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API Special Interest Group/Current Design/Metadata

Analysis

When a service has a metadata resource it typically takes the form of

{
  "metadata": {
    "key1": "value1",
    "key2": "value2"
  }
}

There doesn't seem to be a strong consensus about how the metadata is CRUDed.

The outliers are Orchestration's Software Configuration metadata which seems to describe a concept different from the other services notion of metadata and Object Storage's metadata which does everything with headers.

The Glance API (both v1 and v2) supports a rich metadata API, but it doesn't call these things "metadata", because it's not metadata technically. It's just data. Metadata is data *about* data -- e.g. the length of a string is metadata. The string is data. The length is data about the data. The Glance API calls these things "properties".

Current Design

Server

http://developer.openstack.org/api-ref-compute-v2.html#compute_server_metadata

{
  "metadata": {
    "name": "test_server",
    "server_type": "test"
  }
}
Method Path Description
GET /v2/​{tenant_id}​/servers/​{server_id}​/metadata Show server metadata
PUT /v2/​{tenant_id}​/servers/​{server_id}​/metadata Create or replace server metadata items
POST /v2/​{tenant_id}​/servers/​{server_id}​/metadata Update server metadata items
GET /v2/​{tenant_id}​/servers/​{server_id}​/metadata/​{key} ​Show server metadata item details
PUT /v2/​{tenant_id}​/servers/​{server_id}​/metadata/​{key} ​Create or update server metadata item
DELETE /v2/​{tenant_id}​/servers/​{server_id}​/metadata/​{key}​ Delete server metadata item

Image Properties in Glance v1 API

HTTP/1.1 204 No Content
x-image-meta-name             Ubuntu 10.04 Plain 5GB
x-image-meta-disk-format      vhd
x-image-meta-container-format ovf
x-image-meta-size             5368709120
x-image-meta-checksum         c2e5db72bd7fd153f53ede5da5a06de3
x-image-meta-created_at       2010-02-03 09:34:01
x-image-meta-updated_at       2010-02-03 09:34:01
x-image-meta-deleted_at
x-image-meta-status           available
x-image-meta-is-public        true
x-image-meta-owner            null
x-image-meta-property-distro  Ubuntu 10.04 LTS

You will note that all information about a disk image or snapshot is returned as HTTP headers. All header start with *x-image-meta*, because the data in the case of Glance is the disk image bytes. The term "metadata" that is used in other OpenStack APIs to refer to free-form key/value data about, say, a server, is called "properties" in Glance, and any HTTP header that begins with *x-image-meta-property* indicates one of these properties for the image. Above, the free-form property *distro* has a value of *Ubunut 10.04 LTS*.

Method Path Description
HEAD /v1/images/​{image_id}​ Returns all image properties as HTTP headers
PUT /v1/images/​{image_id} Create or replace image properties as HTTP headers
POST /v1/images/​{image_id} Update image properties as HTTP headers

Image Tags in Glance v2 API

{
    "id": "da3b75d9-3f4a-40e7-8a2c-bfab23927dea",
    "name": "cirros-0.3.0-x86_64-uec-ramdisk",
    "status": "active",
    "visibility": "public",
    "size": 2254249,
    "checksum": "2cec138d7dae2aa59038ef8c9aec2390",
    "tags": ["ping", "pong"],
    "created_at": "2012-08-10T19:23:50Z",
    "updated_at": "2012-08-10T19:23:50Z",
    "self": "/v2/images/da3b75d9-3f4a-40e7-8a2c-bfab23927dea",
    "file": "/v2/images/da3b75d9-3f4a-40e7-8a2c-bfab23927dea/file",
    "schema": "/v2/schemas/image"
}

The Glance v2 API has the concept of simple string tags, instead of key/value properties on an image. The tags are returned as a list of strings in the "tags" attribute of the top-most JSON document for an image in a call to the GET /v2/images/{image_id} API call.

Method Path Description
GET /v2/images/​{image_id}​ Returns all image information and tags
PATCH /v2/images/​{image_id} Create or replace image tags
PUT /v2/images/{image_id}/tags/{tag} Add tag to an image
DELETE /v2/images/{image_id}/tags/{tag} Remove tag from an image

Snapshot

http://developer.openstack.org/api-ref-blockstorage-v2.html#snapshots-v2

{
  "metadata": {
    "key": "v2"
  }
}
Method Path Description
GET /v2/​{tenant_id}​/snapshots/​{snapshot_id}​/metadata Show snapshot metadata
PUT /v2/​{tenant_id}​/snapshots/​{snapshot_id}​/metadata Update snapshot metadata

One or more metadata key and value pairs to set or unset for the snapshot.
To unset a metadata key value, specify only the key name.
To set a metadata key value, specify the key and value pair.

Stack

http://developer.openstack.org/api-ref-orchestration-v1.html#stack-resources

{
  "metadata": {
    "some_key": "some_value",
    "some_other_key": "some_other_value"
  }
}
Method Path Description
GET /v1/​{tenant_id}​/stacks/​{stack_name}​/​{stack_id}​/resources/​{resource_name}​/metadata Show resource metadata

Software Configuration

http://developer.openstack.org/api-ref-orchestration-v1.html#software-config

{
  "metadata": [
    {
      "inputs": [
        {
          "default": null,
          "type": "String",
          "name": "foo",
          "value": "fooooo",
          "description": null
        },
        {
          "default": null,
          "type": "String",
          "name": "bar",
          "value": "baaaaa",
          "description": null
        },
        {
          "type": "String",
          "name": "deploy_server_id",
          "value": "ec14c864-096e-4e27-bb8a-2c2b4dc6f3f5",
          "description": "ID of the server being deployed to"
        },
        {
          "type": "String",
          "name": "deploy_action",
          "value": "CREATE",
          "description": "Name of the current action being deployed"
        },
        {
          "type": "String",
          "name": "deploy_stack_id",
          "value": "a/9bd57090-8954-48ab-bab9-adf9e1ac70fc",
          "description": "ID of the stack this deployment belongs to"
        },
        {
          "type": "String",
          "name": "deploy_resource_name",
          "value": "deployment",
          "description": "Name of this deployment resource in the stack"
        },
        {
          "type": "String",
          "name": "deploy_signal_id",
          "value": "http://192.168.20.103:8000/v1/signal/arn%3Aopenstack%3Aheat%3A%3Ae2a84fbdaeb047ae8da4b503f3b69f1f%3Astacks%2Fa%2F9bd57090-8954-48ab-bab9-adf9e1ac70fc%2Fresources%2Fdeployment?Timestamp=2014-03-19T20%3A30%3A59Z&SignatureMethod=HmacSHA256&AWSAccessKeyId=ca3571413e4a49998d580215517b3685&SignatureVersion=2&Signature=w6Iu%2BNbg86mqwSOUf1GLuKPO7KaD82PiGpL4ig9Q1l4%3D",
          "description": "ID of signal to use for signalling output values"
        }
      ],
      "group": "script",
      "name": "a-config-we5zpvyu7b5o",
      "outputs": [
        {
          "type": "String",
          "name": "result",
          "error_output": false,
          "description": null
        }
      ],
      "options": null,
      "config": "#!/bin/sh -x\necho \"Writing to /tmp/$bar\"\necho $foo > /tmp/$bar\necho -n \"The file /tmp/$bar contains `cat /tmp/$bar` for server $deploy_server_id during $deploy_action\" > $heat_outputs_path.result\necho \"Written to /tmp/$bar\"\necho \"Output to stderr\" 1>&2",
      "id": "3d5ec2a8-7004-43b6-a7f6-542bdbe9d434"
    },
    {
      "inputs": [
        {
          "default": null,
          "type": "String",
          "name": "foo",
          "value": "fu",
          "description": null
        },
        {
          "default": null,
          "type": "String",
          "name": "bar",
          "value": "barmy",
          "description": null
        },
        {
          "type": "String",
          "name": "deploy_server_id",
          "value": "ec14c864-096e-4e27-bb8a-2c2b4dc6f3f5",
          "description": "ID of the server being deployed to"
        },
        {
          "type": "String",
          "name": "deploy_action",
          "value": "CREATE",
          "description": "Name of the current action being deployed"
        },
        {
          "type": "String",
          "name": "deploy_stack_id",
          "value": "a/9bd57090-8954-48ab-bab9-adf9e1ac70fc",
          "description": "ID of the stack this deployment belongs to"
        },
        {
          "type": "String",
          "name": "deploy_resource_name",
          "value": "other_deployment",
          "description": "Name of this deployment resource in the stack"
        },
        {
          "type": "String",
          "name": "deploy_signal_id",
          "value": "http://192.168.20.103:8000/v1/signal/arn%3Aopenstack%3Aheat%3A%3Ae2a84fbdaeb047ae8da4b503f3b69f1f%3Astacks%2Fa%2F9bd57090-8954-48ab-bab9-adf9e1ac70fc%2Fresources%2Fother_deployment?Timestamp=2014-03-19T20%3A30%3A59Z&SignatureMethod=HmacSHA256&AWSAccessKeyId=7b761482f8254946bcd3d5ccb36fe939&SignatureVersion=2&Signature=giMfv%2BhrAw6y%2FCMKQIQz2IhO5PkAj5%2BfP5YsL6rul3o%3D",
          "description": "ID of signal to use for signalling output values"
        }
      ],
      "group": "script",
      "name": "a-config-we5zpvyu7b5o",
      "outputs": [
        {
          "type": "String",
          "name": "result",
          "error_output": false,
          "description": null
        }
      ],
      "options": null,
      "config": "#!/bin/sh -x\necho \"Writing to /tmp/$bar\"\necho $foo > /tmp/$bar\necho -n \"The file /tmp/$bar contains `cat /tmp/$bar` for server $deploy_server_id during $deploy_action\" > $heat_outputs_path.result\necho \"Written to /tmp/$bar\"\necho \"Output to stderr\" 1>&2",
      "id": "8da95794-2ad9-4979-8ae5-739ce314c5cd"
    }
  ]
}
Method Path Description
GET /v1/​{tenant_id}​/software_deployments/metadata/​{server_id}​ Show server configuration metadata


Container

http://developer.openstack.org/api-ref-objectstorage-v1.html#storage_container_services

HTTP/1.1 204 No Content
X-Container-Meta-Author: SamuelClemens
Method Path Description
POST /v1/​{account}​/​{container}​ Create, update, or delete container metadata
HEAD /v1/​{account}​/​{container}​ Show container metadata