When any resource is requested with a "?graph=true" parameter, it engages the pycallgraph object to start tracking, stopping at the end of the processing and then exports a .png of the callgraph to the CALLGRAPH_DIR (or "ROOT_DIR/callgraphs" if CALLGRAPH_DIR is not set).

It adds the requisite dependencies to the Dockerfile:
        apt-get install graphviz
        pip install pycallgraph