85 lines
3.3 KiB
Markdown
85 lines
3.3 KiB
Markdown
<!--[metadata]>
|
|
+++
|
|
title = "Compatibility"
|
|
description = "describes get by digest pitfall"
|
|
keywords = ["registry, manifest, images, tags, repository, distribution, digest"]
|
|
[menu.main]
|
|
parent="smn_registry_ref"
|
|
weight=9
|
|
+++
|
|
<![end-metadata]-->
|
|
|
|
# Registry Compatibility
|
|
|
|
## Synopsis
|
|
*If a manifest is pulled by _digest_ from a registry 2.3 with Docker Engine 1.9
|
|
and older, and the manifest was pushed with Docker Engine 1.10, a security check
|
|
will cause the Engine to receive a manifest it cannot use and the pull will fail.*
|
|
|
|
## Registry Manifest Support
|
|
|
|
Historically, the registry has supported a [single manifest type](./spec/manifest-v2-1.md)
|
|
known as _Schema 1_.
|
|
|
|
With the move toward multiple architecture images the distribution project
|
|
introduced two new manifest types: Schema 2 manifests and manifest lists. The
|
|
registry 2.3 supports all three manifest types and in order to be compatible
|
|
with older Docker engines will, in certain cases, do an on-the-fly
|
|
transformation of a manifest before serving the JSON in the response.
|
|
|
|
This conversion has some implications for pulling manifests by digest and this
|
|
document enumerate these implications.
|
|
|
|
|
|
## Content Addressable Storage (CAS)
|
|
|
|
Manifests are stored and retrieved in the registry by keying off a digest
|
|
representing a hash of the contents. One of the advantages provided by CAS is
|
|
security: if the contents are changed, then the digest will no longer match.
|
|
This prevents any modification of the manifest by a MITM attack or an untrusted
|
|
third party.
|
|
|
|
When a manifest is stored by the registry, this digest is returned in the HTTP
|
|
response headers and, if events are configured, delivered within the event. The
|
|
manifest can either be retrieved by the tag, or this digest.
|
|
|
|
For registry versions 2.2.1 and below, the registry will always store and
|
|
serve _Schema 1_ manifests. The Docker Engine 1.10 will first
|
|
attempt to send a _Schema 2_ manifest, falling back to sending a
|
|
Schema 1 type manifest when it detects that the registry does not
|
|
support the new version.
|
|
|
|
|
|
## Registry v2.3
|
|
|
|
### Manifest Push with Docker 1.9 and Older
|
|
|
|
The Docker Engine will construct a _Schema 1_ manifest which the
|
|
registry will persist to disk.
|
|
|
|
When the manifest is pulled by digest or tag with any docker version, a
|
|
_Schema 1_ manifest will be returned.
|
|
|
|
### Manifest Push with Docker 1.10
|
|
|
|
The docker engine will construct a _Schema 2_ manifest which the
|
|
registry will persist to disk.
|
|
|
|
When the manifest is pulled by digest or tag with Docker Engine 1.10, a
|
|
_Schema 2_ manifest will be returned. The Docker Engine 1.10
|
|
understands the new manifest format.
|
|
|
|
When the manifest is pulled by *tag* with Docker Engine 1.9 and older, the
|
|
manifest is converted on-the-fly to _Schema 1_ and sent in the
|
|
response. The Docker Engine 1.9 is compatible with this older format.
|
|
|
|
*When the manifest is pulled by _digest_ with Docker Engine 1.9 and older, the
|
|
same rewriting process will not happen in the registry. If this were to happen
|
|
the digest would no longer match the hash of the manifest and would violate the
|
|
constraints of CAS.*
|
|
|
|
For this reason if a manifest is pulled by _digest_ from a registry 2.3 with Docker
|
|
Engine 1.9 and older, and the manifest was pushed with Docker Engine 1.10, a
|
|
security check will cause the Engine to receive a manifest it cannot use and the
|
|
pull will fail.
|