This definitely looks like the leak:
6463 @ 0x43159b 0x431643 0x408cee 0x408a1b 0xae7d38 0x45fa61 # 0xae7d37 github.com/juju/juju/vendor/gopkg.in/natefinch/lumberjack%2ev2.(*Logger).millRun+0x57 /workspace/_build/src/github.com/juju/juju/vendor/gopkg.in/natefinch/lumberjack.v2/lumberjack.go:379
This definitely looks like the leak:
6463 @ 0x43159b 0x431643 0x408cee 0x408a1b 0xae7d38 0x45fa61 com/juju/ juju/vendor/ gopkg.in/ natefinch/ lumberjack% 2ev2.(* Logger) .millRun+ 0x57 /workspace/ _build/ src/github. com/juju/ juju/vendor/ gopkg.in/ natefinch/ lumberjack. v2/lumberjack. go:379
# 0xae7d37 github.