The article's conclusion -- that Lambda is cheaper than EC2 instances for this use case -- is completely wrong. The author only counted the per-request overhead, and neglected to add the actual cost of the GB-hours consumed. If each container uses 512MB of memory, then keeping one request running at a time for an entire month costs about $22. For comparison, a t2.nano instance with the same amount of memory costs $4/month.
Lambda is a value-added service on top of EC2. It only makes financial sense to use it when you don't want something running constantly, or otherwise have a way to take advantage of the extremely fine granularity in billing. (Or if you're willing to pay a premium to have Amazon manage your process lifecycles for you.)
$4/mo doesn't include the cost of monitoring and maintenance that come with running your own instance. When you can't amortize those costs across a large fleet of instances, Lambda is often much cheaper when looking at the total cost. Also, to get anywhere near the same reliability expectations, you'd need at least 2 instances and an ELB. Granted that will be able to handle a lot more traffic, but it's still not fair to compare Lambda to a single instance.
You would also need to include a messaging queue infrastructure as lambda offers a dead letter queue. So that will require a few more RabbitMQ ec2 boxes in cluster mode.
Lambda is a value-added service on top of EC2. It only makes financial sense to use it when you don't want something running constantly, or otherwise have a way to take advantage of the extremely fine granularity in billing. (Or if you're willing to pay a premium to have Amazon manage your process lifecycles for you.)