Describes the cause and action for error messages.
Error Message(English)：
error 503 backend is unhealthy
HTTP Error 503: Backend is unhealthy on Debian 8 ・ Issue ... - GitHub
https://github.com/certbot/certbot/issues/6494
Can't download brew installer from server ・ Issue #126 ... - GitHub
https://github.com/Homebrew/install/issues/126
Ask HN: Are github pages down? | Hacker News
https://news.ycombinator.com/item?id=7130624
Common 503 errors - Debugging | Fastly Help Guides
https://docs.fastly.com/guides/debugging/common-503-errors
Timeout errors
https://docs.fastly.com/guides/debugging/common-503-errors#timeout-errors
Origin health errors
https://docs.fastly.com/guides/debugging/common-503-errors#origin-health-errors
Connection limit errors
https://docs.fastly.com/guides/debugging/common-503-errors#connection-limit-errors
www.python.org - Backend is unhealthy - python.org Mailing Lists
https://mail.python.org/pipermail/python-list/2015-May/690248.html
Lets'Encrypt v0.28.0 stopped working on Debian 8 - Server - Let's ...
https://community.letsencrypt.org/t/letsencrypt-v0-28-0-stopped-working-on-debian-8/77138