multipass: better error handling when images are unavailable

[mr-cal]

Overview

Sometimes the snapcraft images for multipass aren't available and produce an error when launching a multipass instance.

Details

The multipass error is launch failed: Remote "snapcraft" is unknown or unreachable.

snap restart multipass may fix the error.

You can also reproduce it with:

1. disconnecting network
2. snap restart multipass
3. multipass launch snapcraft:core22

Solution

Possible solutions:

• Before launching, run multipass find --format=yaml and confirm that the snapcraft:core... images are available.
• Try to launch, catch the exception, and parse the output for launch failed: Remote "snapcraft" is unknown or unreachable.

Either way, we should also recommend the user to restart multipass. This can be done directly in the error message or point to documentation.

Sources

• https://github.com/canonical/multipass/issues/2235
• https://forum.snapcraft.io/t/multipass-launch-failure/33808
• https://askubuntu.com/questions/1460377/launch-failed-remote-snapcraft-is-unknown-or-unreachable-multipass-returned
• https://github.com/snapcore/snapcraft/issues/4106

[mr-cal]

A similar problem was reported in launchpad: https://bugs.launchpad.net/snapcraft/+bug/2012074

This problem will occur for anyone using craft-providers on Apple silicon or arm64 hardware (raspberry pi et al.).

In this case, the problem is that the snapcraft:core[18|20|22] images are only available for amd64, whereas the developer was using arm64. So the error message or documentation should mention this caveat.

Notes:

• Only remote images that end in -disk can be used for multipass (see here that only amd64 has -disk images)
• Multipass's source code is the best source of truth for snapcraft image support