peer_discovery_backend requires module name specified (at least for Consul)

[tj90241]

Compiled 3.10.12 from source and configured it for use with the Consul discovery plugin per documentation, which states:

"To use Consul for peer discovery, set the cluster_formation.peer_discovery_backend to consul or its module name, rabbit_peer_discovery_consul"

So, this should work:

{rabbit, [
  {cluster_formation, [
    {peer_discovery_backend, consul},
    {consul, [
...

However, when booting rabbitmq-server, it failed with:

BOOT FAILED
===========
Exception during startup:

error:undef

    consul:supports_registration/0
        args: []
    rabbit_peer_discovery:maybe_register/0, line 124
    rabbit_mnesia:init/0, line 82
    rabbit_boot_steps:-run_step/2-lc$^0/1-0-/2, line 41
    rabbit_boot_steps:run_step/2, line 48
    rabbit_boot_steps:-run_boot_steps/1-lc$^0/1-0-/1, line 19
    rabbit_boot_steps:run_boot_steps/1, line 20
    rabbit:start/2, line 906

Kernel pid terminated (application_controller) ({application_start_failure,rabbit,{undef,{rabbit,start,[normal,[]]}}})

Crash dump is being written to: /var/log/rabbitmq/erl_crash.dump...done

So clearly, it can't find the plugin. Which led me to make no other changes to my configuration, other than changing peer_discovery_backend to the module name (rabbitmq_peer_discovery_consul). This worked, and there was no more error:undef thrown for consul:supports_registration/0.

[tj90241]

The configuration schema also seems to be namespaced differently?

I'm groking: https://www.rabbitmq.com/cluster-formation.html

which says e.g.:

cluster_formation.peer_discovery_backend = consul

cluster_formation.consul.host = consul.eng.example.local
cluster_formation.consul.acl_token = acl-token-value

However, I had to namespace everything like this based on the source code, which worked:

{rabbit, [
  {cluster_formation, [
    {peer_discovery_backend, rabbitmq_peer_discovery_consul},
    {peer_discovery_consul, [
      {consul_host, "consul.service.consul.<REDACTED>"},
      {consul_acl_token, "<REDACTED>"},
      {consul_port, 8501},
      {consul_scheme, https},
      {consul_ssl_options, [
        {cacertfile, "/etc/rabbitmq/ssl/consul_chain.pem"},
        {certfile,   "/etc/rabbitmq/ssl/consul_cert.pem"},
        {keyfile,    "/etc/rabbitmq/ssl/consul_privkey.pem"}
      ]},
      {consul_svc, rabbitmq},
      {consul_svc_addr_auto, false},
      {consul_svc_addr, "<REDACTED>"},
      {consul_use_longname, true}

except consul_ssl_options -- those don't seem to be respected, anymore after having been added in 8f8a138