Heroku扩容时出现502 Bad Gateway错误求助

我在Heroku上运行基于Docker镜像的Django应用，架构为supervisord/nginx/gunicorn/pgbouncer。此前已解决缩容时的H13错误，但现在每次扩容都会出现大量502 Bad Gateway HTTP错误，每次约9个。

以下是Logentries中搜索status>=500得到的日志：

13 Nov 2022 12:06:49.796373 <158>1 2022-11-13T11:06:49.573611+00:00 heroku router - - at=info method=GET path="/api/v1/enums/rating-types/?show_in_gallery=True&is_user_editable=True" host=www.blenderkit.com request_id=327c9a22-b5ee-4118-90f2-283bbdae5124 fwd="xxxxxxxx,172.68.254.103" dyno=web.2 connect=0ms service=0ms status=502 bytes=697 protocol=httpsException
13 Nov 2022 12:06:49.828483 <158>1 2022-11-13T11:06:49.574134+00:00 heroku router - - at=info method=GET path="/api/v1/search/?query=+asset_type:material+order:-last_upload&dict_parameters=1&page_size=15&addon_version=3.2.0&blender_version=3.3.1&scene_uuid=8c4fa678-e970-44df-bf3d-c4db2f76da33" host=www.blenderkit.com request_id=aff26f77-00c0-4ae3-92a0-47c6caee0cb4 fwd="xxxxxxxx,172.68.210.10" dyno=web.2 connect=0ms service=0ms status=502 bytes=295 protocol=httpsException
13 Nov 2022 12:06:49.903304 <158>1 2022-11-13T11:06:49.672778+00:00 heroku router - - at=info method=HEAD path="/" host=www.blenderkit.com request_id=bad94daa-967d-4fc1-89f1-abf90e935b99 fwd="xxxxxxxx,172.70.82.185" dyno=web.2 connect=0ms service=0ms status=502 bytes=145 protocol=httpsException
13 Nov 2022 12:06:49.958305 <158>1 2022-11-13T11:06:49.748174+00:00 heroku router - - at=info method=HEAD path="/" host=www.blenderkit.com request_id=d73be07c-a9e8-4d9b-8895-5449b7c12376 fwd="xxxxxxx,162.158.170.37" dyno=web.2 connect=0ms service=0ms status=502 bytes=145 protocol=httpsException
13 Nov 2022 12:06:50.083388 <158>1 2022-11-13T11:06:49.931239+00:00 heroku router - - at=info method=GET path="/comments/api/assets-uuidasset/xxxxxxx/count/?_=1668337010" host=www.blenderkit.com request_id=c20cf157-19c5-43cd-95e9-e55b31c1c6d4 fwd="xxxx,172.70.111.52" dyno=web.2 connect=0ms service=0ms status=502 bytes=295 protocol=httpsException
13 Nov 2022 12:06:50.091396 <158>1 2022-11-13T11:06:49.740483+00:00 heroku router - - at=info method=GET path="/api/v1/enums/rating-types/?show_in_gallery=True&is_user_editable=True" host=www.blenderkit.com request_id=84ac1bee-7bdb-43c0-91a6-60a6f901bf64 fwd="xxxxxx,172.70.242.110" dyno=web.2 connect=0ms service=0ms status=502 bytes=697 protocol=httpsException
13 Nov 2022 12:06:50.099396 <158>1 2022-11-13T11:06:49.868807+00:00 heroku router - - at=info method=GET path="/api/v1/enums/rating-types/?show_in_gallery=True&is_user_editable=True" host=www.blenderkit.com request_id=1374d6d0-ca09-4f38-a45d-1d82dbb60a86 fwd="2003:c7:7f21:5f75:c0c9:bbbd:73f1:4975,172.70.242.110" dyno=web.2 connect=0ms service=0ms status=502 bytes=697 protocol=httpsException
13 Nov 2022 12:06:50.127304 <158>1 2022-11-13T11:06:49.961583+00:00 heroku router - - at=info method=HEAD path="/" host=www.blenderkit.com request_id=9a174072-f93f-4220-afb7-8378c84c0937 fwd="xxxxxx,172.71.178.99" dyno=web.2 connect=0ms service=0ms status=502 bytes=145 protocol=httpsException
13 Nov 2022 12:06:50.133395 <158>1 2022-11-13T11:06:49.99942+00:00 heroku router - - at=info method=GET path="/api/v1/enums/rating-types/?show_in_gallery=True&is_user_editable=True" host=www.blenderkit.com request_id=abb84ce4-f4c8-4226-a23f-32d7310007c8 fwd="xxxxx,172.70.242.110" dyno=web.2 connect=0ms service=0ms status=502 bytes=697 protocol=httpsException
13 Nov 2022 12:06:50.151358 <158>1 2022-11-13T11:06:49.783907+00:00 heroku router - - at=info method=GET path="/avatar-redirect/xxxxxxxxx/128/" host=www.blenderkit.com request_id=44e69bb9-2ae4-4d20-a03d-eb71a370f364 fwd="xxxxxxxxxx,172.68.66.87" dyno=web.2 connect=0ms service=0ms status=502 bytes=295 protocol=httpsException
13 Nov 2022 12:06:50.402302 <158>1 2022-11-13T11:06:50.033443+00:00 heroku router - - at=info method=HEAD path="/" host=www.blenderkit.com request_id=810db70f-8b56-404b-befb-456424aacdce fwd="xxxxxxxx,172.70.91.43" dyno=web.2 connect=0ms service=0ms status=502 bytes=145 protocol=httpsException
13 Nov 2022 12:06:55.828359 <158>1 2022-11-13T11:06:55.672729+00:00 heroku router - - at=info method=GET path="/avatar-redirect/xxxxxxxxx/128/" host=www.blenderkit.com request_id=8e090a61-7aae-466a-a22a-d2ed5947a260 fwd="xxxxx,172.71.130.55" dyno=web.4 connect=0ms service=0ms status=502 bytes=295 protocol=httpsException
13 Nov 2022 12:06:55.994399 <158>1 2022-11-13T11:06:55.618393+00:00 heroku router - - at=info method=GET path="/comments/api/assets-uuidasset/xxxxxxxx/count/?_=1668337016" host=www.blenderkit.com request_id=41af736c-c990-42fb-b39b-681a139cce9a fwd="xxxx,172.70.242.61" dyno=web.4 connect=1ms service=0ms status=502 bytes=295 protocol=httpsException

附错误日志截图和Heroku监控指标截图，寻求解决方案。

内容的提问来源于stack exchange，提问作者Petr Dlouhý