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:
*`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`. 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.
*`ping_timeout`: How long to wait for existing EC2 nodes to reply during discovery. Defaults to `3s`. If no unit like `ms`, `s` or `m` is specified, milliseconds are used.
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.
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.
### 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.
*`chunk_size`: Big files can be broken down into chunks during snapshotting if needed. The chunk size can be specified in bytes or by using size value notation, i.e. `1g`, `10m`, `5k`. Defaults to `100m`.
*`compress`: When set to `true` metadata files are stored in compressed format. This setting doesn't affect index files that are already compressed by default. Defaults to `false`.
In order to restrict the Elasticsearch snapshot process to the minimum required resources, we recommend using Amazon IAM in conjunction with pre-existing S3 buckets. Here is an example policy which will allow the snapshot access to an S3 bucket named "snaps.example.com". This may be configured through the AWS IAM console, by creating a Custom Policy, and using a Policy Document similar to this (changing snaps.example.com to your bucket name).
```js
{
"Statement": [
{
"Action": [
"s3:ListBucket"
],
"Effect": "Allow",
"Resource": [
"arn:aws:s3:::snaps.example.com"
]
},
{
"Action": [
"s3:GetObject",
"s3:PutObject",
"s3:DeleteObject"
],
"Effect": "Allow",
"Resource": [
"arn:aws:s3:::snaps.example.com/*"
]
}
],
"Version": "2012-10-17"
}
```
You may further restrict the permissions by specifying a prefix within the bucket, in this example, named "foo".
The bucket needs to exist to register a repository for snapshots. If you did not create the bucket then the repository registration will fail. If you want elasticsearch to create the bucket instead, you can add the permission to create a specific bucket like this:
Integrations tests in this plugin require working AWS configuration and therefore disabled by default. Three buckets and two iam users have to be created. The first iam user needs access to two buckets in different regions and the final bucket is exclusive for the other iam user. To enable tests prepare a config file elasticsearch.yml with the following content:
Replace all occurrences of `access_key`, `secret_key`, `bucket` and `region` with your settings. Please, note that the test will delete all snapshot/restore related files in the specified buckets.
