

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 {ref}/allocation-awareness.html[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

Best Practices in AWS

Collection of best practices and other information around running Elasticsearch on AWS.

Instance/Disk

When selecting disk please be aware of the following order of preference:

  • EFS - Avoid as the sacrifices made to offer durability, shared storage, and grow/shrink come at performance cost, such file systems have been known to cause corruption of indices, and due to Elasticsearch being distributed and having built-in replication, the benefits that EFS offers are not needed.

  • EBS - Works well if running a small cluster (1-2 nodes) and cannot tolerate the loss all storage backing a node easily or if running indices with no replicas. If EBS is used, then leverage provisioned IOPS to ensure performance.

  • Instance Store - When running clusters of larger size and with replicas the ephemeral nature of Instance Store is ideal since Elasticsearch can tolerate the loss of shards. With Instance Store one gets the performance benefit of having disk physically attached to the host running the instance and also the cost benefit of avoiding paying extra for EBS.

Prefer Amazon Linux AMIs as since Elasticsearch runs on the JVM, OS dependencies are very minimal and one can benefit from the lightweight nature, support, and performance tweaks specific to EC2 that the Amazon Linux AMIs offer.

Networking
  • Networking throttling takes place on smaller instance types in both the form of bandwidth and number of connections. Therefore if large number of connections are needed and networking is becoming a bottleneck, avoid instance types with networking labeled as Moderate or Low.

  • Multicast is not supported, even when in an VPC; the aws cloud plugin which joins by performing a security group lookup.

  • When running in multiple availability zones be sure to leverage {ref}/allocation-awareness.html[shard allocation awareness] so that not all copies of shard data reside in the same availability zone.

  • Do not span a cluster across regions. If necessary, use cross cluster search.

Misc
  • If you have split your nodes into roles, consider tagging the EC2 instances by role to make it easier to filter and view your EC2 instances in the AWS console.

  • Consider enabling termination protection for all of your instances to avoid accidentally terminating a node in the cluster and causing a potentially disruptive reallocation.