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.)