In the usual spirit of social coding, I have added the script to Github: https://github.com/elubow/ec2-consistent-snapshot.

Running it is just this:

The options used here (for reference) are telling ec2-consistent-snapshot to use –mongo, on the –xfs-filesystem /data, in the us-east-1 –region (note that it’s just the region and not the availability zone within that region), to be backed up with the listed –description of the specified volumes. You can even throw a –mongo-stop in there to have Mongo stopped before the file system freeze and then restarted after the volumes have been backed up. Don’t forget that you need to set your Amazon keys in you environment variables (AMAZON_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY for your key and secret respectively).

I attempted to keep the usage style consistent with Eric Hammond’s original version, just add Mongo support for it.

Note: I also mentioned this on the mailing list. But given the amount of messages that fly around on the list daily, some folks may have missed it.

References:

• ec2-consistent-snapshot blog entry by Eric Hammond
• ec2-consistent-snapshot on Github with Mongo DB support
• Backing up MongoDB on EC2 (10gen)

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I stumbled across a post that talks about mimicking Perl’s autovivification here. But I wanted a data structure (specifically a hash) that would be created on demand. So here is a class that creates a recursive hash.

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This will ensure that you have a unique UUID when INSERTing the job. But I think that we can do better and this is where the good practice comes into effect (and why the Gearman devs marked it as won’t fix). So let’s think a little more abstractly for a moment. For the uniq key (unique_key column), how about something like “${type}_”.create_uuid_as_string(). This will allow us to group (in this case) our mailing types so that we can monitor the status of our work queue. Yes, we can easily hop into the database and run this query:

But wouldn’t it be nicer to know exactly where we are at with this query:

For reference, here are the unique_key columns that allowed to generate that query:

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By reading the Pod documentation, you’ll also find that you can get a lot more specific. You can add command line switches, lots of performance data, and my favorite, some pretty extensive success, warning or critical messages that can be displayed on the dashboard.

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I noticed that when I tried to read the file (if it already existed), then nothing would be read. I neglected to realize that you must seek to position 0 in the file if you want to read it. Therefore the following code will work:

Although it might seem obvious that you need to be at the beginning of the file to read it forward (and it is), I didn’t realize the file pointer opened a file in append mode to the last position in the file (in hind sight, it does appear to be a bit more obvious).

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This will print:

This neat little method takes advantage of Perl C API’s looks_like_number() function. Since this is virtually native, it will be pretty fast.

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One of the ways to deal with it to to use grep. Since grep returns the number of elements in the array that evaluate to true (when called in a scalar context), I can do the following to make it work:

The reason this works is that when called in the scalar context, grep only returns the number of elements that evaluate to true. Since there are 3 elements in the array, the return value is greater than 2, then the entire expression evaluates to true. This is not only a lot easier to read and a lot cleaner to write, but it makes for easy additions to the conditional testing if necessary. Although changing the context in which functions are called is common, it is easily forgotten. Grep called in scalar context can be easily manipulated (as above) to add readability to your program.

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I had a little trouble finding out how to fix this. So I am posting this here in case it helps someone else out. It was a simple fix (since CPAN doesn’t work) that you have to do by hand. Go to the CPAN site and download dist IO here. Download and untar it and run the following commands:

This should fix your Perl install. It also ended up that I had to run CPAN and reinstall Scalar::Util and Storable.

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use strict;
use warnings;
use Proc::ProcessTable;

 # Create a new process table object
 my ($pt) = new Proc::ProcessTable;

 # Initialize your process table hash
 my (%pt_hash);

 # Get the fields that your architecture supports
 my (@fields) = $pt->fields;

 # Outer loop for each process id
 foreach my $proc ( @{$pt->table} ) {
    # Inner loop for each field within the process id
    for my $field (@fields) {
       # Add the field to the hash
       $pt_hash{$proc->pid}{$field} = $proc->$field();
    }
 }

It’s just as simple as that. If you want to be sure that its in there. At the end of the file add these two lines for proof:

use Data::Dumper;
print Dumper \%pt_hash;

The hash is organized with the keys being the process ids. There is another hash underneath it with all the fields as hash keys.

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