Update modules - i1 using file input

The purpose of update modules are:

• Grow the Mender community
  • I.e. they must be very easy to write
• Cover more use cases by enabling custom application level updates
  • Example: overwrite file, install .deb, overwrite a partition
  • Non-example: Asymmetric rootfs updates

Longer-term an update module can have multiple actions, such as install, restart and rollback, but we will start with just supporting install.

In order to take a user-first approach, we will have these two reference update modules that we write before the implementation:

• /bin/sh <DATA-IN-ARTIFACT>
  • Also covers “apt-get update abc”
• dpkg -i <DATA-IN-ARTIFACT>

A easy to use design will mean that these update modules will be very short (very little extra code needed to "integrate" them into the Mender update module framework).

Iterations:

• Write reference modules
• Define new update type
  • Artifact spec & implementation
• Save headers and payload locally
  • So update module can access them
• Client support for running module’s install action

Refereces

• Update modules are described in tasks MEN-820 and MEN-1964, and this task narrows the use cases and design in order to create the first iteration.
• Slides on initial use cases and design