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Diffstat (limited to 'doc/source/admin/how_it_works.rst')
| -rw-r--r-- | doc/source/admin/how_it_works.rst | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/doc/source/admin/how_it_works.rst b/doc/source/admin/how_it_works.rst index 5f4a6773..20a5f477 100644 --- a/doc/source/admin/how_it_works.rst +++ b/doc/source/admin/how_it_works.rst @@ -223,3 +223,36 @@ fields: .. note:: This is most likely to be set by the DHCP server. Could be localhost if the DHCP server does not set it. + +Image Checksums +--------------- + +As part of the process of downloading images to be written to disk as part of +image deployment, a series of fields are utilized to determine if the +image which has been downloaded matches what the user stated as the expected +image checksum utilizing the ``instance_info/image_checksum`` value. + +OpenStack, as a whole, has replaced the "legacy" ``checksum`` field with +``os_hash_value`` and ``os_hash_algo`` fields, which allows for an image +checksum and value to be asserted. An advantage of this is a variety of +algorithms are available, if a user/operator is so-inclined. + +For the purposes of Ironic, we continue to support the pass-through checksum +field as we support the checksum being retrieved via a URL. + +We also support determining the checksum by length. + +The field can be utilized to designate: + +* A URL to retreive a checksum from. +* MD5 (Disabled by default, see ``[DEFAULT]md5_enabled`` in the agent + configuration file.) +* SHA-2 based SHA256 +* SHA-2 based SHA512 + +SHA-3 based checksums are not supported for auto-determination as they can +have a variable length checksum result. At of when this documentation was +added, SHA-2 based checksum algorithms have not been withdrawn from from +approval. If you need to force use of SHA-3 based checksums, you *must* +utilize the ``os_hash_algo`` setting along with the ``os_hash_value`` +setting. |