An Amazon EBS constraint

September 27 2010, 7:17 AM  by Tamas Herman

Amazon Web Services are awesome in general. They have comprehensive documentation for each of their products. Even though the docs are concise, it's quite a lot of reading. So it has happened I missed a fact recently.

Amazon has 4 REGIONs, 2 in the US, 1 in Europe and 1 in Asia. They are identified by the following strings

  • us-east-1
  • us-west-1
  • eu-west-1
  • ap-southeast-1

(See more explanatory names under EC2 pricing for example)

These Regions are connected via the Internet.

Regions have multiple (Availability) ZONEs:

  • eu-west-1a
  • eu-west-1b
  • us-east-1a
  • us-east-1b
  • us-east-1c
  • us-east-1d
  • us-west-1a
  • us-west-1b
  • ap-southeast-1a
  • ap-southeast-1b

These are connected via a dedicated Internal network.

Which means Amazon doesn't have control over the connection between the Regions. They also have to pay for data transfers between Regions, so they will charge you for that too.

Another consequence is a constraint on EBS usage. The documentation states that EBS volumes can be snapshotted to S3 even in an incremental way and you can restore them into different Availability ZONEs. They don't say anything about how different these AZs can be. Apparently you can only do this within the same REGION where the snapshot was created. It's not bad, but it was a bit unexpected for me...

A quick reference how to obtain Region and Zone names:

$ ec2dre   # is short for ec2-describe-regions

REGION  eu-west-1       ec2.eu-west-1.amazonaws.com
REGION  us-east-1       ec2.us-east-1.amazonaws.com
REGION  us-west-1       ec2.us-west-1.amazonaws.com
REGION  ap-southeast-1  ec2.ap-southeast-1.amazonaws.com

$ for region in `ec2dre | cut -f2`; do ec2daz --region $region; done
# ec2daz is short for ec2-describe-availability-zones

AVAILABILITYZONE        eu-west-1a      available       eu-west-1
AVAILABILITYZONE        eu-west-1b      available       eu-west-1

AVAILABILITYZONE        us-east-1a      available       us-east-1
AVAILABILITYZONE        us-east-1b      available       us-east-1
AVAILABILITYZONE        us-east-1c      available       us-east-1
AVAILABILITYZONE        us-east-1d      available       us-east-1

AVAILABILITYZONE        us-west-1a      available       us-west-1
AVAILABILITYZONE        us-west-1b      available       us-west-1

AVAILABILITYZONE        ap-southeast-1a available       ap-southeast-1  
AVAILABILITYZONE        ap-southeast-1b available       ap-southeast-1

 

2841 views and 1 response

  • Sep 27 2010, 8:07 AM
    Tamas Herman responded:
    Btw, does anyone know how to query how much space are the snapshots taking from S3?