I have been digging into network traffic to truly understand all the sources and destinations when using AWS services - specifically S3 and Yum.
This is important to understand if you have any legal requirements that dictate all your traffic must be maintained in a particular region. It is also important to understand what traffic is encrypted, unencrypted, inside and outside your VPC (Virtual Private Cloud). Additionally it is always a good idea to know the exact source of your software packages.
We would presume that yum updates should go over an encrypted, private network, but this does not always seem to be the case. This is why it's a good idea to monitor your network and ensure your software packages are coming from the source you expect. I would recommend an internal software repository carefully monitored to ensure the updates are always from the correct source.
In my case I was running a Yum update from the us-west-2 AWS region (Oregon, US) and I noticed traffic going to the southeast Asia-Pacific region. Since I am testing and the only person in this account it was easy to spot. Having updates come from an alternate region could pose a problem in some scenarios from a legal perspective. There are jurisdictional and regulatory reasons why some companies need to ensure all their traffic is within the region they define and use.
On top of that, the traffic is on port 80 which I presume is unencrypted (haven't looked yet). If this was all internal to AWS you might live with that, however in my last exploratory post I found out from AWS support that traffic to buckets in different regions will traverse the Internet. Since Yum updates are hosted in S3 if they went from Oregon to Southeast Asia, does that mean I'm getting my Yum updates unencrypted over the Internet? Something to look into if that was my only option but fortunately, there is a solution.
AWS support recommended a plugin called "fastestmirror" which will get you to the closest Yum repo.
To install the fastestmiror plugin:
sudo yum install yum-plugin-fastestmirror -y
change fastest mirror_enabled=0 to fastestmirror_enabled=1 in amzn-main.repo and amen-updates.repo.
sudo yum clean all
sudo yum updates -y
The plugin will help you get your updates from the correct source but if you want to be absolutely sure your updates are coming from the correct source, you'll have to set up networking rules to block the alternatives.
For more about encrypting cross-region traffic: VPNs for AWS Cross-Region Encryption