Over the last few days the Apache web server that runs on my home server has been acting up again. Every morning I noticed that it had stopped running at some point in the night.
This is not the first time this has happened. In the past, I just restarted the server in the morning and did not think about it too much. After a week or so the issue would typically sort itself out. It's time to fix it properly.
Since the behaviour is intermittent I'm guessing that Apache is crashing, so let's take a look at the error log at /var/log/httpd/error_log. I'm only really interested at events that are happening over night, since that is when the server is crashing. There are ways to filter a log file by a date range, but since the number of lines to go through is small, I didn't think it was worth the effort. Here are the lines of interest for two consecutive days:
[Tue Feb 26 04:20:04.029627 2019] [core:error] [pid 5539:tid 140104264849280] (2)No such file or directory: AH00095: failed to remove PID file /var/run/httpd.pid [Tue Feb 26 04:20:04.076544 2019] [mpm_event:notice] [pid 5539:tid 140104264849280] AH00491: caught SIGTERM, shutting down [Wed Feb 27 04:20:02.324497 2019] [core:error] [pid 11281:tid 140662696130432] (2)No such file or directory: AH00095: failed to remove PID file /var/run/httpd.pid [Wed Feb 27 04:20:02.324674 2019] [mpm_event:notice] [pid 11281:tid 140662696130432] AH00491: caught SIGTERM, shutting down
On both days, Apache receives a SIGTERM signal, it tries (and fails) to delete a PID file and then shuts down. In both cases this happens within seconds of 04:20. This is clearly a shutdown triggered by some external process, rather than a crash. It's also happening at a similar time every night, close to a round number. I suspect that this is caused by some cronjob. Let's take a look:
# Run hourly cron jobs at 47 minutes after the hour: 47 * * * * /usr/bin/run-parts /etc/cron.hourly 1> /dev/null # # Run daily cron jobs at 4:40 every day: 40 4 * * * /usr/bin/run-parts /etc/cron.daily 1> /dev/null # # Run weekly cron jobs at 4:30 on the first day of the week: 30 4 * * 0 /usr/bin/run-parts /etc/cron.weekly 1> /dev/null # # Run monthly cron jobs at 4:20 on the first day of the month: 20 4 1 * * /usr/bin/run-parts /etc/cron.monthly 1> /dev/null # Renew ssl certificates 20 4 * * * /bin/sh -c "/etc/rc.d/rc.httpd stop && letsencrypt renew && /etc/rc.d/rc.httpd start" 1> /dev/null 2>&1
This looks promising, there is a single cronjob running nightly at 04:20 that attempts to renew letsencrypt SSL certificates, and it is shutting down Apache in order to do so. Unfortunately I've been optimistic and redirected all output from that cronjob to /dev/null. Fortunately, letsencrypt is keeping a log of all renewal attempts at /var/log/letsencrypt. Here is the relevant line:
StandaloneBindError: Problem binding to port 80: Could not bind to IPv4 or IPv6.
That's a bit strange. Apache is being stopped before the renewal attempt, so there shouldn't be anything still bound to port 80. I can use netstat to take a look at what is bound to port 80:
# netstat -nlp | grep ':80' | grep -v tcp6
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 11525/nginx: master
I'm using netstat to list listening (-l) ports numericaly (-n), along with the process that owns them (-p). I'm grepping for port 80 and excluding any IPv6 results.
Why is nginx running? I need to have a word with my past self.
Nginx is only listening on port 80 and is configured to always respond with a redirect to https:
worker_processes 1;
events {
worker_connections 1024;
}
http {
include mime.types;
default_type application/octet-stream;
keepalive_timeout 65;
server {
listen 80 default_server;
listen [::]:80 default_server;
server_name _;
return 301 https://$host$request_uri;
}
}
I'm not sure what my thought process was when I set this up. It would be much better to configure Apache to do perform this redirect instead. I'm using Slackware on this server, it doesn't even package nginx so I'm compiling this with a slackbuild from https://slackbuilds.org. Uninstalling it would be desirable.
To perform the same redirect in Apache instead, I've added the following lines to the configuration file (thanks to Gordon on Stackoverflow):
Listen 80
<VirtualHost *:80>
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
</VirtualHost>
This allows Apache to respond to requests on port 80 and adds a default VirtualHost (there are no others for port 80) that responds with a permanent redirect to the https version of the same URL.
The cronjob can now renew the SSL certificates and successfully restart Apache afterwards. For additional robustness, the cronjob should restart Apache whether or not the actual renewal was successful:
# Renew ssl certificates 20 4 * * * /bin/sh -c "/etc/rc.d/rc.httpd stop && letsencrypt renew; /etc/rc.d/rc.httpd start" 1> /dev/null 2>&1
I actually think that I can do one better than that. Certbot has a mature Apache plugin that should be able to handle the renewal process using Apache. I wasn't actually expecting this to work. I changed the value of the authenticator configuration option from standalone to apache in the renewal configuration of letsencrypt. Running certbot renew --dry-run confirms that this works successfully.
I can now make a final change to the cronjob:
# Renew ssl certificates 20 4 * * * certbot renew /dev/null 2>&1