Contents
nodehealth.py contains a HealthMonitor class that continuously monitors the
operational health of the node computer and take steps to recover from failures.
It also contains functions such as send_heartbeat that allow the hub, the
librarian or other programs to externally monitor system health.
There are a number of tests that can be performed that check on the operational status of imagehub and other parts of the distributed system that it is a part of:
- Wifi strength & selection of strongest known wifi hub
- Network ping OK
- Communications with imagehub via imagezmq OK
- Before starting imagenode.py, check that no imagenode.py is already running
- Check that some processes take "normal" amount of time; sometimes ssh takes 45 seconds to respond; indicates issues like marginal SD card
- On RPi, check integrity of SD card occasionally (how?)
How a hub needs to recover from a problem varies, depending on what type of system the hub is running on.
Recovery options include:
- restarting the ZMQ connection context
- stopping and restarting the system wifi service
- connecting to a different wifi network
- restarting the imagehub.py program
The current nodehealth.py module is mostly a stub awaiting the results of ongoing testing of different methods of implementing the above listed recovery options.
Return to How imagenode works. or Return to main documentation page README.rst.