Optimizing execution and designing for horizontal scalability are both cases of premature optimization. Scaling vertically via hardware as much as possible is I

Optimizing execution and designing for horizontal scalability are both cases of premature optimization. Scaling vertically via hardware as much as possible is IMO the most developer-time saving way. Once that's exhausted you'll have to decide which one is easier. The biggest mistake I see is people spending a lot of time designing for horizontal scalability and then running a cluster of under-powered servers when a single powerful machine would do just fine. There are very few things that are easier in a cluster (uptime perhaps?) and many that are easier on a single machine. Once you add the requirement of having to work in a cluster, every new feature will have to respect that. If your system is doing anything interesting you'll be hitting all the distributed computing dilemmas pretty fast.