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An extensible framework to synchronize a local directory to a remote location. Will support S3, Rackspace and generic http based workflows

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Ever have a work-flow that requires a copy of a directory be maintained in another location?

Perhaps you created a cronjob task that looks like this?

* * * * * s3put -w -b my_bucket /home/my/stuff

The copying entire directories from point A to point B is a common system anti-pattern. Most tools that solve this are procedural: their semantics state that files are to be copied from target to source. Far better would be a declarative approach - define a target directory that should be left in sync with a source and simple run a tool to maintain this state.

At WNYC we wrote autosync to solve this very problem. Autosync is an easy to extend framework that takes care of mirroring and keeping mirrored files from one location to another. Out of the box it supports Amazon S3; Rackspace support is provided in the backend creation example.

Superficially it isn't all that dissimilar from while true; do s3put ... ; sleep 1; done. Except it is faster and uses fewer resources than conventional solutions to this problem.


Autosync is a registered package in the pypi repository; it can be installed with pip:

pip install autosync


Running autosync requires only a source directory path and information about the desired target. By default autosync writes to S3; the configuration for an S3 uploader can be as simple as:

autosync --target_container=my_s3_bucket --source_prefix=/var/data /var/data/files

In this example files are copied from /var/data/files, /var/data is stripped from each file's absolute path and this file is written to my_s3_bucket.

Other targets can be specified with the actor parameter.

--actor: The full name of the module and class use to generate a connection to the target. So if you created a connection object called my.foobar.Connection you would type --actor=my.foobar.Connection. Modules included with autosync (i.e. autosync.actors.*.Connection) can be abbreviated with the base module name (i.e. --actor=s3) (default: 's3')

Source filter restricts which of the files in the source directory are copied.

--source_filter: Only accept files that match this regex (default: '^.*$')

Most backend systems have some notion of drives, containers, buckets, repos - whatever its called, it goes into this parameter.

--target_container: The remote bucket to write into. This would be an S3 bucket, rackspace container, rsync host and module or maybe Drive letter in Windows


Autosync has no configuration files. It does use boto which will need to be provided login credentials.


One of the most important concepts to keep track of when configuring autosync is the "source_prefix". Folks who use s3put a lot will already know about the -P flag, but I'll review it anyway.

Imagine you have a directory structure hanging off of your root directory that looks like this:


If you type this:

# cd 
# tar -cvzf mystuff.tar.gz mystuff

you will create a tar file laid out like this:


But if you type this instead:

# cd ~/mystuff
# tar -cvzf mystuff.tar.gz * 

you will create a tar file with a layout that looks like this:


With tar and zip the current directory defines the root of your tree.

In autosync this root is made explicit. When running autosync if you say:

autosync mystuff

the resulting tree structure will look this:


Probably not what you want.

To stop this you add what is called a "source prefix". So if you say:

$ autosync --source_prefix="/home/" mystuff

the resulting file system will look like this:


You can get the same automatic behavior of more traditional tools; if you are working from bash you might say:

autosync --source_prefix=$PWD/mystuff/ mystuff

which will give you a file layout that looks like this:


Note the trailing slash. If you omit the trailing slash and write:

autosync --source_prefix=$PWD/mystuff/ mystuff

which will give you a file layout that looks like this


Depending on your backend this could mean something very different. It doesn't for Amazon S3, but at least one of WNYC's internal work flows uses os.path.join to connect the bucket and file name. os.path.join is sensitive to leading slashes in file names:

>>> import SOs.path
>>> os.path.join('a', 'b') 
>>> os.path.join('a', '/b') 

Don't accidentally convert something to an absolute path if you don't mean to.

While you might not want your files to be in the /home/adeprince directory on S3, you might also not want them to be in the root directory. No problem, autosync also supports target prefixes. These are added to the front of your path, so if you said:

autosync --source_prefix=$PWD/mystuff/ --target-prefix=/foo/bar/ mystuff

your file structure would look like this


Extending autosync

Now lets look at how autosync is extended. There there three steps to extending autosync:

You want auto sync's main method to know about any parameters that might be specific to your application. Fortunately gflags make this really painlessly easy.

Recall in the above example we need to add two additional parameters beyond the defaults in autosync: url and secret. To do this we write:

import gflags
FLAGS = gflags.FLAGS
gflags.DEFINE_string('url', None, 'Base url to connect to (i.e.')
gflags.DEFINE_string('secret', None, 'Secret API key')

Now the next step is to create a a class that implements the autosync actor interface. This interface requires three methods:

list returns a generator that produces autosync.files.File compatible objects describing what's already in your data store. Recall autosync is threaded -- if this data is sorted by primary key autosync is able to perform a merge and determine which files need to be added or removed before the download of file listings is complete. To indicate this the returned generate should have an attribute called already_sorted and it should be true.

delete accepts a single parameter, key, that is also a File compatible object. The primary key of the object to delete is in key.key

upload accepts a single parameter, key, that is also a File compatible object. This is used to indicate that the file should be created or updated.

From this email I omit the complete implementation of's MediaFileActor class, but you are welcome to look in puppy/scripts.

Lastly you need to "register" your actor with autosync and run autosync. You do this with the following code snippet:

if __name__ == "__main__":

The full source to the rackspace example can be found in

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