This is what we built at Netflix and called latency monkey. It turns out determining that a downstream service is slow is a lot harder than determining if it's

This is what we built at Netflix and called latency monkey. It turns out determining that a downstream service is slow is a lot harder than determining if it's unavailable, so it was an important way for us to test how services handle slowdowns and network problems as well. It was really simple, it just dropped some configureable percentage of packets, which would force a resend, causing the other side to get packets delayed and out of order. It ended up finding a lot of problems in our error handling code for network access.