Greengrass IPC to IoT Core in low/no connectivity regions

Question

When an IoT message is sent, via IPC channel (MQTT proxy), but greengrass is not connected to the internet, are the messages discarded?

```
    accessControl:
      aws.greengrass.ipc.mqttproxy:
        com.savic.Telemetry:pub:0:
          policyDescription: Allows access to publish to telemetry topic
          operations:
            - aws.greengrass#PublishToIoTCore
          resources:
            - device/dev/telemetry/events
            - device/prod/telemetry/events

```

```
try:
        op = ipc_client.new_publish_to_iot_core()
        op.activate(model.PublishToIoTCoreRequest(
            topic_name=TELEMETRY_TOPIC,
            qos=model.QOS.AT_LEAST_ONCE,
            payload=json.dumps(message).encode(),
        ))

try:
            op.get_response().result(timeout=TIMEOUT)
        except:
            pass
```

Does GG keep them, then send them later, when there is connectivity, or is this something we have to handle in our component?

Answer

Hi Sash. There is an MQTT spooler.
https://docs.aws.amazon.com/greengrass/v2/developerguide/configure-greengrass-core-v2.html#configure-mqtt
https://docs.aws.amazon.com/greengrass/v2/developerguide/greengrass-nucleus-component.html

> spooler
(Optional) The MQTT spooler configuration for the Greengrass core device. This object contains the following information:

>maxSizeInBytes
(Optional) The maximum size of the cache where the core device stores unprocessed MQTT messages in memory. If the cache is full, the core device discards the oldest messages to add new messages.

>Default: 2621440 (2.5 MB)

>keepQos0WhenOffline
>(Optional) You can spool MQTT QoS 0 messages that the core device receives while its offline. If you set this option to true, the core device spools QoS 0 messages that it can't send while it's offline. If you set this option to false, the core device discards these messages. The core device always spools QoS 1 messages unless the spool is full.

>Default: false

Answer

Wanted to update this answer as there has been a feature release with GG V2 Version 2.11 - https://docs.aws.amazon.com/greengrass/v2/developerguide/disk-spooler-component.html

This disk spooler component , along with Nucleus configurations as specified in the above link will ensure that the MQTT messages are backedup to disk.

This will ensure that data loss is prevented in case of disconnection

Greengrass IPC to IoT Core in low/no connectivity regions

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