Build fails when multiple run-on are specified

[seb4stien]

Bug Description

The charmcraft build command fails when charmcraft.yaml contains the following configuration:

bases:
  - build-on:
    - name: ubuntu
      channel: "22.04"
    run-on:
    - name: ubuntu
      channel: "22.04"
    - name: "ubuntu"
      channel: "20.04"

In the logs we can see that charmcraft is generating a hostname that contains understores:

2025-01-31 15:16:50.027 Setting charmcraft to be injected from the host into the build environment because it is running as a snap.
2025-01-31 15:16:50.027 Preparing managed instance 'charmcraft-digest-squid-auth-helper-ubuntu-22.04-amd64_ubuntu-20.04-amd64-5603827'
2025-01-31 15:16:50.031 Using hostname 'charmcraft-digest-squid-auth-helper-ubuntu-2204-amd64_ubuntu-2'

This generates an error as '_' are not valid characters for the hostname command:

2025-01-31 15:17:01.013 Executing in container: lxc --project charmcraft exec local:charmcraft-digest-squid-auth-helper-ubun-5e15c5547ad997b04c08 -- env CRAFT_MANAGED_MODE=1 CHARMCRAFT_MANAG
ED_MODE=1 DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true DEBIAN_PRIORITY=critical hostname -F /etc/hostname
2025-01-31 15:17:01.383 Failed to set hostname.

A proposal to solve the issue here: canonical/craft-providers#722

To Reproduce

Create a charm with multiple "run-on" destinations (see charmcraft.yaml) and try to build it.

Environment

Building on Ubuntu 24.04

charmcraft.yaml

bases:
  - build-on:
    - name: ubuntu
      channel: "22.04"
    run-on:
    - name: ubuntu
      channel: "22.04"
    - name: "ubuntu"
      channel: "20.04"

Relevant log output

2025-01-31 15:16:50.027 Setting charmcraft to be injected from the host into the build environment because it is running as a snap.
2025-01-31 15:16:50.027 Preparing managed instance 'charmcraft-digest-squid-auth-helper-ubuntu-22.04-amd64_ubuntu-20.04-amd64-5603827'
2025-01-31 15:16:50.031 Using hostname 'charmcraft-digest-squid-auth-helper-ubuntu-2204-amd64_ubuntu-2'
...
2025-01-31 15:17:01.013 Executing in container: lxc --project charmcraft exec local:charmcraft-digest-squid-auth-helper-ubun-5e15c5547ad997b04c08 -- env CRAFT_MANAGED_MODE=1 CHARMCRAFT_MANAG
ED_MODE=1 DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true DEBIAN_PRIORITY=critical hostname -F /etc/hostname
2025-01-31 15:17:01.383 Failed to set hostname.

[syncronize-issues-to-jira]

Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-4077.

This message was autogenerated

[lengau]

Hi, thanks for the report! I see where this is coming from and I think we can fix it fairly simply.