Elixir warning when locale is not UTF-8

[wyardley]

When certain locale settings are not UTF-8, rabbitmqctl returns a warning (even with the -q option).

This has caused problems with config management software that calls the shell commands and parses the output; while this can be fixed, is UTF-8 actually required? Forcing the env to a specific locale seems a bit drastic, so I wonder if there's a way to suppress this warning, especially when -q is used.
voxpupuli/puppet-rabbitmq#671
saltstack/salt#45383

• RabbitMQ version: 3.7.4-1
• Erlang version: 20.3-1
• RabbitMQ plugin information via rabbitmq-plugins list

 Configured: E = explicitly enabled; e = implicitly enabled
 | Status: * = running on rabbit@ubuntu-server-1604-x64
 |/
[  ] rabbitmq_amqp1_0                  3.7.4
[  ] rabbitmq_auth_backend_cache       3.7.4
[  ] rabbitmq_auth_backend_http        3.7.4
[  ] rabbitmq_auth_backend_ldap        3.7.4
[  ] rabbitmq_auth_mechanism_ssl       3.7.4
[  ] rabbitmq_consistent_hash_exchange 3.7.4
[  ] rabbitmq_event_exchange           3.7.4
[  ] rabbitmq_federation               3.7.4
[  ] rabbitmq_federation_management    3.7.4
[  ] rabbitmq_jms_topic_exchange       3.7.4
[E*] rabbitmq_management               3.7.4
[e*] rabbitmq_management_agent         3.7.4
[  ] rabbitmq_mqtt                     3.7.4
[  ] rabbitmq_peer_discovery_aws       3.7.4
[  ] rabbitmq_peer_discovery_common    3.7.4
[  ] rabbitmq_peer_discovery_consul    3.7.4
[  ] rabbitmq_peer_discovery_etcd      3.7.4
[  ] rabbitmq_peer_discovery_k8s       3.7.4
[  ] rabbitmq_random_exchange          3.7.4
[  ] rabbitmq_recent_history_exchange  3.7.4
[  ] rabbitmq_sharding                 3.7.4
[  ] rabbitmq_shovel                   3.7.4
[  ] rabbitmq_shovel_management        3.7.4
[  ] rabbitmq_stomp                    3.7.4
[  ] rabbitmq_top                      3.7.4
[  ] rabbitmq_tracing                  3.7.4
[  ] rabbitmq_trust_store              3.7.4
[e*] rabbitmq_web_dispatch             3.7.4
[  ] rabbitmq_web_mqtt                 3.7.4
[  ] rabbitmq_web_mqtt_examples        3.7.4
[  ] rabbitmq_web_stomp                3.7.4
[  ] rabbitmq_web_stomp_examples       3.7.4

• Client library version (for all libraries used)
• Operating system, version, and patch level: Ubuntu 1604-x64

root@ubuntu-server-1604-x64:~# locale
LANG=C
LANGUAGE=C
LC_CTYPE="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=
root@ubuntu-server-1604-x64:~# rabbitmqctl list_users
warning: the VM is running with native name encoding of latin1 which may cause Elixir to malfunction as it expects utf8. Please ensure your locale is set to UTF-8 (which can be verified by running "locale" in your shell)

[michaelklishin]

This is an Elixir requirement, not that of RabbitMQ CLI tools (which are in https://github.com/rabbitmq/rabbitmq-cli, by the way).

There are no plans to switch away from using Elixir for CLI tools.

[michaelklishin]

Configuration software that uses CLI tools can override locale environment variables for the calls that where parsing the output is warranted:

LANG="en_US.UTF-8" LC_ALL="en_US.UTF-8" rabbitmqctl …

as a workaround. We will consider forcing this in our shell scripts (filed #1573 for that with a more specific problem statement) but IIRC this has been considered before and rejected.