Over time, jobs start taking long enough to the point where you need to split them. Separate jobs are assigned slices of the original batch. Eventually, there are so many slices that you make a Jenkins job where the sole responsibility is firing off these individual jobs.

Then you start hitting the real painpoints in Jenkins. Poor allocation of jobs across your nodes/agents, often overloading CPU/Mem on machines, and you struggle to manage the ungodly interface that is the Jenkins REST endpoint. You install many Jenkins addons to try and address the scheduling problems, and end up with a team dedicated to managing this Jenkins infrastructure.

The scaling struggles continue to amass and you end up needing separate Jenkins instances to battle the load. Any attempt at replacing the Jenkins infrastructure goes on standstill, as the amount of random scripts found in Jenkinsfiles has created an insurmountable vendor lock-in.

You read a post about a select-for-update job scheduler and reflect on simpler times. You cry as you refactor your Jenkins Groovy DSL.

The danger is that it's so easy to start and it's decent for small and simple applications. Once your jobs start growing, both in number of contributors and in workload, the problems start. DSL is difficult to debug, plugins are buggy and the brittle master node will become your most precious pet that need constant supervising to not grind the whole system to a stop. By the time you realize this you have a hard time to get out of this lockin.