Docker creates many layers while building the image. Sometimes it's not necessary or desireable to have them in the image. For example a Dockerfile ADD instruction creates a single layer with files you want to make available in the image. The problem arises when these files are only temporary files (for example product distribution that you want to unpack). Docker will carry this unnecessary layer always with the image, even if you delete these files in next layer. This a waste of time (more data to push/load/save) and resources (bigger image).
Squashing helps with organizing images in logical layers. Instead of having an image with multiple (in almost all cases) unnecessary layers - we can control the structure of the image.
- Can squash last n layers from an image
- Can squash from a selected layer to the end (not always possible, depends on the image)
- Support for Docker 1.9 or newer (older releases may run perfectly fine too, try it!)
- Squashed image can be loaded back to the Docker daemon or stored as tar archive somewhere
From source code
$ pip install --user https://github.com/goldmann/docker-squash/archive/master.zip
From PyPi
$ pip install docker-squash
$ docker-squash -h
usage: cli.py [-h] [-v] [--version] [-d] [-f FROM_LAYER] [-t TAG]
[--tmp-dir TMP_DIR] [--output-path OUTPUT_PATH]
image
Docker layer squashing tool
positional arguments:
image Image to be squashed
optional arguments:
-h, --help show this help message and exit
-v, --verbose Verbose output
--version Show version and exit
-d, --development Does not clean up after failure for easier debugging
-f FROM_LAYER, --from-layer FROM_LAYER
ID of the layer or image ID or image name. If not
specified will squash all layers in the image
-t TAG, --tag TAG Specify the tag to be used for the new image. By
default it'll be set to 'image' argument
--tmp-dir TMP_DIR Temporary directory to be used
--output-path OUTPUT_PATH
Path where the image should be stored after squashing.
If not provided, image will be loaded into Docker
daemon
MIT
We start with image like this:
$ docker history jboss/wildfly:latest IMAGE CREATED CREATED BY SIZE COMMENT 25954e6d2300 3 weeks ago /bin/sh -c #(nop) CMD ["/opt/jboss/wildfly/bi 0 B 5ae69cb454a5 3 weeks ago /bin/sh -c #(nop) EXPOSE 8080/tcp 0 B dc24712f35c4 3 weeks ago /bin/sh -c #(nop) ENV LAUNCH_JBOSS_IN_BACKGRO 0 B d929129d4c8e 3 weeks ago /bin/sh -c cd $HOME && curl -O https://do 160.8 MB b8fa3caf7d6d 3 weeks ago /bin/sh -c #(nop) ENV JBOSS_HOME=/opt/jboss/w 0 B 38b8f85e74bf 3 weeks ago /bin/sh -c #(nop) ENV WILDFLY_SHA1=c0dd7552c5 0 B ae79b646b9a9 3 weeks ago /bin/sh -c #(nop) ENV WILDFLY_VERSION=10.0.0. 0 B 2b4606dc9dc7 3 weeks ago /bin/sh -c #(nop) ENV JAVA_HOME=/usr/lib/jvm/ 0 B 118fa9e33576 3 weeks ago /bin/sh -c #(nop) USER [jboss] 0 B 5f7e8f36c3bb 3 weeks ago /bin/sh -c yum -y install java-1.8.0-openjdk- 197.4 MB 3d4d0228f161 3 weeks ago /bin/sh -c #(nop) USER [root] 0 B f7ab4ea19708 3 weeks ago /bin/sh -c #(nop) MAINTAINER Marek Goldmann < 0 B 4bb15f3b6977 3 weeks ago /bin/sh -c #(nop) USER [jboss] 0 B 5dc1e49f4361 3 weeks ago /bin/sh -c #(nop) WORKDIR /opt/jboss 0 B 7f0f9eb31174 3 weeks ago /bin/sh -c groupadd -r jboss -g 1000 && usera 4.349 kB bd515f044af7 3 weeks ago /bin/sh -c yum update -y && yum -y install xm 25.18 MB b78336099045 3 weeks ago /bin/sh -c #(nop) MAINTAINER Marek Goldmann < 0 B 4816a298548c 3 weeks ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0 B 6ee235cf4473 3 weeks ago /bin/sh -c #(nop) LABEL name=CentOS Base Imag 0 B 474c2ee77fa3 3 weeks ago /bin/sh -c #(nop) ADD file:72852fc7626d233343 196.6 MB 1544084fad81 6 months ago /bin/sh -c #(nop) MAINTAINER The CentOS Proje 0 B
And we want to squash all the layers down to layer 4bb15f3b6977.
$ docker-squash -f 4bb15f3b6977 -t jboss/wildfly:squashed jboss/wildfly:latest 2016-04-01 13:11:02,358 root INFO docker-scripts version 1.0.0dev, Docker 7206621, API 1.21... 2016-04-01 13:11:02,358 root INFO Using v1 image format 2016-04-01 13:11:02,374 root INFO Old image has 21 layers 2016-04-01 13:11:02,378 root INFO Checking if squashing is necessary... 2016-04-01 13:11:02,378 root INFO Attempting to squash last 12 layers... 2016-04-01 13:11:02,378 root INFO Saving image 25954e6d230006235eecb7f0cc560264d73146985c2d2e663bac953d660b8730 to /tmp/docker-squash-fbxZz4/old/image.tar file... 2016-04-01 13:11:08,003 root INFO Image saved! 2016-04-01 13:11:08,031 root INFO Unpacking /tmp/docker-squash-fbxZz4/old/image.tar tar file to /tmp/docker-squash-fbxZz4/old directory 2016-04-01 13:11:08,588 root INFO Archive unpacked! 2016-04-01 13:11:08,636 root INFO Squashing image 'jboss/wildfly:latest'... 2016-04-01 13:11:08,637 root INFO Starting squashing... 2016-04-01 13:11:08,637 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/25954e6d230006235eecb7f0cc560264d73146985c2d2e663bac953d660b8730/layer.tar'... 2016-04-01 13:11:08,637 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/5ae69cb454a5a542f63e148ce40fb9e01de5bb01805b4ded238841bc2ce8e895/layer.tar'... 2016-04-01 13:11:08,637 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/dc24712f35c40e958be8aca2731e7bf8353b9b18baa6a94ad84c6952cbc77004/layer.tar'... 2016-04-01 13:11:08,638 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/d929129d4c8e61ea3661eb42c30d01f4c152418689178afc7dc8185a37814528/layer.tar'... 2016-04-01 13:11:09,113 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/b8fa3caf7d6dc228bf2499a3af86e5073ad0c17304c3900fa341e9d2fe4e5655/layer.tar'... 2016-04-01 13:11:09,115 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/38b8f85e74bfa773a0ad69da2205dc0148945e6f5a7ceb04fa4e8619e1de425b/layer.tar'... 2016-04-01 13:11:09,115 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/ae79b646b9a9a287c5f6a01871cc9d9ee596dafee2db942714ca3dea0c06eef3/layer.tar'... 2016-04-01 13:11:09,115 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/2b4606dc9dc773aa220a65351fe8d54f03534c58fea230960e95915222366074/layer.tar'... 2016-04-01 13:11:09,115 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/118fa9e33576ecc625ebbbfdf2809c1527e716cb4fd5cb40548eb6d3503a75a9/layer.tar'... 2016-04-01 13:11:09,115 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/5f7e8f36c3bb20c9db7470a22f828710b4d28aede64966c425add48a1b14fe23/layer.tar'... 2016-04-01 13:11:10,127 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/3d4d0228f161b67eb46fdb425ad148c31d9944dcb822f67eac3e2ac2effefc73/layer.tar'... 2016-04-01 13:11:10,129 root INFO Squashing file '/tmp/docker-squash-fbxZz4/old/f7ab4ea197084ab7483a2ca5409bdcf5473141bfb61b8687b1329943359cc3fe/layer.tar'... 2016-04-01 13:11:10,732 root INFO Squashing finished! 2016-04-01 13:11:10,737 root INFO New squashed image ID is 52255e75d3eb83123e074f897e8c971dec9d1168a5c82d7c1496a190da2e40ef 2016-04-01 13:11:14,563 root INFO Image registered in Docker daemon as jboss/wildfly:squashed 2016-04-01 13:11:14,652 root INFO Done
We can now confirm the layer structure:
$ docker history jboss/wildfly:squashed IMAGE CREATED CREATED BY SIZE COMMENT 52255e75d3eb 40 seconds ago 358.2 MB 4bb15f3b6977 3 weeks ago /bin/sh -c #(nop) USER [jboss] 0 B 5dc1e49f4361 3 weeks ago /bin/sh -c #(nop) WORKDIR /opt/jboss 0 B 7f0f9eb31174 3 weeks ago /bin/sh -c groupadd -r jboss -g 1000 && usera 4.349 kB bd515f044af7 3 weeks ago /bin/sh -c yum update -y && yum -y install xm 25.18 MB b78336099045 3 weeks ago /bin/sh -c #(nop) MAINTAINER Marek Goldmann < 0 B 4816a298548c 3 weeks ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0 B 6ee235cf4473 3 weeks ago /bin/sh -c #(nop) LABEL name=CentOS Base Imag 0 B 474c2ee77fa3 3 weeks ago /bin/sh -c #(nop) ADD file:72852fc7626d233343 196.6 MB 1544084fad81 6 months ago /bin/sh -c #(nop) MAINTAINER The CentOS Proje 0 B
Other option is to specify how many layers (counting from the newest layer) we want to squash.Let's squash last 10 layers from the jboss/wildfly:latest image:
$ docker-squash -f 10 -t jboss/wildfly:squashed jboss/wildfly:latest 2016-04-01 13:15:06,488 root INFO docker-scripts version 1.0.0dev, Docker 7206621, API 1.21... 2016-04-01 13:15:06,488 root INFO Using v1 image format 2016-04-01 13:15:06,504 root INFO Old image has 21 layers 2016-04-01 13:15:06,504 root INFO Checking if squashing is necessary... 2016-04-01 13:15:06,504 root INFO Attempting to squash last 10 layers... 2016-04-01 13:15:06,505 root INFO Saving image 25954e6d230006235eecb7f0cc560264d73146985c2d2e663bac953d660b8730 to /tmp/docker-squash-fu80CX/old/image.tar file... 2016-04-01 13:15:12,136 root INFO Image saved! 2016-04-01 13:15:12,167 root INFO Unpacking /tmp/docker-squash-fu80CX/old/image.tar tar file to /tmp/docker-squash-fu80CX/old directory 2016-04-01 13:15:12,706 root INFO Archive unpacked! 2016-04-01 13:15:12,756 root INFO Squashing image 'jboss/wildfly:latest'... 2016-04-01 13:15:12,756 root INFO Starting squashing... 2016-04-01 13:15:12,756 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/25954e6d230006235eecb7f0cc560264d73146985c2d2e663bac953d660b8730/layer.tar'... 2016-04-01 13:15:12,757 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/5ae69cb454a5a542f63e148ce40fb9e01de5bb01805b4ded238841bc2ce8e895/layer.tar'... 2016-04-01 13:15:12,757 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/dc24712f35c40e958be8aca2731e7bf8353b9b18baa6a94ad84c6952cbc77004/layer.tar'... 2016-04-01 13:15:12,757 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/d929129d4c8e61ea3661eb42c30d01f4c152418689178afc7dc8185a37814528/layer.tar'... 2016-04-01 13:15:13,234 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/b8fa3caf7d6dc228bf2499a3af86e5073ad0c17304c3900fa341e9d2fe4e5655/layer.tar'... 2016-04-01 13:15:13,235 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/38b8f85e74bfa773a0ad69da2205dc0148945e6f5a7ceb04fa4e8619e1de425b/layer.tar'... 2016-04-01 13:15:13,235 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/ae79b646b9a9a287c5f6a01871cc9d9ee596dafee2db942714ca3dea0c06eef3/layer.tar'... 2016-04-01 13:15:13,235 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/2b4606dc9dc773aa220a65351fe8d54f03534c58fea230960e95915222366074/layer.tar'... 2016-04-01 13:15:13,236 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/118fa9e33576ecc625ebbbfdf2809c1527e716cb4fd5cb40548eb6d3503a75a9/layer.tar'... 2016-04-01 13:15:13,236 root INFO Squashing file '/tmp/docker-squash-fu80CX/old/5f7e8f36c3bb20c9db7470a22f828710b4d28aede64966c425add48a1b14fe23/layer.tar'... 2016-04-01 13:15:14,848 root INFO Squashing finished! 2016-04-01 13:15:14,853 root INFO New squashed image ID is fde7edd2e5683c97bedf9c0bf52ad5150db5650e421de3d9293ce5223b256455 2016-04-01 13:15:18,963 root INFO Image registered in Docker daemon as jboss/wildfly:squashed 2016-04-01 13:15:19,059 root INFO Done
Let's confirm the image structure now:
$ docker history jboss/wildfly:squashed IMAGE CREATED CREATED BY SIZE COMMENT fde7edd2e568 32 seconds ago 358.2 MB 3d4d0228f161 3 weeks ago /bin/sh -c #(nop) USER [root] 0 B f7ab4ea19708 3 weeks ago /bin/sh -c #(nop) MAINTAINER Marek Goldmann < 0 B 4bb15f3b6977 3 weeks ago /bin/sh -c #(nop) USER [jboss] 0 B 5dc1e49f4361 3 weeks ago /bin/sh -c #(nop) WORKDIR /opt/jboss 0 B 7f0f9eb31174 3 weeks ago /bin/sh -c groupadd -r jboss -g 1000 && usera 4.349 kB bd515f044af7 3 weeks ago /bin/sh -c yum update -y && yum -y install xm 25.18 MB b78336099045 3 weeks ago /bin/sh -c #(nop) MAINTAINER Marek Goldmann < 0 B 4816a298548c 3 weeks ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0 B 6ee235cf4473 3 weeks ago /bin/sh -c #(nop) LABEL name=CentOS Base Imag 0 B 474c2ee77fa3 3 weeks ago /bin/sh -c #(nop) ADD file:72852fc7626d233343 196.6 MB 1544084fad81 6 months ago /bin/sh -c #(nop) MAINTAINER The CentOS Proje 0 B