This directory demostrates several Docker topics:

• Minimal Docker images (all less than 3 MB).

• Rootfs concept inside the Docker images/containers.

• Dependencies on runtime components (e.g., .so files).

• Isolation of resources.

The program walk-tree tries to traverse directory structures starting from specified path (or . by default). For brevity, it excludes /dev, /proc, and /sys directories from the output.

Two versions of the same functionality are provided:

1. Go version walk-tree-go: a fully statically-linked ELF executable (i.e., without runtime dependencies on any .so files).

2. C version walk-tree-c: an ordinary ELF executabie with runtime dependencies on some system-wide .so files:

   $ ldd walk-tree-c
           linux-vdso.so.1 =>  (0x00007fff899f4000)
           libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f0e2a191000)
           /lib64/ld-linux-x86-64.so.2 (0x00007f0e2a55f000)

Refer to the src directory if you're courious about their source code.

The program walk-tree-go is a fully statically-linked ELF executable.

★★ To build it into a minimal Docker image with Dockerfile:

$ docker build .

To see what's inside this image, starting from its root directory /:

$ docker run  IMAGE-ID  walk-tree-go  /

The program walk-tree-c is a dynamically-linked ELF executable with runtime dependencies on some system-wide .so files.

★★ To build it into a minimal Docker image with Dockerfile:

$ docker build .

To see what's inside this image, starting from its root directory / (will fail!):

$ docker run  IMAGE-ID  walk-tree-c  /

Extract required .so files from CentOS 5.11:

 142488  Sep 16 2014  ld-linux-x86-64.so.2
1720712  Sep 16 2014  libc.so.6

Then, pack them, together with walk-tree-c, into the tarball rootfs-from-centos511.tar.gz.

★★ To build it into a minimal Docker image with Dockerfile:

$ docker build .

To see what's inside this image, starting from its root directory /:

$ docker run  IMAGE-ID  walk-tree-c  /

Extract required .so files from Ubuntu 14.04:

 149120  Feb 25 2015  ld-linux-x86-64.so.2
1840928  Feb 25 2015  libc.so.6

Then, pack them, together with walk-tree-c, into the tarball rootfs-from-ubuntu1404.tar.gz.

★★ To build it into a minimal Docker image with Dockerfile:

$ docker build .

To see what's inside this image, starting from its root directory /:

$ docker run  IMAGE-ID  walk-tree-c  /

System-wise .so files from CentOS 5.11:

 142488  Sep 16 2014  ld-linux-x86-64.so.2
1720712  Sep 16 2014  libc.so.6

System-wise .so files from Ubuntu 14.04:

 149120  Feb 25 2015  ld-linux-x86-64.so.2
1840928  Feb 25 2015  libc.so.6

Can these two suites co-exist at the same time? Dependency hell?