# Metadata service

Note

This section provides deployment information about the metadata service. For end-user information about the metadata service and instance metadata in general, refer to the user guide.

The metadata service provides a way for instances to retrieve instance-specific data. Instances access the metadata service at `http://169.254.169.254`. The metadata service supports two sets of APIs - an OpenStack metadata API and an EC2-compatible API - and also exposes vendordata and user data. Both the OpenStack metadata and EC2-compatible APIs are versioned by date.

The metadata service can be run globally, as part of the nova-api application, or on a per-cell basis, as part of the standalone nova-api-metadata application. A detailed comparison is provided in the cells V2 guide.

Changed in version 19.0.0: The ability to run the nova metadata API service on a per-cell basis was added in Stein. For versions prior to this release, you should not use the standalone nova-api-metadata application for multiple cells.

Guests access the service at `169.254.169.254` or at `fe80::a9fe:a9fe`.

Changed in version 22.0.0: Starting with the Victoria release the metadata service is accessible over IPv6 at the link-local address `fe80::a9fe:a9fe`.

The networking service, neutron, is responsible for intercepting these requests and adding HTTP headers which uniquely identify the source of the request before forwarding it to the metadata API server. For the Open vSwitch and Linux Bridge backends provided with neutron, the flow looks something like so:

1. Instance sends a HTTP request for metadata to `169.254.169.254`.

2. This request either hits the router or DHCP namespace depending on the route in the instance

3. The metadata proxy service in the namespace adds the following info to the request:

   - Instance IP (`X-Forwarded-For` header)

   - Router or Network-ID (`X-Neutron-Network-Id` or `X-Neutron-Router-Id` header)

4. The metadata proxy service sends this request to the metadata agent (outside the namespace) via a UNIX domain socket.

5. The neutron-metadata-agent application forwards the request to the nova metadata API service by adding some new headers (instance ID and Tenant ID) to the request.

This flow may vary if a different networking backend is used.

Neutron and nova must be configured to communicate together with a shared secret. Neutron uses this secret to sign the Instance-ID header of the metadata request to prevent spoofing. This secret is configured through the `neutron.metadata_proxy_shared_secret` config option in nova and the equivalent `metadata_proxy_shared_secret` config option in neutron.

## Configuration

The nova-api application accepts the following metadata service-related options:

- `enabled_apis`

- `enabled_ssl_apis`

- `neutron.service_metadata_proxy`

- `neutron.metadata_proxy_shared_secret`

- `api.metadata_cache_expiration`

- `api.local_metadata_per_cell`

- `api.dhcp_domain`

Note

This list excludes configuration options related to the vendordata feature. Refer to vendordata feature documentation for information on configuring this.

For example, to configure the nova-api application to serve the metadata API, without SSL, using the `StaticJSON` vendordata provider, add the following to a `nova-api.conf` file:

    [DEFAULT]
    enabled_apis = osapi_compute,metadata
    enabled_ssl_apis =
    metadata_listen = 0.0.0.0
    metadata_listen_port = 0
    metadata_workers = 4

    [neutron]
    service_metadata_proxy = True

    [api]
    dhcp_domain =
    metadata_cache_expiration = 15
    local_metadata_per_cell = False
    vendordata_providers = StaticJSON
    vendordata_jsonfile_path = /etc/nova/vendor_data.json

Note

This does not include configuration options that are not metadata-specific but are nonetheless required, such as `api.auth_strategy`.

Configuring the application to use the `DynamicJSON` vendordata provider is more involved and is not covered here.

The nova-api-metadata application accepts almost the same options:

- `neutron.service_metadata_proxy`

- `neutron.metadata_proxy_shared_secret`

- `api.metadata_cache_expiration`

- `api.local_metadata_per_cell`

- `api.dhcp_domain`

Note

This list excludes configuration options related to the vendordata feature. Refer to vendordata feature documentation for information on configuring this.

For example, to configure the nova-api-metadata application to serve the metadata API, without SSL, add the following to a `nova-api.conf` file:

    [DEFAULT]
    metadata_listen = 0.0.0.0
    metadata_listen_port = 0
    metadata_workers = 4

    [neutron]
    service_metadata_proxy = True

    [api]
    dhcp_domain =
    metadata_cache_expiration = 15
    local_metadata_per_cell = False

Note

This does not include configuration options that are not metadata-specific but are nonetheless required, such as `api.auth_strategy`.

For information about configuring the neutron side of the metadata service, refer to the neutron configuration guide

## Config drives

Config drives are special drives that are attached to an instance when it boots. The instance can mount this drive and read files from it to get information that is normally available through the metadata service. For more information, refer to Config drives and the user guide.

## Vendordata

Vendordata provides a way to pass vendor or deployment-specific information to instances. For more information, refer to Vendordata and the user guide.

## User data

User data is a blob of data that the user can specify when they launch an instance. For more information, refer to the user guide.

this page last updated: 2026-04-14 07:16:25

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