rabbitmq plugin 1.19.1 api/federation-links failure

[pabigot]

Relevant telegraf.conf:

# Reads metrics from RabbitMQ servers via the Management Plugin
[[inputs.rabbitmq]]
  queues = ["collate", "influxdb.write", "wsn.asrpdu", "wsn.signal"]
  exchanges = ["amq.topic", "influxdb", "openweather", "tasmota", "wsn"]
  queue_name_exclude = ["amq.gen-*", "mqtt-subscription-DVES_*"]

System info:

central20[7]$ uname -a
Linux central20 5.4.0-77-generic #86-Ubuntu SMP Thu Jun 17 02:35:03 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
central20[8]$ dpkg -l | grep telegraf
ii  telegraf                             1.19.1-1                                    amd64        Plugin-driven server agent for reporting metrics into InfluxDB.
central20[9]$ cat /etc/os-release 
NAME="Ubuntu"
VERSION="20.04.2 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.2 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

Steps to reproduce:

Update from telegraph 1.19.0 to 1.19.1

Expected behavior:

Removal of unmarshal errors due to incorporation of #9443

Actual behavior:

While #9443 fixed part of the problem, #9383 (comment) notes that /api/federation-links in at least some installations does not exist, a problem that was masked by the unmarshal bug. My installation is now repeatedly complaining:

Jul 11 02:59:40 central20 telegraf[1353]: 2021-07-11T02:59:40Z E! [inputs.rabbitmq] Error in plugin: getting "/api/federation-links" failed: 404 Not Found
Jul 11 02:59:50 central20 telegraf[1353]: 2021-07-11T02:59:50Z E! [inputs.rabbitmq] Error in plugin: getting "/api/federation-links" failed: 404 Not Found

[pabigot]

It appears #6283 is based on an expectation that the federation plugin is enabled, although the module is opt-in (and not useful in a single-broker installation). There seems to be no way to opt out of attempting to collect the data, or to indicate that absence of the plugin is not an error.

What's the right solution? @jacquesh?

[pabigot]

This problem can be worked around as described in #9505 (comment)