description and architecture

Worker.md

@@ -1,8 +1,24 @@
 # Worker
 
 ## Description
+**Worker's** main role is securely execute given submission and possibly _evaluate_ results against model solutions provided by submitter. **Worker** is logicaly divided into two parts:
+- **Listener** - listens and communicates with **Broker** through [ZeroMQ](http://zeromq.org/). It receives new jobs, communicates with **Evaluator** part and sends back results or progress.
+- **Evaluator** - gets jobs to evaluate from **Listener** part, evaluate them (possibly in sandbox) and get to know to other part that evaluation ended. This part also communicates with **Fileserver**, downloads needed files and uploads detailed results.
+
+**Worker** after getting evaluation request has to:
+
+- Download the archive containing submitted source files and configuration file
+- Download any supplementary files based on the configuration file, such as test 
+  inputs or helper programs (This is done on demand, using a `fetch` command
+  in the assignment configuration)
+- Evaluate the submission accordingly to job configuration
+- During evaluation progress states can be sent back to **Broker**
+- Upload the results of the evaluation to the **Fileserver**
+- Notify **Broker** that the evaluation finished
 
 ## Architecture
+Picture below is overall internal architecture of worker which shows its defined classes with private variables and public functions. Vector version of this picture is available [here](https://github.com/ReCodEx/GlobalWiki/raw/master/images/Worker_Internal_Architecture.pdf).
+![Internal Worker architecture](https://github.com/ReCodEx/GlobalWiki/blob/master/images/Worker_Internal_Architecture.png)
 
 ## Installation