AWS yum does not work from private subnet (does work from public)

Solution 1:

In a very similar situation as the one described in the question I was able to solve it by adding the proxy configuration to /etc/yum.conf.

Like this:

echo "proxy=http://my.proxy.internal:3128/" >> /etc/yum.conf

Solution 2:

If the Private Subnet is not connected to the internet, then ofcourse you can not access the internet to install any package.

You can also launch an instance in Public Subnet, and after installing required packages, just create a custom Image of it, which you can easily use while launching the instance in any Subnet, regardless of if it has internet access or not.