increase EC2 EBS volume after cloning - resize2fs

Question

This is a very similar problem to EC2 Can't resize volume after increasing size. However, I cannot resolve this manually using fdisk because I'm trying to get the whole process to run automatically.

I'm using a python boto (2.39) script (snippet) which takes a snapshot, registers a new AMI with the same block device mapping, and then creates an instance from it.

It's all working well. The new instance is created with a larger volume size. The new instance is loading ok. The only problem I see is that the partition size is kept at the original size instead of the full size.

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda1      7.8G  2.4G  5.0G  33% /

when I run resize2fs it doesn't do anything

$ resize2fs /dev/xvda1
resize2fs 1.42.12 (29-Aug-2014)
The filesystem is already 2096128 (4k) blocks long.  Nothing to do!

Is there a way to run something automatically (scripted) to fix this, or something to do when cloning the image? I'm not using Amazon Linux AMI but rather a debian-based AMI.

Answer 1

Amazon Linux will automatically resize the root filesystem to the full size of the volume. This was introduced in Amazon Linux AMI 2014.03.

From the release notes:

Cloud-Init 0.7.2

Cloud-Init has been updated to the 0.7 series, adding a number of useful features. One example is dracut-modules-growroot, which automatically resizes your root filesystem on boot.