[Technology] docker.io/library/node container image size

As seen in my last post, the node image on docker is over 1GB. I was curious what contributed to that, so I ran and attached myself to a shell in it.

$ podman run -dt node bash
$ podman attach -l
root@...:/#

A quick query of installed packages and their sizes gave me these top 30 packages:

dpkg-query -Wf '${Installed-Size}\t${Package}\n' | sort -nr | head -n 30

Size (kB)	Deb Package	% (of installed packages)
68,236	gcc-12	7.65
47,784	libicu-dev	5.36
44,477	git	4.99
36,170	libicu72	4.05
36,161	g++-12	4.05
33,848	cpp-12	3.79
28,862	libperl5.36	3.23
19,446	libstdc++-12-dev	2.18
18,062	coreutils	2.02
17,816	perl-modules-5.36	1.99
16,203	libx265-199	1.81
15,021	binutils-common	1.68
14,577	mercurial-common	1.63
14,284	libgcc-12-dev	1.60
12,986	libc6	1.45
12,303	libssl-dev	1.38
11,957	libc6-dev	1.34
11,428	binutils-x86-64-linux-gnu	1.28
10,909	librsvg2-2	1.22
10,076	sq	1.13
10,075	libglib2.0-dev	1.13
9,404	libglib2.0-data	1.05
8,323	libpython3.11-stdlib	0.93
8,130	libmagic-mgc	0.91
8,017	libasan8	0.89
7,815	libtsan2	0.87
7,638	perl-base	0.85
7,164	bash	0.80
6,761	python3.11-minimal	0.75
6,589	linux-libc-dev	0.73

Surprisingly, no packages for nodejs/npm are listed! I calculated the sum of the size of all installed packages, and got 891,320 kB, but overall disk usage in the image's final file system is 1,139,008 kB. That's a discrepancy of 247,688 kB! Poking around to find some evidence of it, I see that npm is installed at /usr/local/bin/npm. All of /usr/local takes up 167,728 kB in the final image. Let's poke around and see which layer added that.

$ podman image tree node
Image ID: 386e0be86bde
Tags:     [docker.io/library/node:latest]
Size:     1.122GB
Image Layers
├── ID: 7c85cfa30cb1 Size: 121.3MB
├── ID: a9af9831483f Size: 49.56MB
├── ID: 68731f6c1e1e Size: 181.4MB
├── ID: d396cdbdc3ad Size: 596.9MB
├── ID: 02f1f39c8ec9 Size: 22.53kB
├── ID: 4709b21dad1d Size: 164.8MB
├── ID: 24d9598c79a8 Size: 7.626MB
└── ID: 19ba6ee0c874 Size: 3.584kB Top Layer of: [docker.io/library/node:latest]

$ podman history node
ID            CREATED     CREATED BY                                                                   SIZE              COMMENT
386e0be86bde  4 days ago  /bin/sh -c #(nop)  CMD ["node"]                                              0B                
<missing>     4 days ago  /bin/sh -c #(nop)  ENTRYPOINT ["docker-ent...                                0B                
<missing>     4 days ago  /bin/sh -c #(nop) COPY file:4d192565a7220e...                                3.58kB            
<missing>     4 days ago  /bin/sh -c set -ex   && for key in     6A0...                                7.63MB            
<missing>     4 days ago  /bin/sh -c #(nop)  ENV YARN_VERSION=1.22.19                                  0B                
<missing>     4 days ago  /bin/sh -c ARCH= && dpkgArch="$(dpkg --pri...                                165MB             
<missing>     4 days ago  /bin/sh -c #(nop)  ENV NODE_VERSION=20.7.0                                   0B                
<missing>     4 days ago  /bin/sh -c groupadd --gid 1000 node   && u...                                22.5kB            
<missing>     5 days ago  /bin/sh -c set -ex;                            apt-get update;   apt-...     597MB       
<missing>     5 days ago  /bin/sh -c apt-get update && apt-get insta...                                181MB             
<missing>     5 days ago  /bin/sh -c set -eux;                           apt-get update;   apt...      49.6MB      
<missing>     5 days ago  /bin/sh -c #(nop)  CMD ["bash"]                                              0B                
<missing>     5 days ago  /bin/sh -c #(nop) ADD file:ce04d6a354feaef...                                0B    

Taking a peak in ~/.local/share/containers/storage/overlay and doing a find against each of the layer IDs, looking for the npm binary, I get this:

./4709b21dad1d5d5cb88803c9c598c81fd9a94de38398ad002ec569cff33445c7/diff/usr/local/bin/npm
./4709b21dad1d5d5cb88803c9c598c81fd9a94de38398ad002ec569cff33445c7/diff/usr/local/lib/node_modules/corepack/shims/nodewin/npm
./4709b21dad1d5d5cb88803c9c598c81fd9a94de38398ad002ec569cff33445c7/diff/usr/local/lib/node_modules/corepack/shims/npm
./4709b21dad1d5d5cb88803c9c598c81fd9a94de38398ad002ec569cff33445c7/diff/usr/local/lib/node_modules/npm
./4709b21dad1d5d5cb88803c9c598c81fd9a94de38398ad002ec569cff33445c7/diff/usr/local/lib/node_modules/npm/bin/npm

Peaking at its directory structure, I see that that layer is 167,712 kB and accounts for all of /usr/local, and its entirely node files. Some of the most notable disk usage is as follows:

Size (kB)	Path	Comment
93,524	usr/local/bin/node	The binary itself.
53,004	usr/local/include/node/openssl/	Most of this in its archs/ subdirectory, with 21 architectures' .h files.
19,208	usr/local/lib/node_modules/
17,456	usr/local/lib/node_modules/npm
14,308	usr/local/lib/node_modules/npm/node_modules	Contains 196 modules, the largest as node-gyp at 3716 kB.

So, there you have it. The node image is so large mostly because it contains a tonne of development .deb packages, and node-specific files take up ~164 MB, about 14% of the final image.