Snaps are self-contained application packages designed to run on any system that supports them. Each snap is a compressed SquashFS package (bearing a .snap extension), containing all the assets required by an application to run independently, including binaries, libraries, icons, etc.
Snaps are managed by snap, the command-line userspace utility of the snapd service. With the snap command, users can query the Snap Store, install and refresh (update) snaps, remove snaps, and perform many other tasks such as managing application snapshots, setting command aliases, enabling or disabling services, etc.
The EdgeX Foundry project publishes a snap named edgexfoundry, which includes all of the EdgeX core, export, security and support services, Mongo/Redis, and all of the 3rd party runtime dependencies (Consul, Vault, Kong, …). Hackathon participants should use the version from the latest/stable channel in the Snap Store, which is the 1.0.1 release (Edinburgh). See the snap’s README for details. To install from latest/stable run:
sudo snap install edgexfoundry
After installing the edgexfoundry snap view the services by issuing the snap services command.
sudo snap services edgexfoundry
Notice that after running this one simple snap install command, all of the services required to runEdgeX will have been installed and are already running in the background on your system. Note which services are enabled and which are active by running the snap services command.
Upon installation, the following EdgeX services are automatically enabled:
- cassandra (persistent storage for Kong)
- consul (aka ‘the registry’)
- core-command
- core-config-seed (one-shot)
- core-data
- core-metadata
- edgexproxy (one-shot)
- kong-daemon
- mongod
- mongo-worker (one-shot)
- pkisetup (one-shot)
- sys-mgmt-agent
- vault
- vault-worker (one-shot)
Note – some of the above services are “one-shot” services which run once and then exit. These will show up as “enabled” but “inactive”.
The following services are disabled by default:
- support-notifications
- support-logging
- support-scheduler
- export-client
- export-distro
- device-virtual
- device-random
Any disabled service can be enabled and started using snap set. For example:
sudo snap set edgexfoundry support-notifications=on
To turn a service off (thereby disabling and immediately stopping it) set the service to off:
sudo snap set edgexfoundry support-notifications=off
On install, all services in a snap have corresponding systemd service units dynamically generated by snapd, thus if enabled, each will automatically start running when the system boots.
To keep things simple for EdgeX Open the security services in the edgexfoundry snap should be disabled by running:
sudo snap set edgexfoundry security-services=off
Currently, all log files for the snaps can be found inside $SNAP_COMMON, which is /var/snap/edgexfoundry/common. Additionally, logs can be viewed using the systemd journal or snap logs. To view the logs for all services in the edgexfoundry snap use:
sudo snap logs edgexfoundry
Individual service logs may be viewed by directly specifying the service name:
sudo snap logs edgexfoundry.consul
Once the EdgeX snap has been installed and the desired services have been successfully started, we are ready to set up an application service and a device service.
As a quick test the Mosquitto snap can be installed and a test topic can be published using the mosquitto_pub command. Use the following command to install Mosquitto:
sudo snap install mosquitto
Edgex-device-mqtt is a device service which supports importing device/sensor data readings via the MQTT protocol. It requires a running MQTT broker, as well as a peer MQTT application. The device service listens on a specific topic for incoming readings which it injects into EdgeX via the device service SDKs’ asynchronous readings feature. A peer MQTT application will be provided for the hackathon which will generate a steady stream of incoming readings related to the hackathon retail scenarios. This peer application will be setup to publish multiple scenario-specific streams on different topics. The device-mqtt service configuration provides a configuration value called “IncomingTopic” which can be used to change the topic the service listens on for incoming readings. Use the following command to install edgex-device-mqtt from the stable channel:
sudo snap install edgex-device-mqtt
After installation, check the status of the edgex-device-mqtt device service:
sudo snap services edgex-device-mqtt
Notice that the edgex-device-mqtt device service is disabled and inactive. This was done intentionally as the configuration and device profile need to be specific to each installation. You’ll find the configuration and device profile in the writable area of the snap (aka $SNAP_DATA):
/var/snap/edgex-device-mqtt/current/config/device-mqtt/res
After making the necessary modifications to configuration.toml (e.g. setting the “IncomingTopic” or changing “Port”) and mqtt.test.device.profile.yml (e.g. modifying device-resources, device-commmands, or core-commands), start and enable edgex-device-mqtt like this:
sudo snap start --enable edgex-device-mqtt
You should now be ready to receive peer MQTT application readings.
Now let’s publish a topic with a randfloat32 value of 1.2:
mosquitto_pub -t DataTopic -m '{"name":"MQTT test device","cmd":"randfloat32","randfloat32":"1.2"}'
You can check the readings from core-data with the following command:
curl -s localhost:48080/api/v1/reading | jq
Note – jq is a lightweight and flexible command-line JSON processor. In its simplest form with no command-line arguments specified, it simply outputs JSON its been given in a human-readable format. If not available on your system, it can be installed using sudo snap install jq.
If you see something similar to the following output then edgex-device-mqtt is working correctly. Float values are encoded base64 by default. The value “P5mZmg==” is 1.2 in base64.
[
{
"id": "4f922fd7-5c0d-48e0-8a06-6218d4c05fa9",
"created": 1568926981304,
"origin": 1568926981290,
"modified": 1568926981304,
"device": "MQTT test device",
"name": "randfloat32",
"value": "P5mZmg=="
}
]Once the device service has been started the configuration information is now in Consul. If you need to make further modifications to either the configuration or device profile, you’ll need to make the modifications in Consul which can be accessed from a browser at http://localhost:8500. After making modifications in Consul, the device service needs to be restarted like this:
sudo snap restart edgex-device-mqtt
If you would like to manage your EdgeX instance using a web browser, adding devices, device profiles, as well as visualizing data sent through the export service, you can do this through the EdgeX Web management UI. To install the edgex-ui-go snap run the following:
sudo snap install edgex-ui-go --channel=latest/beta
Now navigate with your browser to http://localhost:4000. The default user credentials are username: admin password:admin. Add your gateway and you’re ready to manage your EdgeX instance through the web UI.
Extending EdgeX
This section gives some hints as to how you can build your hackathon entry by creating or using additional EdgeX services.
App-Service-Configurable
Edgex-App-Service-Configurable – this is a new snap built from the current development release of EdgeX (Fuji). It allows a variety of use cases to be met by simply providing configuration (vs. writing code). For more information about this service, please refer to the README. As with device-mqtt, this service is disabled when first installed, as it requires configuration changes before it can be run. As with the device-mqtt snap, the configuration.toml file is found in the snap’s writable area:
/var/snap/edgex-app-service-configurable/current/config/res/
Profiles
In additional to base configuration.toml in this directory, there are a number of sub-directories that also contain configuration.toml files. These sub-directories are referred to as profiles. The service’s default behavior is to use the configuration.toml file from the /res directory. If you want to use one of the profiles, use the snap set command to instruct the service to read its configuration from one of these sub-directories. For example, to use the push-to-core profile you would run:
$ sudo snap set edgex-app-service-configurable profile=push-to-core
In addition to instructing the service to read a different configuration file, the profile will also be used to name the service when it registers itself to the system.
Note, as this service is based on the latest development release of EdgeX, not all use cases are supported, in particular integration with the EdgeX rules-engine will not work when used in conjunction with the Edinburgh release of EdgeX. Perform the following steps to install the edgex-app-service-configurable application service using the mqtt-export-configuration example and Mosquitto to test:
sudo snap install edgex-app-service-configurable
sudo snap set edgex-app-service-configurable profile=mqtt-export
sudo snap start --enable edgex-app-service-configurable.app-service-configurable
mosquitto_sub -t "edgex-events"
Multiple Instances
Multiple instances of edgex-app-service-configurable can be installed by using snap Parallel Installs. This is an experimental snap feature and must be first be enabled by running this command:
sudo snap set system experimental.parallel-instances=true
Now you can install multiple instances of the edgex-app-service-configurable snap by specifying a unique instance name when you install the snap. The instance name is made of the name of the snap plus a unique suffix which starts with the character “_”. This name only needs to be specified for the second and susbequent instances of the snap.
sudo snap install edgex-app-service-configurable edgex-app-service-configurable_http
or
sudo snap install edgex-app-service-configurable edgex-app-service-configurable_mqtt
Note – you must ensure that any configuration values that might cause conflict between the multiple instances (e.g. port, log file path, …) must be modified before enabling the snap’s service.
New Application or Device Services
Participants can also choose to construct their entry by building new device services (using the device SDKs) or new application services (using the application SDK). As the hackathon is time-boxed, most participants may just build new services natively vs. choosing to create Docker containers and/or snaps. For those interested in creating snaps for their new services, the following services can be useful as templates:
- edgex-device-mqtt (snapcraft.yaml)
- edgex-device-modbus (snapcraft.yaml)
- edgex-app-service-configurable (snapcraft.yaml)
