Joonos system manager

Introduction

The system manager is a service whose primary tasks are:

• Obtain per-node certificates which then can ben used to authenticate Joonos nodes to an MQTT server.
• Download and apply system updates

In addition to these, the tool features some limited telemetry features.

Development of the program is hosted on Github

Design decisions

Layer over MQTT

This arises from the idea of reusing some infrastructure in use cases where MQTT is used anyway.

It might be reasonably simple to add some other mechanism directly over TLS.

JSON over MQTT in early messages

Some other representations for data are more efficient and possibly more robust as well, but at least in the initial stages JSON has some advantages that stem from its convenient extensibility.

Another thing convenient about JSON-formatted messages is that they can easily be produced with a generic text editor and sent e.g. with mosquitto_pub.

Implement in Go

Go is not necessarily the prettiest programming language in existence, but it is one option that meets these:

• Pointer arithmetic is not an essential tool in string manipulation
• Has pretty good support in Yocto
• Program + runtime (if any) does not take too much storage space
• Executing the program takes no more than few tens of MiB of RAM

Subcommands instead of multiple executables

To support experimentation and potential additional use cases, the repository needs to be able to provide multiple commands.

Most of the extra functionality does not add much code. Placing these alternative modes into separate executables would make the space needed for the main functionality slightly smaller, but adding a second mode of operation would lead to additional executables which then would need to bundle the Go runtime, or at least the libraries for MQTT connectivity.

Deploying as a single executable is also convenient from point of view of writing bitbake recipes or other deployment tooling.

Include at least a minimal certificate authority

This may help with automated testing, at least. The mechanism is simple enough that a more complete implementation can be written separately.