machine 2.0 schema check failed: hardware_info: expected map, got nothing

[Felipe Reyes]

When trying to add a new machine (in ready state in maas) to the juju model using `juju add-unit --to foo.maas ubuntu`, the machine stays in pending state

$ juju show-machine 31
model: XXXX
machines:
  "31":
    juju-status:
      current: pending
      since: 02 Mar 2023 15:06:49Z
    instance-id: pending
    machine-status:
      current: pending
      since: 02 Mar 2023 15:06:49Z
    modification-status:
      current: idle
      since: 02 Mar 2023 15:06:49Z
    series: focal
    constraints: arch=amd64

According to the logs, juju is receiving a response from maas that's missing the hardware info section, this is a violation to the schema as its defined by juju at https://github.com/juju/gomaasapi/blob/v2/machine.go#L528

Our maas is a fairly old installation that has been receiving upgrades over time:

$ stat /var/log/installer/status
  File: '/var/log/installer/status'
  Size: 55916 Blocks: 112 IO Block: 4096 regular file
Device: 801h/2049d Inode: 13107220 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2017-06-06 11:22:43.380602193 +0000
Modify: 2012-07-21 03:10:24.874111020 +0000
Change: 2012-07-21 03:10:24.874111020 +0000
 Birth: -

[Environment]

juju 2.9.35
MAAS version: 2.3.7 (6529-g49c39fc-0ubuntu1)

Relevant log:

machine-0: 17:19:51 DEBUG juju.worker.dependency "compute-provisioner" manifold worker started at 2023-03-02 17:19:51.459753609 +0000 UTC
machine-0: 17:19:54 DEBUG juju.worker.dependency "compute-provisioner" manifold worker stopped: processing updated machines: getting all instances from broker: machine 0: machine 2.0 schema check failed: ha
rdware_info: expected map, got nothing
stack trace:
hardware_info: expected map, got nothing
github.com/juju/gomaasapi/v2.machine_2_0:550: machine 2.0 schema check failed: hardware_info: expected map, got nothing
github.com/juju/gomaasapi/v2.readMachineList:500: machine 0
github.com/juju/gomaasapi/v2.(*controller).Machines:374:
github.com/juju/juju/provider/maas.(*maasEnviron).instances2:1695:
github.com/juju/juju/worker/provisioner.(*provisionerTask).populateMachineMaps:375: getting all instances from broker
github.com/juju/juju/worker/provisioner.(*provisionerTask).processMachines:337:
github.com/juju/juju/worker/provisioner.(*provisionerTask).loop:225: processing updated machines
machine-0: 17:19:54 ERROR juju.worker.dependency "compute-provisioner" manifold worker returned unexpected error: processing updated machines: getting all instances from broker: machine 0: machine 2.0 schem
a check failed: hardware_info: expected map, got nothing

[Juan M. Tirado (tiradojm)]

Compatibility was probably broken here https://github.com/juju/gomaasapi/commit/cd944ef8b321681e529c369491902e1a9f30f892

[Simon Richardson (simonrichardson)]

PR to allow hardware info to be optional: https://github.com/juju/gomaasapi/pull/99

[Simon Richardson (simonrichardson)]

See Juju PR that brings in the gomaasapi changes https://github.com/juju/juju/pull/15312