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docker-patcher

docker-patcher provides a cli & API to calculate and apply binary diffs against Docker images. Diffing is done using bsdiff/bspatch, wrapped nicely by @icedream/go-bsdiff.

While binary patching might not be particularly useful in traditional datacenter/server environments, it can be very beneficial for devices with limited internet connectivity (e.g. IoT/M2M).

Warning: Work In Progress

The CLI has some rough edges. The package's main API was broken to make it easier to include in other projects.

Usage

Setup

$ go build -o bin/didiff ./cmd/didiff

Extra: temporarily add these tools to your path

$ export PATH=$PATH:`pwd`/bin

Create a patch

didiff create sha256:original_docker_image sha256:new_docker_image /path/to/diff.patch

Apply a patch

didiff apply sha256:original_docker_image sha256:new_docker_image /path/to/diff.patch

didiff apply accepts an optional -t argument, specifying the a repo:tag to be applied to the new image, once loaded. This is optional.

Example

In this example we'll create a patch to upgrade from nginx:1.15.11 to nginx:1.15.12.

Create a patch

To create the patch, ensure you have both the old and new images available:

$ docker images --no-trunc
REPOSITORY  TAG         IMAGE ID                                                                  CREATED       SIZE
nginx       1.15.11     sha256:bb776ce48575796501bcc53e511563116132b789ab0552d520513da8c738cba2   12 days ago   109MB
nginx       1.15.12     sha256:27a188018e1847b312022b02146bb7ac3da54e96fab838b7db9f102c8c3dd778   6 days ago    109MB

The shortened image IDs for 1.15.11 and 1.15.12 are bb776ce48575 and 27a188018e18, respectively.

didiff create bb776ce48575 27a188018e18 `pwd`/nginx_1-15-11_to_1-15-12.patch # Using full length IDs is supported, too

After a few seconds (or minutes, depending :)) the patch will be written to nginx_1-15-1_to_1-15-12.patch.

Upon inspecting the patch, we can see that in this case we're weighing in under 300KB! That's much better than a ~23MB pull (assuming caching).

$ du -hs ./nginx_1-15-11_to_1-15-12.patch
260K    ./nginx_1-15-11_to_1-15-12.patch

Apply a patch

Applying the patch takes similar motions. If you're testing this out on a machine with the old and new images, you can easily remove an image with docker rmi your_img_id_here

Ensure the image doesn't exist locally:

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               1.15.11             bb776ce48575        12 days ago         109MB

Now we can use the use the patch we built previously. Specifying -t ensures that the new image is properly re-tagged.

./didiff apply bb776ce48575 27a188018e18 `pwd`/nginx_1-15-11_to_1-15-12.patch -t nginx:1.15.12

We can see the image was patched and loaded by running docker images

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               1.15.12             27a188018e18        6 days ago          109MB
nginx               1.15.11             bb776ce48575        12 days ago         109MB

As a final step, for good measure, let's verify the new image works!

$ docker run --rm -d \
    --name docker-patch-test \
    -p 8080:80 27a188018e18 \
    && curl -sSL -D - localhost:8080 -o /dev/null | grep Server: \
    && docker kill docker-patch-test

The above command should have printed (among other things!) Server: nginx/1.15.12, indicating success!

Something is broken/could be better/etc...

Please feel free to open PRs, Issues, or send me an email!