How the engine works
A tale on computer systems, and how to work with them.
Nico Rehwaldt 2025
How does the engine work?
How does a computer work?
A computer takes instructions, and executes them.
It does not guess, it does not discuss.
It always worked that way, and when it works differently, then it is developed that way.
What does this mean for humans operating it?
When things go awry, a human is to blame.
Why would you still use a computer?
A computer only does the mistakes that you told it to do.
It executes things at scale, never gets tired.
How should a human operate a computer?
You should know what you do and why.
You want to test things, to verify your assumptions are correct.
You look to (good) tools to support you in being successful.
You follow a structured approach.
Computers are built to prevent grave consequences.
User failure: Prevent accidentally harm by confirming dangerous computations, support testing in non-critical environments.
(Rare) Computer failure: Safe-guard mission critical computation, let multiple computers do the work (i.e. on a plane).
So again, how does the [Camunda] engine work?
You model what to execute, visually, using BPMN.
Additional configuration you attach to each step tells the engine how it shall be executed.
You deploy a BPMN process to the engine, hence telling it what exactly to execute.
The engine executes what you told it to do
- When you ask it to start a process instance
- When an event happens (timer elapsed, message arrived, condition fulfilled)
- When a piece of work should be started, or completes
The engine executes without magic
- It executes what you deployed, as you specified it
- It keeps track of things:
- deployed process definitions
- running process instances
- active tasks and event subscriptions
The engine executes at scale
- It is great at waiting
- It executes fast and handles high load
Thanks
❤️
Appendix
You develop Camunda no different than you develop any other software.
It matters "where the thing runs"
Because this means different context is available.
There is many "engines"
- BPMN engine - executes BPMN inside of Camunda 8
- dmn-scala - evaluates DMN decisions inside of Camunda 8
- feel-scala - evaluates FEEL expressions inside of Camunda 8
- "feel-js" - is used in the modeling stack or browser context to evalute FEEL
Many "engines"
It matters what a Camunda developer does
- You implement an E2E process, you deliver an experience to end-users
- You implement a re-usable building block, you provide infrastructure to others
What you build for whom changes your way of working
Where a Camunda developer works matters, and so does their technical expertise
Modeler: Supporting Camunda implementation in different environments, for different personas
