github.com/dpiddy/docker@v1.12.2-rc1/docs/breaking_changes.md (about)

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     3  aliases = ["/engine/misc/breaking/"]
     4  title = "Breaking changes"
     5  description = "Breaking changes"
     6  keywords = ["docker, documentation, about, technology, breaking",
     7  "incompatibilities"]
     8  [menu.main]
     9  parent = "engine_use"
    10  weight=80
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    12  <![end-metadata]-->
    13  
    14  # Breaking changes and incompatibilities
    15  
    16  Every Engine release strives to be backward compatible with its predecessors.
    17  In all cases, the policy is that feature removal is communicated two releases
    18  in advance and documented as part of the [deprecated features](deprecated.md)
    19  page.
    20  
    21  Unfortunately, Docker is a fast moving project, and newly introduced features
    22  may sometime introduce breaking changes and/or incompatibilities. This page
    23  documents these by Engine version.
    24  
    25  # Engine 1.12
    26  
    27  Docker clients <= 1.9.2 used an invalid Host header when making request to the
    28  daemon. Docker 1.12 is built using golang 1.6 which is now checking the validity
    29  of the Host header and as such clients <= 1.9.2 can't talk anymore to the daemon. 
    30  [An environment variable was added to overcome this issue.](reference/commandline/dockerd.md#miscellaneous-options)
    31  
    32  # Engine 1.10
    33  
    34  There were two breaking changes in the 1.10 release.
    35  
    36  ## Registry
    37  
    38  Registry 2.3 includes improvements to the image manifest that have caused a
    39  breaking change. Images pushed by Engine 1.10 to a Registry 2.3 cannot be
    40  pulled by digest by older Engine versions. A `docker pull` that encounters this
    41  situation returns the following error:
    42  
    43  ```
    44   Error response from daemon: unsupported schema version 2 for tag TAGNAME
    45  ```
    46  
    47  Docker Content Trust heavily relies on pull by digest. As a result, images
    48  pushed from the Engine 1.10 CLI to a 2.3 Registry cannot be pulled by older
    49  Engine CLIs (< 1.10) with Docker Content Trust enabled.
    50  
    51  If you are using an older Registry version (< 2.3), this problem does not occur
    52  with any version of the Engine CLI; push, pull, with and without content trust
    53  work as you would expect.
    54  
    55  ## Docker Content Trust
    56  
    57  Engine older than the current 1.10 cannot pull images from repositories that
    58  have enabled key delegation. Key delegation is a feature which requires a
    59  manual action to enable.