During the codfw kubernetes upgrade (T397148), thumbor was not depooled by the cookbook (as it does not have a discovery entry in service catalog). Depooling it would not have helped though, since we hardcode codfw thumbor in the swift config:
hieradata/codfw/profile/swift/proxy.yaml:profile::swift::proxy::thumborhost: 'thumbor.svc.codfw.wmnet:8800' hieradata/codfw/profile/swift/proxy.yaml:profile::swift::proxy::inactivedc_thumborhost: 'thumbor.svc.eqiad.wmnet:8800'