Alexa, where's my RAM?

I regularly use very small AWS EC2 instances for things like jump servers. In particular, I use both t2.nano, and t3a.nano instances running CentOS 7. These instance types are both sold as having 0.5 GB RAM.

So I was a little surprised when I took a t2.nano instance, and upgraded it to t3a.nano, and found it to have less RAM available. This was the exact same OS boot volume, so no changes in kernel or anything like that:

[rah@t2.nano ~]$ grep MemTotal /proc/meminfo 
MemTotal:         497116 kB

[rah@t3a.nano ~]$ grep MemTotal /proc/meminfo 
MemTotal:         478304 kB

That's a reduction of almost 20 MB RAM when moving to the newer platform. Normally, I wouldn't care about 20 MB, but when you're dealing with an OS running on supposedly 512 MB to start with, this reduction is not good.

So the question is, why? They're both sold as being 0.5 GB, and since it's all virtual, Amazon can allocate however much they like per instance type. If there is a valid technical reason, e.g. the same amount of RAM presents differently due to different mapping, maybe that's OK.

But this just feels slightly icky to me, as if Amazon are trying to squeeze an extra instance or two onto their next generation hypervisors, with the same physical capacity.

Amazon Lightsail network rate limited?

Amazon Lightsail is the entry-level hosted server platform provided by Amazon AWS. For $5 per month, you get a bundle including the server, storage, network, and DNS hosting for one zone. You could assemble something similar using Amazon EC2 services, but the result would cost a little more and some costs such as network bandwidth would be unpredictable because they'd be billed based on usage. In putting together the Lightsail packages, it's pretty clear that Amazon is deliberately intending to compete head-to-head with the standard Droplets from DigitalOcean.

It's "common knowledge" that the Lightsail servers are packaged versions of the EC2 t2-series servers. In this model, the $5 Lightsail server based on, and expected to provide the performance of, a t2.nano server. However, in using a bottom-tier Lightsail server for a small project, this has not been my experience. It feels like compromise have been introduced by Amazon to try and compete on cost with DigitalOcean but not cannibalize sales of fully-featured entry level AWS instances.

By design, the t2 servers are subject to CPU resource throttling based on recent usage. However, they have no issue serving multiple Megabytes per second to the network. Unfortunately this has not been my experience with the Lightsail servers. In fact, using a $5 Lightsail server, I've consistently observed outbound network throughput limited to 64 KiB/second. I've done transfers at different times of day, through http, https, and scp, and never significantly exceeded 64 KiB/second. In fact, when copying a file a few MiB in size, observed data transfer rate is a little less than 64 KiB/second because of protocol overheads.

For a cheap server, this seems like it shouldn't be a big deal - after all, you're not paying for a whole lot. However, modern web frameworks end up causing a simple page to require several hundred KiB of data to render properly, due to embedded javascript libraries, web fonts, and so on. The result is a simple Wordpress landing page without any images being accessed by one user takes 3 seconds just to load because of network rate limiting. With search engines factoring page load time in their ranking algorithms, this makes a Lightsail-hosted prototype site unlikely to do well in search rankings regardless of whatever other SEO tricks you use.

Amazon could mitigate this to some extent by making whatever rate limiting they've implemented "burstable", i.e. for the first few seconds a connection can transfer data quickly before being slowed down to ensure you don't exceed your allowance. This would make these servers much more responsive for light web serving duties. For whatever reason they seem to have chosen to use a flat rate cap instead.

If you've decided to use Amazon to host your prototype site on small servers and are considering using Lightsail, think carefully. Unless you really need the guarantee of fixed cost, the EC2 t2 series servers are likely to offer a better user experience because of much higher outbound bandwidth available, and therefore potentially better page rankings, for not much more cost.