Wednesday, November 16, 2011

Tool of the Day: s3-bash - lightweight Amazon S3 access

When a server I have full control needs access to Amazon's S3 service, I usually turn to either duplicity or S3cmd. Both are polished tools that make it dang near trivial to push content to S3.

Today, however, I ran into a little bit a snag - I need to push thousands of files to S3, but I don't have full control over the server. Installing various libraries and such wasn't a possibility. My first assumption was that I was going to need to push the data to a server that did have s3cmd installed (probably using ssh+tar). Turns out, there was a better and simpler way: use s3-bash.

s3-bash, as the name implies, is a variety of s3 related scripts that leverage commonly installed tools. To my amazement (and appreciation!), I was able to upload these scripts to the serer in question, ssh in, and use them to access S3.

I took a peek in the files, and they really are masterfully written. Integrating with Amazon has some tricky requirements (such as the need to derive a request signature), and finding work arounds to do all this using standard tools is quite slick.

With that said, I couldn't help make my life a little easier by writing a wrapper shell script around the s3-* family of commands. The idea is that rather than specify the credentials on every command line use, my wrapper script could take care of that. Here's my wrapper:

#!/bin/bash

##
## A custom wrapper around s3-bash to make calling it easier
##

bash_home=/path/to/the/s3-bash/commands
secret=$bash_home/amz.secret
key=`cat $bash_home/amz.key`
headers=$bash_home/amz.headers
what=$1 ; shift

$bash_home/s3-$what -k $key -s $secret  -a $headers "$@"

I invoke this script by saying:

  s3 get -T foo /bucket.name/file/path/bar.txt

Notice how the script provides the -k and -s option, which are used for authentication. It also provides a -a argument, which provides Amazon specif headers. In my case, this file contains:

  x-amz-acl: public-read

This forces all files that I upload to be readable by the public.

With my s3 command in place, I was able to push a whole tree of files by running the command:

 find * -name '*.xlv' | while read f ; do echo $f ; s3 put -T $f /bucket.client.com/$f ; done

Gosh I love Linux! Add s3-bash to your toolkit today, you'll be glad you did.

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