信号15是什么意思

Question

在 heroku 上部署 fastapi 应用程序后出现此错误。它说应用程序因信号 15 而终止。有人可以帮助我吗？

2021-12-03T12:17:35.623624+00:00 app[web.1]: [2021-12-03 12:17:35 +0000] [11] [INFO] Worker exiting (pid: 11)
2021-12-03T12:17:35.623625+00:00 app[web.1]: [2021-12-03 12:17:35 +0000] [12] [INFO] Worker exiting (pid: 12)
2021-12-03T12:17:36.000000+00:00 app[api]: Build succeeded
2021-12-03T12:17:36.626062+00:00 app[web.1]: [2021-12-03 12:17:36 +0000] [4] [WARNING] Worker with pid 10 was terminated due to signal 15
2021-12-03T12:17:36.629487+00:00 app[web.1]: [2021-12-03 12:17:36 +0000] [4] [WARNING] Worker with pid 9 was terminated due to signal 15
2021-12-03T12:17:36.643503+00:00 app[web.1]: [2021-12-03 12:17:36 +0000] [4] [WARNING] Worker with pid 11 was terminated due to signal 15
2021-12-03T12:17:36.715299+00:00 app[web.1]: [2021-12-03 12:17:36 +0000] [4] [INFO] Shutting down: Master
2021-12-03T12:17:36.715450+00:00 app[web.1]: [2021-12-03 12:17:36 +0000] [4] [INFO] Reason: Worker failed to boot.
2021-12-03T12:17:36.865607+00:00 heroku[web.1]: Process exited with status 3
2021-12-03T12:17:37.090747+00:00 heroku[web.1]: State changed from up to crashed