Write a configuration snap for COS for robotics

COS for robotics is composed of various snaps. These snaps must be configured for your robots, your needs and your setup.

In this How-To-Guide, you will learn the different steps to define your applications configuration and how to deploy them all in one snap.

This way all your COS for robotics snap services are configured with one snap.

For the rest of the guide, the presented configuration has been inspired from rob-cos-demo-configuration.

The configuration in COS for robotics

For COS for robotics snaps, the configuration is done by sharing files with a content interface.

In this How-To you will deploy all configurations in one snap and share them with one interface. This way the various snaps will pick the configurations they need.

Snaps to configure

Before starting, let’s present the snaps that are using the content interface:

cos-registration-agent

The snap expects a device.yaml file to specify device specific information to the server. This file requires the UID of the device as well as the URL of the server. Details about this file can be found on GitHub.

Additionally, the agent can upload application-specific data to the server:

• Grafana dashboards

• Foxglove layouts

• Prometheus alerts rule files

• Loki alerts rule files

rob-cos-grafana-agent

This snap is wrapping the grafana-agent in flow mode, hence a single river file is necessary under the name grafana-agent.river.

ros2-exporter-agent

This snap expects a ros2-data-exporter.yaml file to specify the ros2bags recording configurations. The YAML file is a one to one match from the snap parameters available.

foxglove-bridge

This snap expects a foxglove-bridge.yaml file to specify the bridge configurations. The YAML file is a one to one match from the foxglove-bridge configuration.

The content sharing interface

In order to have a match between what the different snaps are expecting and your configurations, you must follow the format from the content sharing interface.

Expose a content interface slot with all the configuration placed at the root of the slot’s content, as shown below:

slots:
  configuration-read:
    interface: content
    read:
      - path/to/configurations

Configuration files layout

Once the configuration is accessible to a snap, the various services are expecting the configuration files in specific locations.

All the configuration files are relative to the root of the configuration.

cos-registration-agent

.
├── device.yaml
├── foxglove_layouts
│   ├── layout1.json
│   └── layout2.json
├── grafana_dashboards
│   ├── dashboard1.json
│   └── dashboard1.json
├── loki_alert_rules
│   ├── alert1.rules
│   └── alert2.rules
└── prometheus_alert_rules
    ├── alert1.rules
    └── alert2.rules

rob-cos-grafana-agent

.
└──  grafana-agent.river

ros2-exporter-agent

.
└──  ros2-data-exporter.yaml

foxglove-bridge

.
└──  foxglove-bridge.yaml

Write the snap

Now, with a clear view of the content interface as well as the various configurations, you can start creating the snap.

Define the snapcraft.yaml

In a new directory, start by creating a snapcraft.yaml with the following content:

name: my-rob-cos-configuration
base: core24
version: git
summary: A snap for my custom configuration of the rob cos snaps.
description: |
  A snap for my configuration of the rob cos snaps on the device.

  This snap offers a custom configuration for a rob cos device.
  It also offers a content sharing interface, to allow snaps on a device that is meant
  to work with the rob cos ecosystem to easily get configured.

  It offers a slot called configuration-read that allows plugged snaps to read data
  stored in $SNAP/etc/configuration.

  Usage:

  Connect as follows:
  sudo snap connect rob-cos-snap:configuration-read my-rob-cos-configuration:configuration-read

grade: stable
confinement: strict

Add the configurations to the snap

Under the folder snap/local/configuration, add all the configuration files.

Next, append the following part to your snapcraft.yaml:

parts:
  configuration:
    plugin: dump
    source: snap/local/configuration/
    organize:
      '*': /etc/configuration/

The configurations files will now be added to your snap.

Expose the configuration with the content interface

Expose the configurations shipped in the snap by adding the content interface.

To do so, add the following to your snapcraft.yaml:

slots:
  configuration-read:
    interface: content
    read:
      - $SNAP/etc/configuration

Use the configuration snap

Before using the configuration snap, build and install it:

snapcraft
snap install my-rob-cos-configuration*.snap --dangerous

It can now be connected to the various applications you want to configure. As an example, connect it to the cos-registration-agent with:

snap connect cos-registration-agent:configuration-read my-rob-cos-configuration:configuration-read

This connection will automatically trigger the registration on the cos-registration-agent side.

You can apply the same connections to all the snaps.

Additionally, you could add more features to your configuration snap to make it smarter.

A complete example of such snap can be found on GitHub: github.com/canonical/rob-cos-demo-configuration.

You can also find a collection of example configurations for the various COS for robotics server applications on GitHub: github.com/canonical/ROB-COS-configurations.