A traditionally designed CI server distributes tasks to other machines on the network, each of which has been configured with the OS, tools, and credentials that tasks need to perform their work. Each task executes in the runtime environment of a machine.
Pipelines can, when explicitly directed, execute any step this way, running it directly on the host build node in the runtime of its machine image. This may be appropriate when you need to perform a task from the baseline environment of the machine.
 |
While efficient, executing directly on the host is very inflexible. If the task requires another tool on the VM, the task must either load it itself or a systems administrator must configure it for the developer in advance. When an organization needs to support many teams, staging environments, and DevOps activities, this can quickly become difficult and expensive to manage. Also, changes made to the host VM will persist for future steps running on the same host, leading to unpredictability.