Today my server experienced an outage and restarted automatically. However, my blog didn’t go online after that. With a little invesitgation it immediately got obvious that the nginx failed to start on first try of systemctl:

Jun 20 00:00:51  systemd[1]: Starting A high performance web server and a reverse proxy server...
Jun 20 00:00:33  nginx[814]: nginx: [warn] "ssl_stapling" ignored, host not found in OCSP responder "r3.o.lencr.org" in the certificate ">
Jun 20 00:00:14  nginx[814]: nginx: [warn] "ssl_stapling" ignored, host not found in OCSP responder "r3.o.lencr.org" in the certificate ">
Jun 20 00:00:21  systemd[1]: nginx.service: start-pre operation timed out. Terminating.
Jun 20 00:00:21  systemd[1]: nginx.service: Control process exited, code=killed, status=15/TERM
Jun 20 00:00:21  systemd[1]: nginx.service: Failed with result 'timeout'.
Jun 20 00:00:21  systemd[1]: Failed to start A high performance web server and a reverse proxy server.

The root cause seemed to be a temporary outage of network, which led to failure in resolving r3.o.lencr.org. The network issue should automatically recover after a while, therefore so long as the system keeps retrying restarting nginx, the issue should have gone.

To let the system restart nginx endlessly, I follow the instructions here, and added the following to section [Service] of /lib/systemd/system/nginx.service:

# In section [Service]
Restart=always
RestartSec=10

Hopefully next time the same issue happens again things would recover seemlessly.