Going full SOA has unarguable benefits, but the steep startup cost and need for excessive forward planning goes against the agile mentality of strictly necessary, small, incremental changes. At Lumosity, we've developed a set of best practices using engines to entirely divide behavior and responsibility by wrapping new services within well-defined, small Ruby APIs. This technique obviates the need for complex network (HTTP) APIs with their well-known problems of maintenance and testing. Get rid of spaghetti code without diving into the deep end of recorded responses and fake servers. Later, if the architecture demands a separate service, the engine will already have an API fully defined and ready to port over from Ruby to HTTP.