Layers

Layers is small utility for software developers that use aufs to merge several layers project into one.

Why?

Layers allow to apply DRY principle to your project by merging several folders into one. Every software project has some files that are copied from project to project without modification.

Examples:

• configuration files for your development stack
• .gitignore files
• directory structure
• ... more samples?

Usually this files are copied once, and it's big work to update them all after.

Aufs to help

Aufs is layered filesystem that allows to merge several directories into one, and keep them writable. Layers utility use aufs, to compose layers automatically.

Installation

You need linux (not tested on other OSes yet) with aufs-tools installed, python-pip is also needed. Usually you have all those if you ever use Docker, if not then google how to install this tools.

Install Layers:

sudo pip install layers

As mount command against curent directory is not possible (shows "directory busy" error), add alias for layers command to execute it from parent dir, and then get you back in project directory. Execute in shell:

echo "layers() { LPD=\$PWD; cd ..; layers-util \$LPD \$@; cd \$LPD; }" >> ~/.bashrc
source ~/.bashrc

This will update your .bashrc automatically.

Quick start

Let's prepare example directory structure:

mkdir project1
mkdir some-layer
mkdir another

project1 - is our project directory. Another too are layers. We will put some data into "some-layer" and another:

echo "*.pyc" > some-layer/.gitignore
echo "Empty yet" > some-layer/README.txt

echo "John Doe (c) 2076 year" > another/AUTHOR.txt

Now create layers.yml file in your project1 directory, like this:

layers:

  every-python-project-should-have-this:
    path: ../some-layer

  just-my-ego:
    path: ../another

Now, lets mount this:

cd project1
layers mount

Now, ls should show the following:

ls project1

AUTHOR.txt  layers.yml  README.txt

Working with layers

If you make any changes in project1 directory, all changes will be recorded only on this layer, so, if we change project1/README.txt, it will not affect "some-layer":

$ cat project1/README.txt

Empty yet

$ echo "This is project readme" > project1/README.txt

$ cat project1/README.txt

This is project readme

$ cat some-layer/README.txt

Empty yet

But if you modify layers, changes are reflected:

$ echo ".more-to-ignore" >> some-layer/.gitignore

$ cat project1/.gitignore

*.pyc
.more-to-ignore

Auto-create mount-points

layers.yml have one interesting option that allow to create mount point before it mounted. For example it can be checked out from git:

layers:

  mfcloud-python:
    path: ../python-django
    create: git clone git@bitbucket.org:ribozz/python-django.git

Syntax here is:

create: {any valid bash command}

This may allow you to bootstrap your projects very quickly:

$ git clone my-repo-url-here my-project
$ cd my-project
$ layers mount

And magically all your layers are checked out and mounted.

Mount to different directory

"to" allows to mount to sub-directories:

layers:

  cratis:
    path: ../cratis
    create: git clone git@bitbucket.org:itpeople/cratis.git
    to: lib/cratis

  cratis-features:
    path: ../cratis-features
    create: git clone git@bitbucket.org:itpeople/cratis-features.git
    to: lib/cratis-features

  mfcloud-python:
    path: ../python-django
    create: git clone git@bitbucket.org:ribozz/python-django.git

Command reference

layers mount

Syntax:

layers mount

Mounts all layers referred in layers.yml

layers umount

Syntax:

layers umount

Unmounts all layers from current directory

layers commands

Syntax:

layers {some commmand}

chdir into every directory specified in layers.yml, and execute command. Example:

$ layers ls -la

Layer /home/alex/dev/example/project1

total 24
drwxrwxr-x 8 alex alex 4096 sept  30 14:43 .
drwxrwxr-x 5 alex alex 4096 sept  30 13:59 ..
-rw-rw-r-- 1 alex alex   23 sept  30 14:04 AUTHOR.txt
-rw-rw-r-- 1 alex alex   22 sept  30 14:46 .gitignore
-rw-rw-r-- 1 alex alex  113 sept  30 14:05 layers.yml
-rw-rw-r-- 1 alex alex   23 sept  30 14:43 README.txt

Layer /home/alex/dev/example/some-layer

total 24
drwxrwxr-x 4 alex alex 4096 sept  30 14:06 .
drwxrwxr-x 5 alex alex 4096 sept  30 13:59 ..
-rw-rw-r-- 1 alex alex   22 sept  30 14:46 .gitignore
-rw-rw-r-- 1 alex alex   10 sept  30 14:42 README.txt
-r--r--r-- 1 root root    0 sept  30 14:06 .wh..wh.aufs
drwx------ 2 root root 4096 sept  30 14:06 .wh..wh.orph
drwx------ 2 root root 4096 sept  30 14:06 .wh..wh.plnk

Layer /home/alex/dev/example/another

total 20
drwxrwxr-x 4 alex alex 4096 sept  30 14:06 .
drwxrwxr-x 5 alex alex 4096 sept  30 13:59 ..
-rw-rw-r-- 1 alex alex   23 sept  30 14:04 AUTHOR.txt
-r--r--r-- 1 root root    0 sept  30 14:06 .wh..wh.aufs
drwx------ 2 root root 4096 sept  30 14:06 .wh..wh.orph
drwx------ 2 root root 4096 sept  30 14:06 .wh..wh.plnk

Another useful command is:

layers git status

Licence

Apache licecne. See LICENCE for details

Changelog

0.1.5

• Improved handling of sub-mounts (to: ). (Alex.R.)

0.1.4

• Fix installation pocess in setup.py. (Alex. R.)
• Improved sh script, made it more user-friendly. Added instructions to README how to pudate bashrc (Alex.R.)

0.1.3

Added "to" to layers.yml (Alex R.)