Zuul contains Ansible modules and plugins to control the execution of Ansible Job content. These break down into two basic categories.
- Restricted Execution on Executors
- Build Log Support
ansible-playbook on executors to run job content on nodes. While the intent is that content is run on the remote nodes, Ansible is a flexible system that allows delegating actions to
localhost, and also reading and writing files. These actions can be desirable and necessary for actions such as fetching log files or build artifacts, but could also be used as a vector to attack the executor.
For that reason Zuul implements a set of Ansible action plugins and lookup plugins that override and intercept task execution during untrusted playbook execution to ensure local actions are not executed or that for operations that are desirable to allow locally that they only interact with files in the zuul work directory.
Build Log Support
Zuul provides realtime build log streaming to end users so that users can watch long-running jobs in progress. As jobs may be written that execute a shell script that could run for a long time, additional effort is expended to stream stdout and stderr of shell tasks as they happen rather than waiting for the command to finish.
Zuul contains a modified version of the :ansiblecommand that starts a log streaming daemon on the build node.
All jobs run with the :pyzuul.ansible.callback.zuul_stream callback plugin enabled, which writes the build log to a file so that the :pyzuul.lib.log_streamer.LogStreamer can provide the data on demand over the finger protocol. Finally, :pyzuul.web.LogStreamingHandler exposes that log stream over a websocket connection as part of :pyzuul.web.ZuulWeb.
In addition to real-time streaming, Zuul also installs another callback module, :pyzuul.ansible.callback.zuul_json.CallbackModule that collects all of the information about a given run into a json file which is written to the work dir so that it can be published along with build logs. Since the streaming log is by necessity a single text stream, choices have to be made for readability about what data is shown and what is not shown. The json log file is intended to allow for a richer more interactive set of data to be displayed to the user.