Fixes #36877 - Add a pre-upgrade check for katello-agent

definitions/checks/katello_agent.rb

@@ -0,0 +1,41 @@
+require 'yaml'
+
+class Checks::CheckKatelloAgentEnabled < ForemanMaintain::Check
+  metadata do
+    label :check_katello_agent_enabled
+    description 'Check whether the katello-agent feature is enabled before upgrading'
+    tags :pre_upgrade
+
+    confine do
+      !feature(:capsule)
+    end
+  end
+
+  def run
+    instance_name = feature(:instance).downstream ? "Satellite" : "Katello"
+    instance_version = feature(:instance).downstream ? "6.15" : "4.10"
+    installer_command = feature(:instance).downstream ? "satellite-installer" : "foreman-installer"
+    maintain_command = feature(:instance).downstream ? "satellite-maintain" : "foreman-maintain"
+
+    assert(
+      !katello_agent_enabled?,
+      "The katello-agent feature is enabled on this system. As of #{instance_name}"\
+      " #{instance_version}, katello-agent is removed and will no longer function."\
+      " Before proceeding with the upgrade, you should ensure that you have deployed"\
+      " and configured an alternative tool for remote package management and patching"\
+      " for content hosts, such as Remote Execution (REX) with pull-based transport."\
+      " See the Managing Hosts guide in the #{instance_name} documentation for more info."\
+      " Disable katello-agent with the command"\
+      " `#{installer_command} --foreman-proxy-content-enable-katello-agent false`"\
+      " before proceeding with the upgrade. Alternatively, you may skip this check and proceed by"\
+      " running #{maintain_command} again with the `--whitelist` option, which will automatically"\
+      " uninstall katello-agent."
+    )
+  end
+
+  private
+
+  def katello_agent_enabled?
+    feature(:installer).answers['foreman_proxy_content']['enable_katello_agent']
+  end
+end