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A library for (semi-)formal component specification and component monitoring
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ROPOD Component Monitoring


How to run

Run by specifying the path to a configuration file:

python3 [config_file_path]

Example: python3 config/component_monitoring_config.yaml

Note that the default value of [config_file_path] is config/component_monitoring_config.yaml.

Component monitor specification

We see monitors as functions that get a certain input and produce a component status message as an output, such that we define these mappings in YAML-based configuration files.

Based on our abstraction, each component is associated with one or more monitors which may be redundant or may look at different aspects of the component; we refer to these monitors as component monitoring modes. We classify monitoring modes into different types, in particular:

  • Existence monitors: Validate the existence of a component (e.g. whether a hardware device is recognised by the host operating system or whether a process is running)
  • Functional monitors: Validate the operation of a component, namely whether the component satisfies a predefined functional specification

The configuration file for a given component specifies a list of modes and has the following format:

component_name: string          [required] -- Component name (snake case should be used
                                              if the name has multiple words)
description: string             [required] -- Monitored component
modes: list<string>             [required] -- A list of path names to component monitor
                                              configuration files
dependencies: list<string>      [optional] -- A list of components on which the component depends
dependency_monitors: dict       [optional] -- For each dependency in "dependencies", specifies
                                              the types and names of the monitors that are
                                              of interest to the component

In modes, each file defines the input-output mapping mentioned above and has the format shown below:

name: string                                            [required] -- Monitor mode name (snake case
                                                                      should be used if the name has
                                                                      multiple words)
description: string                                     [required] -- Monitor mode description
mappings:                                               [required] -- Specified a list of functional
                                                                      input-output mappings for the
                                                                      monitor mode
    - mapping:
        inputs: list<string>                            [required] -- A list of inputs to the monitor mode
                                                                      (e.g. data variable names)
        outputs:                                        [required] -- A list of monitor outputs
            - output:
                name: string                            [required] -- Output name
                type: string                            [required] -- Output type (allowed types: bool,
                                                                      string, int, double)
                expected: bool | string | int | double  [optional] -- Expected value of the output
        map_outputs: bool                               [optional] -- Specifies whether the mapping outputs
                                                                      should be returned in a map or not
                                                                      (returning them in a map is useful if there
                                                                      may be an unknown number of output copies -
                                                                      e.g. if the number of sensors changes
arguments:                                              [optional] -- An optional dictionary of arguments to the
                                                                      monitor mode (e.g. thresholds). The arguments
                                                                      should be specified as name-value pairs
    name_n: value_n

In this specification, the optional output parameter map_outputs allows controlling the overall type of the monitor output, such that if map_outputs is set to true, the outputs will be returned in a dictionary. This is useful if the number of output value copies is unknown at design time.

Monitor output

The output produced by each component monitor is a string in JSON format which has the general format shown below:

    "component": "",
    "component_id": "",
    "component_sm_state": "",
        "monitorName": "",
        "monitorDescription": "",

For the full message description, see ropod-models

In this message:

  • if map_outputs is set to false or is not set at all, healthStatus is a list of key-value pairs of the output names specified in the monitor configuration file along with the output values corresponding to those
  • on the other hand, if map_outputs is set to true, healthStatus is a dictionary in which each value is a list of key-value pairs of the output names

Specification example

To illustrate the component monitoring configuration described above, we can consider an example in which a robot has two laser scanners whose status we want to monitor. Let us suppose that we have two monitoring modes for the scanners, namely we can monitor whether (i) the hardware devices as such are recognised by the host operating system and (ii) the scanners are operational. A configuration file for this scenario would look as follows:

name: laser_monitor
modes: [laser_monitors/device.yaml, laser_monitors/heartbeat.yaml]
dependencies: []

Referring to the two monitor modes as device and heartbeat monitors, we will have the two monitor configuration files shown below:

name: laser_device_monitor
    - mapping:
        inputs: [/dev/front_laser]
            - output:
                name: front_laser_working
                type: bool
    - mapping:
        inputs: [/dev/rear_laser]
            - output:
                name: rear_laser_working
                type: bool
name: laser_heartbeat_monitor
    - mapping:
        inputs: [/scan_front]
            - output:
                name: front_laser_working
                type: bool
    - mapping:
        inputs: [/scan_rear]
            - output:
                name: rear_laser_working
                type: bool

Laser scanner device monitor result example:

    "monitorName" : "laser_device_monitor",
    "monitorDescription" : "Monitor verifying that laser devices are recognised by the operating system",
        "hokuyo_front_working": true,
        "hokuyo_rear_working": true

Battery monitor result example:

    "monitorName" : "battery_functional_monitor",
    "monitorDescription" : "Battery level monitor",
        "battery_working": true,
        "battery_voltage": 12

Procedure for adding new monitors

Automatic procedure

This is the recommended way of adding new monitors since it creates all necessary file skeletons at once.

To add new monitors using this procedure, go to the repository's directory and run

python3 component_monitoring/utils/ [component_config_dir] \
[host_name] [monitor_type] [component_name] [mode_names]


  • [component_config_dir] is the path to the component config directory
  • [host_name] is the name of the host on which the monitors are running (either robot or black-box)
  • [monitor_type] is the type of monitor (either hardware or software)
  • [component_name] is the name of the component to be monitored
  • [mode_names] is a list of component monitor modes separated by space

The script will create:

  1. A component configuration file [component_config_dir]/[host_name]/[monitor_type]/[component_name].yaml
  2. A directory [component_config_dir]/[host_name]/[monitor_type]/[component_name] and monitor mode configuration files inside it
  3. A directory [monitor_type]/[component_name] at the location of the package component_monitoring.monitors and individual Python scripts for the monitor modes inside it

Once the necessary files are created, one simply has to complete the mode configuration files, the Python scripts of the monitor modes, and, if necessary, list dependencies in the component monitor configuration file.

Manual procedure

  1. Create a monitor configuration file component_monitoring/component_config/<host>/<type>/<component-name>.yaml, where <host> is either robot or black-box and <type> is either hardware or software depending on the type of component, and describe the monitoring modes as explained above. Make sure that the component_name parameter in the monitor configuration file is set to <component-name>
  2. Create a directory component_monitoring/component_config/<host>/<type>/<component-name> and add the mode configuration files there
  3. Create a directory component_monitoring/monitors/<type>/<component-name> and implement the mode monitors in separate scripts; the monitors should inherit from the MonitorBase class defined in Make sure that the names of the scripts in which the modes are implemented match the names specified in the mode configuration files
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