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metadata: define content sharing policy

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This changeset modifies the metadata store to allow one to set a
"content sharing policy" that defines how blobs are shared between
namespaces in the content store.

The default mode "shared" will make blobs available in all namespaces
once it is pulled into any namespace.  The blob will be pulled into
the namespace if a writer is opened with the "Expected" digest that
is already present in the backend.

The alternative mode, "isolated" requires that clients prove they have
access to the content by providing all of the content to the ingest
before the blob is added to the namespace.

Both modes share backing data, while "shared" will reduce total
bandwidth across namespaces, at the cost of allowing access to any
blob just by knowing its digest.

Note: Most functional codes and changelog of this commit originate from
Stephen J Day <stephen.day@docker.com>, see
40455aade8

Fixes #1713 Fixes #2865

Signed-off-by: Eric Lin <linxiulei@gmail.com>
This commit is contained in:
Eric Lin
2018-12-18 15:45:39 +08:00
committed by leilei.lin
parent cc06a65a79
commit 4247f2684d
7 changed files with 221 additions and 20 deletions
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docs/ops.md
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@@ -220,3 +220,21 @@ The linux runtime allows a few options to be set to configure the shim and the r
# (this only need to be set on kernel < 3.18)
shim_no_newns = true
```
### Bolt Metadata Plugin
The bolt metadata plugin allows configuration of the content sharing policy between namespaces.
The default mode "shared" will make blobs available in all namespaces once it is pulled into any namespace.
The blob will be pulled into the namespace if a writer is opened with the "Expected" digest that is already present in the backend.
The alternative mode, "isolated" requires that clients prove they have access to the content by providing all of the content to the ingest before the blob is added to the namespace.
Both modes share backing data, while "shared" will reduce total bandwidth across namespaces, at the cost of allowing access to any blob just by knowing its digest.
The default is "shared". While this is largely the most desired policy, one can change to "isolated" mode with the following configuration:
```toml
[plugins.bolt]
content_sharing_policy = "isolated"
```