#!/bin/bash
# -*- bash -*-

: <<=cut

=head1 NAME

nginx error - Munin plugin to monitor nginx error rates (http status codes per minute).


=head1 APPLICABLE SYSTEMS

Any host running nginx, with bash version > 4.0


=head1 CONFIGURATION

This shows the default configuration of this plugin.  You can override
the log file path and the logpattern.
Additionally you may want to adjust 'group' (or 'user') based on the
permissions required for reading the log file.

  [nginx_error]
        group          adm
	env.logpath    /var/log/nginx
	env.logpattern a.*.log

	Nginx must also be configured to log accesses in "combined" log format (default)


=head1 USAGE

Link this plugin to /etc/munin/plugins/ and restart the munin-node.

This plugin also can be used like wildcard-plugin for monitoring particular virtual host log.
E.g.
    ln -s /usr/share/munin/plugins/nginx_error /etc/munin/plugins/nginx_error_mydomaincom
will parse the log file /var/log/nginx/a.mydomaincom.log

You can change 'env.logpattern' using asterisk ('*') to match your logs filenames.

'env.logpattern' is ignored for a non-symlink configuration.


=head1 INTERPRETATION

The plugin shows nginx http "error" status rates by parsing access log.


=head1 MAGIC MARKERS

 #%# family=auto
 #%# capabilities=autoconf


=head1 BUGS

None known.


=head1 VERSION

1.1 - 2018/01/20
      * add 'dirty config' capability support
      * fix shell style issues reported by shellcheck
      * improve readability of symlink configuration code

1.0 - 2017/02/21


=head1 AUTHOR

vovansystems@gmail.com, 2013


=head1 LICENSE

GPLv3

=cut


set -eu


# default environment variable values
logpath=${logpath:-/var/log/nginx}


# derive the name of the log file from a potential symlink-configured virtual host
script_name=$(basename "$0")
plugin_suffix=${script_name#nginx_error}
if [ -n "${plugin_suffix#_}" ]; then
  # a domain was given via symlink configuration: adjust the logpattern
  domain=${plugin_suffix#_}
  # default logpattern for symlink configuration mode
  logpattern=${logpattern:-a.*.log}
  log_filename=${logpattern/\*/$domain}
else
  log_filename='access.log'
fi

log="$logpath/$log_filename"

# declaring an array with http status codes, we are interested in
declare -A http_codes
http_codes[400]='Bad Request'
http_codes[401]='Unauthorized'
http_codes[403]='Forbidden'
http_codes[404]='Not Found'
http_codes[405]='Method Not Allowed'
http_codes[406]='Not Acceptable'
http_codes[408]='Request Timeout'
http_codes[429]='Too Many Requests'
http_codes[499]='Client Connection Terminated'
http_codes[500]='Internal Server Error'
http_codes[502]='Bad Gateway'
http_codes[503]='Service Unavailable'


# parse error counts from log file
do_fetch () {
  local count status_code
  declare -A line_counts
  values="$(awk '{print $9}' "$log" | sort | uniq -c)"
  # Log files may be empty due to logrotation
  if [ -n "$values" ]; then
    while read -r count status_code; do
      line_counts[$status_code]=$count
    done <<< "$values"
  fi

  for status_code in "${!http_codes[@]}"; do
    echo "error${status_code}.value ${line_counts[$status_code]:-0}"
  done
}


do_config () {
  local status_code
  echo "graph_title $(basename "$log") - Nginx errors per minute"
  echo "graph_vlabel pages with http error codes / \${graph_period}"
  echo "graph_category webserver"
  echo "graph_period minute"
  echo "graph_info This graph shows nginx error rate per minute"
  for status_code in "${!http_codes[@]}"; do
    echo "error${status_code}.type DERIVE"
    echo "error${status_code}.min 0"
    echo "error${status_code}.label $status_code ${http_codes[$status_code]}"
  done
}


do_autoconf () {
  echo yes
}


case ${1:-} in
  config)
    do_config
    # support "dirty config" capability
    if [ "${MUNIN_CAP_DIRTYCONFIG:-0}" = "1" ]; then do_fetch; fi
    ;;
  autoconf)
    do_autoconf
    ;;
  '')
    do_fetch
    ;;
esac

exit $?