Configure the instance metadata options - Amazon Elastic Compute Cloud
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Configure the instance metadata options

The instance metadata service (IMDS) runs locally on every EC2 instance. The instance metadata options refer to a set of configurations that control the accessibility and behavior of the IMDS on an EC2 instance.

You can configure the following instance metadata options on each instance:

Instance metadata service (IMDS): enabled | disabled

You can enable or disable the IMDS on an instance. When disabled, you or any code won't be able to access the instance metadata on the instance.

The IMDS has two endpoints on an instance: IPv4 (169.254.169.254) and IPv6 ([fd00:ec2::254]). When you enable the IMDS, the IPv4 endpoint is automatically enabled. If you want to enable the IPv6 endpoint, you need to do so explicitly.

IMDS IPv6 endpoint: enabled | disabled

You can explicitly enable the IPv6 IMDS endpoint on an instance. When the IPv6 endpoint is enabled, the IPv4 endpoint remains enabled. The IPv6 endpoint is only supported on instances built on the Amazon Nitro System.

Metadata version: IMDSv1 or IMDSv2 (token optional) | IMDSv2 only (token required)

When requesting instance metadata, IMDSv2 calls require a token. IMDSv1 calls do not require a token. You can configure an instance to allow either IMDSv1 or IMDSv2 calls (where a token is optional), or to only allow IMDSv2 calls (where a token is required).

Metadata response hop limit: 164

The hop limit is the number of network hops that the PUT response is allowed to make. You can set the hop limit to a minimum of 1 and a maximum of 64. In a container environment, we recommend setting the hop limit to 2. For more information, see Considerations.

Access to tags in instance metadata: enabled | disabled

You can enable or disable access to the instance's tags from an instance's metadata. For more information, see Work with instance tags in instance metadata.

Where to configure instance metadata options

Instance metadata options can be configured at different levels, as follows:

  • Account – You can set default values for the instance metadata options at the account level for each Amazon Web Services Region. When an instance is launched, the instance metadata options are automatically set to the account-level values. You can change these values at launch. Account-level default values do not affect existing instances.

  • AMI – You can set the imds-support parameter to v2.0 when you register or modify an AMI. When an instance is launched with this AMI, the instance metadata version is automatically set to IMDSv2 and the hop limit is set to 2.

  • Instance – You can change all the instance metadata options on an instance at launch, overriding the default settings. You can also change the instance metadata options after launch on a running or stopped instance. Note that changes may be restricted by an IAM or SCP policy.

For more information, see Configure instance metadata options for new instances and Modify instance metadata options for existing instances.

Order of precedence for instance metadata options

The value for each instance metadata option is determined at instance launch, following a hierarchical order of precedence. The hierarchy, with the highest precedence at the top, is as follows:

  • Precedence 1: Instance configuration at launch – Values can be specified either in the launch template or in the instance configuration. Any values specified here override values specified at the account level or in the AMI.

  • Precedence 2: Account settings – If a value is not specified at instance launch, then it is determined by the account-level settings (which are set for each Amazon Web Services Region). Account-level settings either include a value for each metadata option, or indicate no preference at all.

  • Precedence 3: AMI configuration – If a value is not specified at instance launch or at the account level, then it is determined by the AMI configuration. This applies only to HttpTokens and HttpPutResponseHopLimit.

Each metadata option is evaluated separately. The instance can be configured with a mix of direct instance configuration, account-level defaults, and the configuration from the AMI.

You can change the value of any metadata option after launch on a running or stopped instance, unless changes are restricted by an IAM or SCP policy.

Determine values for metadata options – Example 1

In this example, an EC2 instance is launched into a Region where the HttpPutResponseHopLimit is set to 1 at the account level. The specified AMI has ImdsSupport set to v2.0. No metadata options are specified directly on the instance at launch. The instance is launched with the following metadata options:

"MetadataOptions": { ... "HttpTokens": "required", "HttpPutResponseHopLimit": 1, ...

These values were determined as follows:

  • No metadata options specified at launch: During the launch of the instance, specific values for the metadata options were not provided either in the instance launch parameters or in the launch template.

  • Account settings take next precedence: In the absence of specific values specified at launch, the settings at the account level within the Region take precedence. This means that the default values configured at the account level are applied. In this case, the HttpPutResponseHopLimit was set to 1.

  • AMI settings take last precedence: In the absence of a specific value specified at launch or at the account level for HttpTokens (the instance metadata version), the AMI setting is applied. In this case, the AMI setting ImdsSupport: v2.0 determined that HttpTokens was set to required. Note that while the AMI setting ImdsSupport: v2.0 is designed to set HttpPutResponseHopLimit: 2, it was overridden by the account-level setting HttpPutResponseHopLimit: 1, which has higher precedence.

Determine values for metadata options – Example 2

In this example, the EC2 instance is launched with the same settings as in the previous Example 1, but with HttpTokens set to optional directly on the instance at launch. The instance is launched with the following metadata options:

"MetadataOptions": { ... "HttpTokens": "optional", "HttpPutResponseHopLimit": 1, ...

The value for HttpPutResponseHopLimit is determined in the same way as in Example 1. However, the value for HttpTokens is determined as follows: Metadata options configured on the instance at launch take first precedence. Even though the AMI was configured with ImdsSupport: v2.0 (in other words, HttpTokens is set to required), the value specified on the instance at launch (HttpTokens set to optional) took precedence.

Set the instance metadata version

When an instance is launched, the value for the instance metadata version is either IMDSv1 or IMDSv2 (token optional) or IMDSv2 only (token required).

At instance launch, you can either manually specify the value for the metadata version, or use the default value. If you manually specify the value, it overrides any defaults. If you opt not to manually specify the value, it will be determined by a combination of default settings, as outlined in the following table.

The table shows how the metadata version for an instance at launch (indicated by Resulting instance configuration in column 4) is determined by the settings at the different levels of configuration. The order of precedence is from left to right, where the first column takes the highest precedence, as follows:

  • Column 1: Launch parameter – Represents the setting on the instance that you manually specify at launch.

  • Column 2: Account level default – Represents the setting for the account.

  • Column 3: AMI default – Represents the setting on the AMI.

Launch parameter Account level default AMI default Resulting instance configuration
V2 only (token required) No preference V2 only V2 only
V2 only (token required) V2 only V2 only V2 only
V2 only (token required) V1 or V2 V2 only V2 only
V1 or V2 (token optional) No preference V2 only V1 or V2
V1 or V2 (token optional) V2 only V2 only V1 or V2
V1 or V2 (token optional) V1 or V2 V2 only V1 or V2
Not set No preference V2 only V2 only
Not set V2 only V2 only V2 only
Not set V1 or V2 V2 only V1 or V2
V2 only (token required) No preference null V2 only
V2 only (token required) V2 only null V2 only
V2 only (token required) V1 or V2 null V2 only
V1 or V2 (token optional) No preference null V1 or V2
V1 or V2 (token optional) V2 only null V1 or V2
V1 or V2 (token optional) V1 or V2 null V1 or V2
Not set No preference null V1 or V2
Not set V2 only null V2 only
Not set V1 or V2 null V1 or V2

Use IAM condition keys to restrict instance metadata options

You can use IAM condition keys in an IAM policy or SCP as follows:

  • Allow an instance to launch only if it's configured to require the use of IMDSv2

  • Restrict the number of allowed hops

  • Turn off access to instance metadata

Note

You should proceed cautiously and conduct careful testing before making any changes. Take note of the following:

  • If you enforce the use of IMDSv2, applications or agents that use IMDSv1 for instance metadata access will break.

  • If you turn off all access to instance metadata, applications or agents that rely on instance metadata access to function will break.

  • For IMDSv2, you must use /latest/api/token when retrieving the token.