System fullimage OTA upgrade and greengrass componennt dependencies

Question

I have a system running greengrass with various components installed - including SystemManager. The upgrade is upgrading a complete system image using A/B upgrade scheme - however we preserve the greengrass install location between upgrades - so this remains untouched and available after the OTA upgrade, although the complete Kernel and root filesystem have been upgraded. I have noticed that SystemsManager does not always start cleanly after the upgrade, although when removed from the unit deployment, and then re-added it starts successfully.
Basically my question is 
* are there/can there be dependencies on greeengrass components on the base system image, for example, packagages which may be installed as part of a component deployment for example ?
* After initially being installed - how would components handle some dependencies disapearing - would they automatically re-install/deploy ?
* How would this scenario be handled in a GG environmnet - where the system can be upgraded/replaced whilst preserving the GG deployment state ?

Accepted Answer

Hi @majh,

1. Greengrass components depend on some system offerings, such as `java`. Components which you create may have more dependencies including packages installed from apt/yum for example.
2. When Greengrass starts up (or restarts), all components go through the `install` phase again before running. If a component is written properly, then it will install all that it needs to work properly at this time.
3. As long as the Greengrass root directory remains intact, Greengrass should be able to restart and operate normally.

If you're having a specific issue, please do comment with more details. But if you're just asking how things work in general, then I hope this helps.

Cheers,

Michael

System fullimage OTA upgrade and greengrass componennt dependencies

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