Docker 29 Images aren't compressed after squash

[lorenz-werner]

When I squash images built with Docker 29, those images are bigger than before, because it seems like they are no longer compressed.
This is problematic, because those images aren't working with JIB and well, they are bigger.

With docker 29+ squashing won't work as expected:

--- docker version ---
Client:
 Version:           29.0.4
 API version:       1.52
 Go version:        go1.25.4
 Git commit:        3247a5a
 Built:             Mon Nov 24 21:58:38 2025
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          29.0.4
  API version:      1.52 (minimum version 1.44)
  Go version:       go1.25.4
  Git commit:       4612690e
  Built:            Mon Nov 24 22:01:10 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v2.1.5
  GitCommit:        fcd43222d6b07379a4be9786bda52438f0dd16a1
 runc:
  Version:          1.3.3
  GitCommit:        v1.3.3-0-gd842d77
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

--- build original image ---
#0 building with "default" instance using docker driver

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 69B done
#1 DONE 0.0s

#2 [internal] load metadata for docker.io/library/debian:latest
#2 DONE 0.9s

#3 [internal] load .dockerignore
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [1/2] FROM docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed
#4 resolve docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 0.0s done
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0B / 49.30MB 0.2s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 15.73MB / 49.30MB 0.5s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 31.46MB / 49.30MB 0.6s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 40.89MB / 49.30MB 0.8s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 49.30MB / 49.30MB 0.9s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 49.30MB / 49.30MB 0.9s done
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0.4s done
#4 DONE 1.4s

#5 [2/2] RUN echo foo > /bar
#5 DONE 0.4s

#6 exporting to image
#6 exporting layers 0.1s done
#6 exporting manifest sha256:8a36237b0b1053059f573eab5456a22f5b7660b101a7b8f40355987f5878b4aa 0.0s done
#6 exporting config sha256:a3059884c168e6bb512861ebd80166163e27db341c48a1e2f684bfbc40a3e34f 0.0s done
#6 naming to docker.io/library/foo:latest done
#6 unpacking to docker.io/library/foo:latest 0.0s done
#6 DONE 0.1s

--- squash image ---
2026-04-20 13:37:52,238 squash.py:54         INFO  docker-squash version 1.2.2, Docker 29.0.4, API 1.52...
2026-04-20 13:37:52,238 squash.py:96         INFO  Using v2 image format
2026-04-20 13:37:52,244 image.py:179        INFO  Old image has 2 layers
2026-04-20 13:37:52,244 image.py:212        INFO  Checking if squashing is necessary...
2026-04-20 13:37:52,244 image.py:224        INFO  Attempting to squash last 2 layers...
2026-04-20 13:37:52,244 image.py:372        INFO  Saving image sha256:8a36237b0b1053059f573eab5456a22f5b7660b101a7b8f40355987f5878b4aa to /tmp/docker-squash-inep5mk5/old directory...
2026-04-20 13:37:52,473 image.py:407        INFO  Image saved!
2026-04-20 13:37:52,473 image.py:233        INFO  Squashing image 'foo'...
2026-04-20 13:37:52,474 image.py:750        INFO  Starting squashing for /tmp/docker-squash-inep5mk5/new/squashed/layer.tar...
2026-04-20 13:37:52,474 image.py:775        INFO  Squashing file '/tmp/docker-squash-inep5mk5/old/blobs/sha256/baa5fc1c2fcd86eb46a5356d9e93a5edbd10ae0b1e5df4811311a494f69cb554'...
2026-04-20 13:37:52,474 image.py:775        INFO  Squashing file '/tmp/docker-squash-inep5mk5/old/blobs/sha256/a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155'...
2026-04-20 13:37:53,801 image.py:923        INFO  Squashing finished!
2026-04-20 13:37:53,874 image.py:245        INFO  Original image size: 47.02 MB
2026-04-20 13:37:53,874 image.py:246        INFO  Squashed image size: 118.10 MB
2026-04-20 13:37:53,874 image.py:249        INFO  If the squashed image is larger than original it means that there were no meaningful files to squash and it just added metadata. Are you sure you specified correct parameters?
2026-04-20 13:37:53,874 squash.py:136        INFO  New squashed image ID is c64188825f55ff7381844dcf5bc80eaed885131395c8d66d234c02148d7628bc
2026-04-20 13:37:54,809 image.py:281        INFO  Image registered in Docker daemon as foo:squashed
2026-04-20 13:37:54,813 squash.py:159        INFO  Done

--- original manifest ---
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "digest": "sha256:a3059884c168e6bb512861ebd80166163e27db341c48a1e2f684bfbc40a3e34f",
    "size": 660
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "digest": "sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155",
      "size": 49297833
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "digest": "sha256:baa5fc1c2fcd86eb46a5356d9e93a5edbd10ae0b1e5df4811311a494f69cb554",
      "size": 104
    }
  ]
}

--- squashed manifest ---
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "digest": "sha256:c64188825f55ff7381844dcf5bc80eaed885131395c8d66d234c02148d7628bc",
    "size": 372
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar",
      "digest": "sha256:ade72a6b4d581e45e5affdc9269f55ebd5e8bfad11a335985fa2209e4eee73dd",
      "size": 123832320
    }
  ]
}

--- original layer mediaTypes ---
application/vnd.docker.image.rootfs.diff.tar.gzip
application/vnd.docker.image.rootfs.diff.tar.gzip

--- squashed layer mediaTypes ---
application/vnd.docker.image.rootfs.diff.tar

--- image sizes ---
foo:squashed    554cc145f4cd    258MB
foo:latest      8a36237b0b10    183MB

Here you can see, that the mediaType after squashing is application/vnd.docker.image.rootfs.diff.tar, while it should be application/vnd.docker.image.rootfs.diff.tar.gzip.

And with docker 28.* it works as expected:

--- docker version ---
Client:
 Version:           28.5.2
 API version:       1.51
 Go version:        go1.25.3
 Git commit:        ecc6942
 Built:             Wed Nov  5 14:42:42 2025
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          28.5.2
  API version:      1.51 (minimum version 1.24)
  Go version:       go1.24.9
  Git commit:       89c5e8f
  Built:            Wed Nov  5 14:45:42 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v1.7.28
  GitCommit:        b98a3aace656320842a23f4a392a33f46af97866
 runc:
  Version:          1.3.3
  GitCommit:        v1.3.3-0-gd842d77
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

--- build original image ---
#0 building with "default" instance using docker driver

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 69B done
#1 DONE 0.0s

#2 [internal] load metadata for docker.io/library/debian:latest
#2 DONE 1.1s

#3 [internal] load .dockerignore
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [1/2] FROM docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed
#4 resolve docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 0.0s done
#4 sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 8.93kB / 8.93kB done
#4 sha256:84cc642701b773b0df5a98553f4bf9aab4ad4d10a34c406e46d33ee1fd548fa7 1.02kB / 1.02kB done
#4 sha256:8ce2894044f6727bb22b6a00b3fdb8c345f1e16f2bd8e512e2ecf05d6b8ddd5c 451B / 451B done
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0B / 49.30MB 0.1s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 9.44MB / 49.30MB 0.4s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 13.63MB / 49.30MB 0.6s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 20.97MB / 49.30MB 0.7s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 30.41MB / 49.30MB 0.9s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 48.23MB / 49.30MB 1.1s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 49.30MB / 49.30MB 1.3s done
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0.1s
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0.4s done
#4 DONE 1.8s

#5 [2/2] RUN echo foo > /bar
#5 DONE 0.6s

#6 exporting to image
#6 exporting layers 0.0s done
#6 writing image sha256:bbb0cae47d672e4ae9c45ed5df8a89492f4a68c62de057c93f05d1f225c566f9 done
#6 naming to docker.io/library/foo done
#6 DONE 0.0s

--- squash image ---
2026-04-20 13:38:17,163 squash.py:54         INFO  docker-squash version 1.2.2, Docker 28.5.2, API 1.51...
2026-04-20 13:38:17,164 squash.py:96         INFO  Using v2 image format
2026-04-20 13:38:17,165 image.py:179        INFO  Old image has 2 layers
2026-04-20 13:38:17,165 image.py:212        INFO  Checking if squashing is necessary...
2026-04-20 13:38:17,165 image.py:224        INFO  Attempting to squash last 2 layers...
2026-04-20 13:38:17,165 image.py:372        INFO  Saving image sha256:bbb0cae47d672e4ae9c45ed5df8a89492f4a68c62de057c93f05d1f225c566f9 to /tmp/docker-squash-7gk07c21/old directory...
2026-04-20 13:38:17,866 image.py:407        INFO  Image saved!
2026-04-20 13:38:17,867 image.py:233        INFO  Squashing image 'foo'...
2026-04-20 13:38:17,867 image.py:750        INFO  Starting squashing for /tmp/docker-squash-7gk07c21/new/squashed/layer.tar...
2026-04-20 13:38:17,867 image.py:775        INFO  Squashing file '/tmp/docker-squash-7gk07c21/old/blobs/sha256/759d69e2f182ca5fd107982a72e603f3c9572c2c8674fd4c44e6c87ad52e7e8a'...
2026-04-20 13:38:17,868 image.py:775        INFO  Squashing file '/tmp/docker-squash-7gk07c21/old/blobs/sha256/47e673e32817fbaf53619364587ebf6b2d41f3fd5e02b3fa6a3b2fd01b47ddfb'...
2026-04-20 13:38:18,421 image.py:923        INFO  Squashing finished!
2026-04-20 13:38:18,497 image.py:245        INFO  Original image size: 118.10 MB
2026-04-20 13:38:18,498 image.py:246        INFO  Squashed image size: 118.10 MB
2026-04-20 13:38:18,498 image.py:253        INFO  Image size decreased by 0.00 %
2026-04-20 13:38:18,498 squash.py:136        INFO  New squashed image ID is 9c3b839554b0983a10eb17d44c449ff609ca4a32bddfb28995acb865bde66d1c
2026-04-20 13:38:18,940 image.py:281        INFO  Image registered in Docker daemon as foo:squashed
2026-04-20 13:38:18,944 squash.py:159        INFO  Done

--- original manifest ---
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "size": 660,
    "digest": "sha256:bbb0cae47d672e4ae9c45ed5df8a89492f4a68c62de057c93f05d1f225c566f9"
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 50483003,
      "digest": "sha256:e1d3d3808b7cc00ad2139fd148f20871698ae08d4b95020b8137bd3b7b9b75d4"
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 133,
      "digest": "sha256:2d1db21fec235d9d4c4fc8b32c94f325e0f69af10edc5b516eb9f47a494c4afb"
    }
  ]
}

--- squashed manifest ---
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "size": 372,
    "digest": "sha256:9c3b839554b0983a10eb17d44c449ff609ca4a32bddfb28995acb865bde66d1c"
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 50467368,
      "digest": "sha256:9e50fa3cd8bd823f19b802eb87441112cfd0efb95d4f9cb0f5d8406a79c9ecd2"
    }
  ]
}

--- original layer mediaTypes ---
application/vnd.docker.image.rootfs.diff.tar.gzip
application/vnd.docker.image.rootfs.diff.tar.gzip

--- squashed layer mediaTypes ---
application/vnd.docker.image.rootfs.diff.tar.gzip

--- image sizes ---
foo:squashed    9c3b839554b0    120MB
foo:latest      bbb0cae47d67    120MB

I also tested

• Docker 29.4.0
• docker-squash git master (shows up as 1.3.0)

which are the latest releases and the problem occurs there also.

Is there a known way to get docker-squash working with Docker 29?

[lorenz-werner]

Here are some more logs including commands to reproduce:

============================================================
Testing docker:29.4.0-dind
============================================================
+ apk add --no-cache python3 py3-pip jq
+ python3 -m venv /venv
+ /venv/bin/pip install --no-cache-dir -q 'docker-squash==1.2.2'

[notice] A new release of pip is available: 25.0.1 -> 26.0.1
[notice] To update, run: python3 -m pip install --upgrade pip
+ docker rm -f registry
+ docker run -d -p 5000:5000 --name registry registry:2
Unable to find image 'registry:2' locally
2: Pulling from library/registry
6d464ea18732: Pulling fs layer
bbbdd6c6894b: Pulling fs layer
44cf07d57ee4: Pulling fs layer
3493bf46cdec: Pulling fs layer
8e82f80af0de: Pulling fs layer
b537bf6d1146: Download complete
6d464ea18732: Download complete
32a76c78501f: Download complete
bbbdd6c6894b: Download complete
3493bf46cdec: Download complete
44cf07d57ee4: Download complete
8e82f80af0de: Download complete
bbbdd6c6894b: Pull complete
44cf07d57ee4: Pull complete
8e82f80af0de: Pull complete
6d464ea18732: Pull complete
3493bf46cdec: Pull complete
Digest: sha256:a3d8aaa63ed8681a604f1dea0aa03f100d5895b6a58ace528858a7b332415373
Status: Downloaded newer image for registry:2

--- docker version ---
+ echo
+ echo '--- docker version ---'
+ docker version
Client:
 Version:           29.4.0
 API version:       1.54
 Go version:        go1.26.1
 Git commit:        9d7ad9f
 Built:             Tue Apr  7 08:34:33 2026
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          29.4.0
  API version:      1.54 (minimum version 1.40)
  Go version:       go1.26.1
  Git commit:       daa0cb7f
  Built:            Tue Apr  7 08:36:58 2026
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v2.2.2
  GitCommit:        301b2dac98f15c27117da5c8af12118a041a31d9
 runc:
  Version:          1.3.5
  GitCommit:        v1.3.5-0-g488fc13
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0
+ echo
+ echo '--- build original image ---'
+ docker build '--provenance=false' '--sbom=false' -t foo /work

--- build original image ---
#0 building with "default" instance using docker driver

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 69B done
#1 DONE 0.0s

#2 [internal] load metadata for docker.io/library/debian:latest
#2 DONE 0.9s

#3 [internal] load .dockerignore
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [1/2] FROM docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed
#4 resolve docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 0.0s done
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0B / 49.30MB 0.2s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 4.19MB / 49.30MB 0.5s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 11.53MB / 49.30MB 0.6s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 17.83MB / 49.30MB 0.8s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 23.07MB / 49.30MB 0.9s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 29.36MB / 49.30MB 1.2s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 34.60MB / 49.30MB 1.5s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 39.85MB / 49.30MB 1.7s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 44.04MB / 49.30MB 1.8s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 47.19MB / 49.30MB 2.0s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 49.30MB / 49.30MB 2.1s done
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0.4s done
#4 DONE 2.5s

#5 [2/2] RUN echo foo > /bar
#5 DONE 0.5s

#6 exporting to image
#6 exporting layers 0.0s done
#6 exporting manifest sha256:9ed006dbd572f769d0b27e88111a0f6739ccae9410d73e405ef55bb55a9ac454 done
#6 exporting config sha256:eb3a666c6fc50edab4289e225c15398082a7b506b5c6c62b3ff31d5b6289e82b done
#6 naming to docker.io/library/foo:latest done
#6 unpacking to docker.io/library/foo:latest 0.0s done
#6 DONE 0.1s
+ echo
+ echo '--- squash image ---'
+ /venv/bin/docker-squash foo -t foo:squashed

--- squash image ---
2026-04-20 13:48:27,039 squash.py:54         INFO  docker-squash version 1.2.2, Docker 29.4.0, API 1.54...
2026-04-20 13:48:27,039 squash.py:96         INFO  Using v2 image format
2026-04-20 13:48:27,046 image.py:179        INFO  Old image has 2 layers
2026-04-20 13:48:27,046 image.py:212        INFO  Checking if squashing is necessary...
2026-04-20 13:48:27,046 image.py:224        INFO  Attempting to squash last 2 layers...
2026-04-20 13:48:27,046 image.py:372        INFO  Saving image sha256:9ed006dbd572f769d0b27e88111a0f6739ccae9410d73e405ef55bb55a9ac454 to /tmp/docker-squash-yf0ii_60/old directory...
2026-04-20 13:48:27,260 image.py:407        INFO  Image saved!
2026-04-20 13:48:27,260 image.py:233        INFO  Squashing image 'foo'...
2026-04-20 13:48:27,260 image.py:750        INFO  Starting squashing for /tmp/docker-squash-yf0ii_60/new/squashed/layer.tar...
2026-04-20 13:48:27,260 image.py:775        INFO  Squashing file '/tmp/docker-squash-yf0ii_60/old/blobs/sha256/bb43299d0ae694a9b87a685aa6682a22c1a74e1d52fabd31ecf082ed403ae50c'...
2026-04-20 13:48:27,261 image.py:775        INFO  Squashing file '/tmp/docker-squash-yf0ii_60/old/blobs/sha256/a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155'...
2026-04-20 13:48:28,568 image.py:923        INFO  Squashing finished!
2026-04-20 13:48:28,643 image.py:245        INFO  Original image size: 47.02 MB
2026-04-20 13:48:28,643 image.py:246        INFO  Squashed image size: 118.10 MB
2026-04-20 13:48:28,643 image.py:249        INFO  If the squashed image is larger than original it means that there were no meaningful files to squash and it just added metadata. Are you sure you specified correct parameters?
2026-04-20 13:48:28,643 squash.py:136        INFO  New squashed image ID is eb9514189061f4ffbaabf1e99d074639205cb759af9febedceb2fcee704d2fb8
2026-04-20 13:48:29,331 image.py:281        INFO  Image registered in Docker daemon as foo:squashed
2026-04-20 13:48:29,336 squash.py:159        INFO  Done

--- tag + push original ---
+ echo
+ echo '--- tag + push original ---'
+ docker tag foo localhost:5000/foo:orig
+ docker push localhost:5000/foo:orig
+ echo
+ echo '--- tag + push squashed ---'
+ docker tag foo:squashed localhost:5000/foo:squashed

--- tag + push squashed ---
+ docker push localhost:5000/foo:squashed
+ echo
+ echo '--- original manifest ---'

--- original manifest ---
+ docker manifest inspect --insecure localhost:5000/foo:orig
+ jq
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "digest": "sha256:eb3a666c6fc50edab4289e225c15398082a7b506b5c6c62b3ff31d5b6289e82b",
    "size": 660
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "digest": "sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155",
      "size": 49297833
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "digest": "sha256:bb43299d0ae694a9b87a685aa6682a22c1a74e1d52fabd31ecf082ed403ae50c",
      "size": 105
    }
  ]
}
+ echo
+ echo '--- squashed manifest ---'

--- squashed manifest ---
+ docker manifest inspect --insecure localhost:5000/foo:squashed
+ jq
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "digest": "sha256:eb9514189061f4ffbaabf1e99d074639205cb759af9febedceb2fcee704d2fb8",
    "size": 372
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar",
      "digest": "sha256:a7cc3f8f40b8c5c9a778ce1c05a4cd169d72894fdc4106764dfbc2fc202c5670",
      "size": 123832320
    }
  ]
}
+ echo
+ echo '--- original layer mediaTypes ---'

--- original layer mediaTypes ---
+ docker manifest inspect --insecure localhost:5000/foo:orig
+ jq -r '.layers[].mediaType // empty'
application/vnd.docker.image.rootfs.diff.tar.gzip
application/vnd.docker.image.rootfs.diff.tar.gzip

--- squashed layer mediaTypes ---
+ echo
+ echo '--- squashed layer mediaTypes ---'
+ docker manifest inspect --insecure localhost:5000/foo:squashed
+ jq -r '.layers[].mediaType // empty'
application/vnd.docker.image.rootfs.diff.tar

+ echo
+ echo '--- image sizes ---'
--- image sizes ---
+ docker images --format '{{.Repository}}:{{.Tag}}\t{{.ID}}\t{{.Size}}'
+ grep ^foo
foo:squashed    14f05520fb55    258MB
foo:latest      9ed006dbd572    183MB

============================================================
Testing docker:29.0.4-dind
============================================================
+ apk add --no-cache python3 py3-pip jq
+ python3 -m venv /venv
+ /venv/bin/pip install --no-cache-dir -q 'docker-squash==1.2.2'

[notice] A new release of pip is available: 25.0.1 -> 26.0.1
[notice] To update, run: python3 -m pip install --upgrade pip
+ docker rm -f registry
+ docker run -d -p 5000:5000 --name registry registry:2
Unable to find image 'registry:2' locally
2: Pulling from library/registry
3493bf46cdec: Pulling fs layer
44cf07d57ee4: Pulling fs layer
8e82f80af0de: Pulling fs layer
bbbdd6c6894b: Pulling fs layer
6d464ea18732: Pulling fs layer
3493bf46cdec: Download complete
6d464ea18732: Download complete
44cf07d57ee4: Download complete
44cf07d57ee4: Pull complete
bbbdd6c6894b: Download complete
bbbdd6c6894b: Pull complete
8e82f80af0de: Download complete
3493bf46cdec: Pull complete
8e82f80af0de: Pull complete
6d464ea18732: Pull complete
Digest: sha256:a3d8aaa63ed8681a604f1dea0aa03f100d5895b6a58ace528858a7b332415373
Status: Downloaded newer image for registry:2
+ echo
+ echo '--- docker version ---'
+ docker version

--- docker version ---
Client:
 Version:           29.0.4
 API version:       1.52
 Go version:        go1.25.4
 Git commit:        3247a5a
 Built:             Mon Nov 24 21:58:38 2025
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          29.0.4
  API version:      1.52 (minimum version 1.44)
  Go version:       go1.25.4
  Git commit:       4612690e
  Built:            Mon Nov 24 22:01:10 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v2.1.5
  GitCommit:        fcd43222d6b07379a4be9786bda52438f0dd16a1
 runc:
  Version:          1.3.3
  GitCommit:        v1.3.3-0-gd842d77
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0
+ echo
+ echo '--- build original image ---'

--- build original image ---
+ docker build '--provenance=false' '--sbom=false' -t foo /work
#0 building with "default" instance using docker driver

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 69B done
#1 DONE 0.0s

#2 [internal] load metadata for docker.io/library/debian:latest
#2 DONE 0.9s

#3 [internal] load .dockerignore
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [1/2] FROM docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed
#4 resolve docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 0.0s done
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0B / 49.30MB 0.2s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 8.39MB / 49.30MB 0.5s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 13.63MB / 49.30MB 0.6s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 26.21MB / 49.30MB 0.8s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 35.65MB / 49.30MB 0.9s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 46.14MB / 49.30MB 1.1s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 49.30MB / 49.30MB 1.2s done
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0.4s done
#4 DONE 1.6s

#5 [2/2] RUN echo foo > /bar
#5 DONE 0.5s

#6 exporting to image
#6 exporting layers 0.0s done
#6 exporting manifest sha256:0f6c67c8cbe2463828a8331c6519a96f2c13d7ed8888038230053a1abc7478a3 done
#6 exporting config sha256:5606e57cb15abdbda6777c20d4efb064b66b92981ff5b15003d831c7e6cfa087 done
#6 naming to docker.io/library/foo:latest done
#6 unpacking to docker.io/library/foo:latest 0.0s done
#6 DONE 0.1s
+ echo
+ echo '--- squash image ---'
+ /venv/bin/docker-squash foo -t foo:squashed

--- squash image ---
2026-04-20 13:48:42,571 squash.py:54         INFO  docker-squash version 1.2.2, Docker 29.0.4, API 1.52...
2026-04-20 13:48:42,571 squash.py:96         INFO  Using v2 image format
2026-04-20 13:48:42,578 image.py:179        INFO  Old image has 2 layers
2026-04-20 13:48:42,578 image.py:212        INFO  Checking if squashing is necessary...
2026-04-20 13:48:42,578 image.py:224        INFO  Attempting to squash last 2 layers...
2026-04-20 13:48:42,578 image.py:372        INFO  Saving image sha256:0f6c67c8cbe2463828a8331c6519a96f2c13d7ed8888038230053a1abc7478a3 to /tmp/docker-squash-1s7sn8k6/old directory...
2026-04-20 13:48:42,804 image.py:407        INFO  Image saved!
2026-04-20 13:48:42,804 image.py:233        INFO  Squashing image 'foo'...
2026-04-20 13:48:42,804 image.py:750        INFO  Starting squashing for /tmp/docker-squash-1s7sn8k6/new/squashed/layer.tar...
2026-04-20 13:48:42,804 image.py:775        INFO  Squashing file '/tmp/docker-squash-1s7sn8k6/old/blobs/sha256/3f54267494ee4ec0344755ca00760809acf9ec36af97f959deced69fab235c23'...
2026-04-20 13:48:42,805 image.py:775        INFO  Squashing file '/tmp/docker-squash-1s7sn8k6/old/blobs/sha256/a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155'...
2026-04-20 13:48:44,131 image.py:923        INFO  Squashing finished!
2026-04-20 13:48:44,217 image.py:245        INFO  Original image size: 47.02 MB
2026-04-20 13:48:44,217 image.py:246        INFO  Squashed image size: 118.10 MB
2026-04-20 13:48:44,217 image.py:249        INFO  If the squashed image is larger than original it means that there were no meaningful files to squash and it just added metadata. Are you sure you specified correct parameters?
2026-04-20 13:48:44,217 squash.py:136        INFO  New squashed image ID is 2d8e5cbffdf439ef187010983b6f243bbb3095a6779e397db63970e80ed185b4
2026-04-20 13:48:44,858 image.py:281        INFO  Image registered in Docker daemon as foo:squashed
2026-04-20 13:48:44,862 squash.py:159        INFO  Done

--- tag + push original ---
+ echo
+ echo '--- tag + push original ---'
+ docker tag foo localhost:5000/foo:orig
+ docker push localhost:5000/foo:orig
+ echo
+ echo '--- tag + push squashed ---'
+ docker tag foo:squashed localhost:5000/foo:squashed

--- tag + push squashed ---
+ docker push localhost:5000/foo:squashed
+ echo
+ echo '--- original manifest ---'

--- original manifest ---
+ docker manifest inspect --insecure localhost:5000/foo:orig
+ jq
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "digest": "sha256:5606e57cb15abdbda6777c20d4efb064b66b92981ff5b15003d831c7e6cfa087",
    "size": 660
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "digest": "sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155",
      "size": 49297833
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "digest": "sha256:3f54267494ee4ec0344755ca00760809acf9ec36af97f959deced69fab235c23",
      "size": 105
    }
  ]
}

--- squashed manifest ---
+ echo
+ echo '--- squashed manifest ---'
+ docker manifest inspect --insecure localhost:5000/foo:squashed
+ jq
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "digest": "sha256:2d8e5cbffdf439ef187010983b6f243bbb3095a6779e397db63970e80ed185b4",
    "size": 372
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar",
      "digest": "sha256:ed96f32ff8e9e5a10be1129705f0993000be2b1c951bf95050e7c28c7abf1de4",
      "size": 123832320
    }
  ]
}
+ echo
+ echo '--- original layer mediaTypes ---'

--- original layer mediaTypes ---
+ docker manifest inspect --insecure localhost:5000/foo:orig
+ jq -r '.layers[].mediaType // empty'
application/vnd.docker.image.rootfs.diff.tar.gzip
application/vnd.docker.image.rootfs.diff.tar.gzip
+ echo
+ echo '--- squashed layer mediaTypes ---'

--- squashed layer mediaTypes ---
+ docker manifest inspect --insecure localhost:5000/foo:squashed
+ jq -r '.layers[].mediaType // empty'
application/vnd.docker.image.rootfs.diff.tar

--- image sizes ---
+ echo
+ echo '--- image sizes ---'
+ docker images --format '{{.Repository}}:{{.Tag}}\t{{.ID}}\t{{.Size}}'
+ grep ^foo
foo:squashed    1aed512216f5    258MB
foo:latest      0f6c67c8cbe2    183MB

============================================================
Testing docker:28.5.2-dind
============================================================
+ apk add --no-cache python3 py3-pip jq
+ python3 -m venv /venv
+ /venv/bin/pip install --no-cache-dir -q 'docker-squash==1.2.2'

[notice] A new release of pip is available: 25.0.1 -> 26.0.1
[notice] To update, run: python3 -m pip install --upgrade pip
+ docker rm -f registry
+ docker run -d -p 5000:5000 --name registry registry:2
Unable to find image 'registry:2' locally
2: Pulling from library/registry
44cf07d57ee4: Pulling fs layer
bbbdd6c6894b: Pulling fs layer
8e82f80af0de: Pulling fs layer
3493bf46cdec: Pulling fs layer
6d464ea18732: Pulling fs layer
3493bf46cdec: Waiting
6d464ea18732: Waiting
bbbdd6c6894b: Verifying Checksum
bbbdd6c6894b: Download complete
44cf07d57ee4: Verifying Checksum
44cf07d57ee4: Download complete
44cf07d57ee4: Pull complete
bbbdd6c6894b: Pull complete
8e82f80af0de: Verifying Checksum
8e82f80af0de: Download complete
8e82f80af0de: Pull complete
3493bf46cdec: Verifying Checksum
3493bf46cdec: Download complete
3493bf46cdec: Pull complete
6d464ea18732: Pull complete
Digest: sha256:a3d8aaa63ed8681a604f1dea0aa03f100d5895b6a58ace528858a7b332415373
Status: Downloaded newer image for registry:2
+ echo
+ echo '--- docker version ---'
+ docker version

--- docker version ---
Client:
 Version:           28.5.2
 API version:       1.51
 Go version:        go1.25.3
 Git commit:        ecc6942
 Built:             Wed Nov  5 14:42:42 2025
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          28.5.2
  API version:      1.51 (minimum version 1.24)
  Go version:       go1.24.9
  Git commit:       89c5e8f
  Built:            Wed Nov  5 14:45:42 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v1.7.28
  GitCommit:        b98a3aace656320842a23f4a392a33f46af97866
 runc:
  Version:          1.3.3
  GitCommit:        v1.3.3-0-gd842d77
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

--- build original image ---
+ echo
+ echo '--- build original image ---'
+ docker build '--provenance=false' '--sbom=false' -t foo /work
#0 building with "default" instance using docker driver

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 69B done
#1 DONE 0.0s

#2 [internal] load metadata for docker.io/library/debian:latest
#2 DONE 0.9s

#3 [internal] load .dockerignore
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [1/2] FROM docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed
#4 resolve docker.io/library/debian:latest@sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 0.0s done
#4 sha256:3352c2e13876c8a5c5873ef20870e1939e73cb9a3c1aeba5e3e72172a85ce9ed 8.93kB / 8.93kB done
#4 sha256:84cc642701b773b0df5a98553f4bf9aab4ad4d10a34c406e46d33ee1fd548fa7 1.02kB / 1.02kB done
#4 sha256:8ce2894044f6727bb22b6a00b3fdb8c345f1e16f2bd8e512e2ecf05d6b8ddd5c 451B / 451B done
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0B / 49.30MB 0.1s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 9.44MB / 49.30MB 0.4s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 17.83MB / 49.30MB 0.5s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 30.41MB / 49.30MB 0.8s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 37.75MB / 49.30MB 1.0s
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 48.23MB / 49.30MB 1.1s
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155
#4 sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 49.30MB / 49.30MB 1.3s done
#4 extracting sha256:a7730063fcfe708b222d34c4f07d633dfe087a28c05c4daaab2fa9943854c155 0.4s done
#4 DONE 1.8s

#5 [2/2] RUN echo foo > /bar
#5 DONE 0.7s

#6 exporting to image
#6 exporting layers 0.0s done
#6 writing image sha256:b225b0dc0a0e61f7b5489cc2dad81c2372f170d68e71535423eb8f7c067f2e97 done
#6 naming to docker.io/library/foo done
#6 DONE 0.0s
+ echo
+ echo '--- squash image ---'
+ /venv/bin/docker-squash foo -t foo:squashed

--- squash image ---
2026-04-20 13:48:59,239 squash.py:54         INFO  docker-squash version 1.2.2, Docker 28.5.2, API 1.51...
2026-04-20 13:48:59,239 squash.py:96         INFO  Using v2 image format
2026-04-20 13:48:59,241 image.py:179        INFO  Old image has 2 layers
2026-04-20 13:48:59,241 image.py:212        INFO  Checking if squashing is necessary...
2026-04-20 13:48:59,241 image.py:224        INFO  Attempting to squash last 2 layers...
2026-04-20 13:48:59,241 image.py:372        INFO  Saving image sha256:b225b0dc0a0e61f7b5489cc2dad81c2372f170d68e71535423eb8f7c067f2e97 to /tmp/docker-squash-0gspo7ti/old directory...
2026-04-20 13:48:59,976 image.py:407        INFO  Image saved!
2026-04-20 13:48:59,976 image.py:233        INFO  Squashing image 'foo'...
2026-04-20 13:48:59,976 image.py:750        INFO  Starting squashing for /tmp/docker-squash-0gspo7ti/new/squashed/layer.tar...
2026-04-20 13:48:59,976 image.py:775        INFO  Squashing file '/tmp/docker-squash-0gspo7ti/old/blobs/sha256/bf68e3a39befe489e1d510ecc82da47d5a832488beeb9016d2d2903b5a9a2ee6'...
2026-04-20 13:48:59,977 image.py:775        INFO  Squashing file '/tmp/docker-squash-0gspo7ti/old/blobs/sha256/47e673e32817fbaf53619364587ebf6b2d41f3fd5e02b3fa6a3b2fd01b47ddfb'...
2026-04-20 13:49:00,538 image.py:923        INFO  Squashing finished!
2026-04-20 13:49:00,618 image.py:245        INFO  Original image size: 118.10 MB
2026-04-20 13:49:00,618 image.py:246        INFO  Squashed image size: 118.10 MB
2026-04-20 13:49:00,618 image.py:253        INFO  Image size decreased by 0.00 %
2026-04-20 13:49:00,618 squash.py:136        INFO  New squashed image ID is e7ef74c229d77018bc7193b2c54496f9ec2cb8ae3869fdeb14ff09278070b6bc
2026-04-20 13:49:01,090 image.py:281        INFO  Image registered in Docker daemon as foo:squashed
2026-04-20 13:49:01,095 squash.py:159        INFO  Done
+ echo
+ echo '--- tag + push original ---'
+ docker tag foo localhost:5000/foo:orig

--- tag + push original ---
+ docker push localhost:5000/foo:orig
+ echo
+ echo '--- tag + push squashed ---'
+ docker tag foo:squashed localhost:5000/foo:squashed

--- tag + push squashed ---
+ docker push localhost:5000/foo:squashed
+ echo
+ echo '--- original manifest ---'

--- original manifest ---
+ docker manifest inspect --insecure localhost:5000/foo:orig
+ jq
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "size": 660,
    "digest": "sha256:b225b0dc0a0e61f7b5489cc2dad81c2372f170d68e71535423eb8f7c067f2e97"
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 50483003,
      "digest": "sha256:e1d3d3808b7cc00ad2139fd148f20871698ae08d4b95020b8137bd3b7b9b75d4"
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 132,
      "digest": "sha256:35b7c5e829db3b0a77a7309ac212fc67e82e84198ff5da444c38d20b71441929"
    }
  ]
}

--- squashed manifest ---
+ echo
+ echo '--- squashed manifest ---'
+ docker manifest inspect --insecure localhost:5000/foo:squashed
+ jq
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "config": {
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "size": 372,
    "digest": "sha256:e7ef74c229d77018bc7193b2c54496f9ec2cb8ae3869fdeb14ff09278070b6bc"
  },
  "layers": [
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 50467369,
      "digest": "sha256:a330fe1f7e75bf20546d476e805c2515d39f4a5982cb94e6fcc9b11d2fbbd88c"
    }
  ]
}

--- original layer mediaTypes ---
+ echo
+ echo '--- original layer mediaTypes ---'
+ docker manifest inspect --insecure localhost:5000/foo:orig
+ jq -r '.layers[].mediaType // empty'
application/vnd.docker.image.rootfs.diff.tar.gzip
application/vnd.docker.image.rootfs.diff.tar.gzip
+ echo

--- squashed layer mediaTypes ---
+ echo '--- squashed layer mediaTypes ---'
+ docker manifest inspect --insecure localhost:5000/foo:squashed
+ jq -r '.layers[].mediaType // empty'
application/vnd.docker.image.rootfs.diff.tar.gzip
+ echo
+ echo '--- image sizes ---'

--- image sizes ---
+ docker images --format '{{.Repository}}:{{.Tag}}\t{{.ID}}\t{{.Size}}'
+ grep ^foo
foo:squashed    e7ef74c229d7    120MB
foo:latest      b225b0dc0a0e    120MB