Docker images require appropriate shared object files (".so") to run. Rather than assume Ubuntu has the correct lib's, use ldd to get a list and install the ones you know you need. This can reduce the underlying images from GB to a few MB.

1. Reduce, Reuse, Recycle:
Repeatable library images for Docker.
Steven Lembark
Workhorse Computing
lembark@wrkhors.com

2. Distributing Docker Images
Stock doc's use Ubuntu distro image.
Includes systemd, among other things.
Bloated

3. Distributing Docker Images
Why distro?
/bin?
/usr/bin?
/sbin?
/var/spool?

4. Distributing Docker Images
Why distro?
Shared Object Lib's (.so).

5. Distributing Docker Images
Why distro?
Shared Object Lib's (.so).
Your executable + Ubuntu == runnable.

6. Distributing Docker Images
Why distro?
Shared Object Lib's (.so).
Your executable + Ubuntu != runnable.
Except when it isn't.

7. Docker is not a VM
Execuatables use versions of lib's.
Not all versions are [bug-] compatible.
RH/SuSE/Arch/Gentoo + Ubuntu == ???
libc differences are the worst.
What you need are your libs.

8. Q: How to distribute?
One approach: Dup /lib*, /usr/lib* .
4 /lib32
38 /lib64
372 /usr/lib32
2526 /usr/lib64
About 3GB on my notebook.
Development server? (ouch)

9. What you need is all you want
Q: What do you need?

10. What you need is all you want
Q: What do you need?
A: Ask.
ldd lists SO paths.

11. What you need: ask ldd
# Path to .so and virtual offset of entry point.
$ ldd /opt/bin/perl
linux-vdso.so.1 (0x00007ffee215e000)
libperl.so => /opt/perl/5.22/lib/5.22.0/x86_64-
linux/CORE/libperl.so (0x00007f6b40026000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f6b3fe0a000)
libnsl.so.1 => /lib64/libnsl.so.1 (0x00007f6b3fbf2000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f6b3f9ee000)
libm.so.6 => /lib64/libm.so.6 (0x00007f6b3f6f2000)
libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007f6b3f4bb000)
libutil.so.1 => /lib64/libutil.so.1 (0x00007f6b3f2b8000)
libc.so.6 => /lib64/libc.so.6 (0x00007f6b3ef1d000)
/lib64/ld-linux-x86-64.so.2 (0x00007f6b40417000)

12. What don't you need?
Then again, not everything needs shared lib's:
$ ldd /opt/perl/lib/5.22.0/NEXT.pm
ldd: warning: you do not have execution permission for
`/opt/perl/lib/5.22.0/NEXT.pm'
not a dynamic executable

13. Q: How do you ask for what you need?
More than one way...

14. 1. Scan it all.
Scan all of perl5's lib.
ldd everything.
filter out rejects.
uniq the rest.
Good: One image for everything.
Bad: Big (?)

15. 2. Scan current
Construct docker's source directory.
Scan that with ldd.
App From "-libs" image.
Good: Small.
Bad: More work.

16. 2. Scan current
Construct docker's source directory.
Scan that with ldd.
App From "-libs" image.
Good: Small.
Bad: More work.
Good: Easy to automate.

17. Q: Which PM's do I need?
A: Ask perl.
%INC has all of your module paths.
x %INC
0 HASH(0x24d8070)
'/opt/perl/5.22/lib/site_perl/5.22.0/x86_64-
linux/auto/Term/ReadLine/Gnu/XS/autosplit.ix' =>
'/opt/perl/5.22/lib/site_perl/5.22.0/x86_64-
linux/auto/Term/ReadLine/Gnu/XS/autosplit.ix'
'AutoLoader.pm' => '/opt/perl/5.22/lib/5.22.0/AutoLoader.pm'
'B.pm' => '/opt/perl/5.22/lib/5.22.0/x86_64-linux/B.pm'

18. Q: Which PM's do I need?
A: Ask perl.
%INC has all of your module paths.
Hard to export for arbitrary program.
x %INC
0 HASH(0x24d8070)
'/opt/perl/5.22/lib/site_perl/5.22.0/x86_64-
linux/auto/Term/ReadLine/Gnu/XS/autosplit.ix' =>
'/opt/perl/5.22/lib/site_perl/5.22.0/x86_64-
linux/auto/Term/ReadLine/Gnu/XS/autosplit.ix'
'AutoLoader.pm' => '/opt/perl/5.22/lib/5.22.0/AutoLoader.pm'
'B.pm' => '/opt/perl/5.22/lib/5.22.0/x86_64-linux/B.pm'

19. So: Bulk is it.
cd /opt/perl;
find -H lib bin -type f |
xargs ldd 2>/dev null |
grep '.so' | grep -v ':$';

20. Menagrie of sharing
linux-vdso.so.1 (0x00007ffe8d3f6000)
libc.so.6 => /lib64/libc.so.6 (0x00007ff244e37000)
/lib64/ld-linux-x86-64.so.2 (0x00005622e44ad000)
linux-vdso.so.1 (0x00007fffe4075000)
libc.so.6 => /lib64/libc.so.6 (0x00007f92f978f000)
/lib64/ld-linux-x86-64.so.2 (0x00005622e63a1000)

21. Menagrie of sharing
linux-vdso.so.1 (0x00007ffe8d3f6000)
Q: Why no path?
A: This is a kernel binding.
No file on disk.

22. Menagrie of sharing
linux-vdso.so.1 (0x00007ffe8d3f6000)
Q: Why no path?
A: This is a kernel binding.
No file on disk.
Be careful what you search for!

23. ldd uses fat commas
find -H /opt/perl/lib |
xargs ldd 2>/dev/null |
grep '=>' | cut -d ' ' -f3|
sort -d | uniq ;

24. ldd uses fat commas
Except when it doesn't:
/lib64/libresolv.so.2
/lib64/librt.so.1
/lib64/libtinfo.so.6
/lib64/libutil.so.1
/lib64/libz.so.1
not
/usr/lib32/libatk-1.0.so.0
/usr/lib32/libbz2.so.1
/usr/lib32/libcairo.so.2

25. cpio copies paths
Copy to build dir.
cpio ignores "not", keeps going.
#!/bin/bash
cd $(dirname $0);
dirs='/opt/perl/{lib,bin}';
find $dirs | xargs ldd | cut | sort | uniq |
cpio -pdv . ;

26. Result:
$ ls -a -1
.dockerignore
build
Dockerfile
lib32
lib64
usr
$ du -msx; # compare to 3000MB!
8

27. Dockerfile
FROM empty
MAINTAINER lembark@wrkhors.com
Alternative:
FROM busybox

28. .dockerignore
One line: build

29. Command line
$ docker build --rm .
http://host:5000/lembark/perl-so;
Not so bad.

30. build script
#!/bin/bash
cd $(dirname $0);
name=$(basename $(dirname $PWD));
find -H /opt/perl/{bin,lib} -type f |
xargs ldd 2>/dev/null |
grep '=>' | cut -d' ' -f3 |
uniq | sort -d | uniq |
cpio -pd . ;
docker build --rm .
http://localhost:5000/$(whoami)/$name;

31. perl-exec from perl-so
FROM .../lembark/perl-so
All the libs you need.
In one place.

32. Summary
Code requires SO's.
If SO's match things work.
Get what you need using ldd.
Dockerize perl from SO image.
Result: Truly Lazy Docker.