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What is the difference between Nova metadata service and Heat metadata server?

asked 2015-02-13 04:26:03 -0500

kevin_zhu gravatar image

I want to know what is the difference of them from function perspective and also the difference in terms of what content is stored for each part.

Thanks in advance for that!

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answered 2015-02-15 09:18:18 -0500

Metadata service serves instance-specific-data to other services(specially nova and heat). There are two main types of instance-specific data:

  • Instance Metadata: Mainly consumed by compute service(Nova, instances)
  • User data: Mainly consumed by heat(and other cloud aware agents such as cloud-init)

Both heat and nova use metadata service for different purposes, which both are compared side to side in the following:

From Nova point of view

  • Purpose: From this perspective the primary goal of metedata service is to serve instance metadata.
  • Content: Instance metadata that includes but not limmited to:
  • instance-id
  • instance-type
  • kernel-id
  • local-hostname
  • public-hostname
  • ramdisk-id

From Heat Point of view

  • Purpose: Heat can be configured to use matadata service to pass user's data(e.g. instance root password) to the created instance at instance initialization state. Also Heat connect to metadata service in order to get notified about any events(e.g. intstance failure or metadata changes). In more detail, cf-engine monitors the instance metadata and executes hooks when the metadata changes(I don't really know this last feature is implemented or not. I think this is a blueprint).
  • Content: The primary content is User's data that incldues but not limmited to
    • instance root password
    • startup script

Hope to be useful.

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Thank you, Mzoorikh. That is very helpful.

kevin_zhu gravatar imagekevin_zhu ( 2015-03-07 21:53:04 -0500 )edit

One more, Mzoorikh do you have some insight for this?

https://ask.openstack.org/en/question...

kevin_zhu gravatar imagekevin_zhu ( 2015-03-07 21:59:48 -0500 )edit
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answered 2015-02-15 07:58:31 -0500

Qiming gravatar image

Heat metadata service is provided via the CFN API, its primary use is for heat-cfntools to talk to Heat via that API. Nova metadata service is completely different, with its use mainly targeted at OpenStack services.

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Tengqim, thanks. So in terms of Heat, its metadata service is ONLY provided through heat-cfn-api but not heat api, right?

kevin_zhu gravatar imagekevin_zhu ( 2015-03-07 21:55:34 -0500 )edit

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Asked: 2015-02-13 04:26:03 -0500

Seen: 4,293 times

Last updated: Feb 15 '15