Group memory and uptime

This demo will introduce the group node. It subscribes to multiple nodes and group for each its data and republishes on a new topic.

Let's run it:

ros2 launch dc_demos group_memory_uptime_stdout.launch.py

[component_container_isolated-1] [{"memory":{"used":71.67569732666016},"date":1677673405.921659,"uptime":{"time":96894},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.70790100097656},"date":1677673408.868847,"uptime":{"time":96897},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.72582244873047},"date":1677673411.869299,"uptime":{"time":96900},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.86643218994141},"date":1677673414.869292,"uptime":{"time":96903},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.82553863525391},"date":1677673417.869207,"uptime":{"time":96906},"run_id":"221"}]

This launchfile is a wrapper of dc_bringup/launch/bringup.launch.py which loads a custom yaml configuration

Configuration

Measurement

We collect data from 2 plugins: memory and uptime. The first every second and the latter every 3.

measurement_server:
  ros__parameters:
    measurement_plugins: ["memory", "uptime"]
    memory:
      plugin: "dc_measurements/Memory"
      group_key: "memory"
      topic_output: "/dc/measurement/memory"
      polling_interval: 1000
    uptime:
      plugin: "dc_measurements/Uptime"
      group_key: "uptime"
      topic_output: "/dc/measurement/uptime"
      polling_interval: 3000

Data is now published on 2 ROS topics: /dc/measurement/uptime and /dc/measurement/memory.

The group_key mentioned will be used by the group node to assign a key in the new dictionary

Group

This create a memory_uptime group, subscribes to /dc/measurement/memory and /dc/measurement/uptime topics and republish the result on /dc/group/memory_uptime. The sync_delay allows to wait in a 5 seconds window timeframe the data from each topic before throwing away the data if one topic does not publish it

group_server:
  ros__parameters:
    groups: ["memory_uptime"]
    memory_uptime:
      inputs: ["/dc/measurement/memory", "/dc/measurement/uptime"]
      output: "/dc/group/memory_uptime"
      sync_delay: 5.0
      group_key: "memory_uptime"
      tags: ["flb_stdout"]
      include_group_name: false

include_group_name (Optional): Will include the name of the group in the JSON, it makes it easier later on to fetch the data from your API. In this case, we can skip it since we only have one group to show.

You can also notice that the group also has a "group_key". It means a group can be part of another.

Destination

Here, we only subscribe to the /dc/group/memory_uptime topic

    flb_stdout:
      plugin: "dc_destinations/FlbStdout"
      inputs: ["/dc/group/memory_uptime"]

Console output

In the terminal, you can see the result, published every 3 seconds (see the date field), which the is timeframe defined by sync_delay and the maximum polling_interval of the measurements.

Finally, note the new dictionary uses the key defined in the group_key measurement_server plugin configuration. They are transferred through the ROS message.

[component_container_isolated-1] [{"memory":{"used":71.67569732666016},"date":1677673405.921659,"uptime":{"time":96894},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.70790100097656},"date":1677673408.868847,"uptime":{"time":96897},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.72582244873047},"date":1677673411.869299,"uptime":{"time":96900},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.86643218994141},"date":1677673414.869292,"uptime":{"time":96903},"run_id":"221"}]
[component_container_isolated-1] [{"memory":{"used":71.82553863525391},"date":1677673417.869207,"uptime":{"time":96906},"run_id":"221"}]