Wednesday, February 7, 2024

IPv6 Only Ubuntu instance on Amazon Web Services

Pay Per IPv4 Address?

You're probably aware of the AWS plan charge for IPv4 Addresses.  The costs for an address is$0.005 per hour, which amounts to about $3.65/month.  That's not going to break the bank, but if you use a few tiny instances (t3.micro or even t3.nano) you might pay more for the IP address than for the virtual machine it's attached to.  

Secondarily, I wondered if I can create an EC2 instance that has only IPv6, and would there be problems?  I decided to try.

Configuring IPv6 on EC2

Setting up IPv6 on EC2 takes a little work, most of it being done in the VPC.  Amazon has documentation that explains it.  The gist is:

  1. Associate a public IPv6 border address block to your VPC.  To do this, open the VPC console, select the VPC your instances are on, and edit the CIDR blocks.  Add an "Amazon-provided IPv6 CIDR block" associated with your ec2 region or AZ
  2. Create at least one subnet within that block. Typically this will be a subset of the block (for example a /64).  Your instances will choose an address from within this subnet.
  3. Make sure your EC2 instance belongs to this VPC/subnet (if it doesn't already) and auto-assign it an address
  4. Update the routing tables to include an IPv6 default rout

My instructions here are very incomplete, but the Amazon instructions are good (though long), so follow those.

APT Updates

The first pain point I ran into was breaking apt.  There are two reasons for this.  One is that you have to specifically configure apt to use IPv6.  You can do this by adding a file:

root# cat /etc/apt/apt.conf.d/1000-force-ipv6-transport
Acquire::ForceIPv6 "true";

Second, if you built your Ubuntu instance from one of the EC2 templates, it's going to have apt repositories listed that don't support IPv6.  In my case this was  It surprises me that there would be such a repository, obviously within AWS, but without an IPv6 address.

To fix this, I changed /etc/apt/sources.list to point toward a more generic Ubuntu package source:

deb jammy main restricted
deb jammy-updates main restricted
deb jammy universe
deb jammy-updates universe

This probably has some speed implications, and most likely some cost implications as well as the package repository is no longer within the AWS region as your instance, but that is likely to cost you pennies at most and the speed isn't that important for regular patching and updates.

Is it connectable?

All the testing I have done so far has been fine.  I work at a place that has good IPv6 infrastructure, as does my cable internet service (Spectrum).  Mobile devices seem to be ahead of the curve with respect to IPv6.  So, for my use case, IPv6 only seems fine.  I do have concerns, though, about connectivity - how many IPv4-only clients are out there?  No idea.  I don't think I would risk it for a truly "production" application until I understand the answer to that question.


Docker containers running within the EC2 instance are a little more problematic.  If those containers need to reach out to the internet for any reason, they won't work unless you specifically enable IPv6 (or set up some kind of proxy) for them.  That's an issue I was abled to solve, and I will explain how another day.