[Definition]
failregex = .* from ip <HOST>

[express-js]
enabled  = true
filter   = expressjs
logpath  = /var/log/expressjs/slowin-killer.log
maxretry = 5
bantime  = 3600
findtime = 600

[20-5-2017 20:49:57] Failed to authentificate user "dinath.contact@gmail.comdddd" from ip 127.0.0.1
[20-5-2017 20:57:19] Failed to authentificate user "dinath.contact@gmail.comdddd" from ip 127.0.0.1
[20-5-2017 20:59:20] Failed to authentificate user "dinath.contact@gmail.comdddd" from ip 127.0.0.1
[20-5-2017 21:12:47] Failed to authentificate user "dinath.contact@gmail.comdddd" from ip 127.0.0.1
[20-5-2017 21:16:9] Failed to authentificate user "dinath.contact@gmail.comdddd" from ip 127.0.0.1

$ fail2ban-client status expressjs
Status for the jail: expressjs
|- Filter
|  |- Currently failed: 0
|  |- Total failed: 0
|  `- File list:    /var/log/expressjs/slowin-killer.log
`- Actions
   |- Currently banned: 0
   |- Total banned: 0
   `- Banned IP list:

Running tests
=============

Use   failregex filter file : expressjs, basedir: /etc/fail2ban
Use         log file : /var/log/expressjs/slowin-killer.log
Use         encoding : UTF-8


Results
=======

Failregex: 27 total
|-  #) [# of hits] regular expression
|   1) [27] .* from ip <HOST>
`-

Ignoreregex: 0 total

Date template hits:
|- [# of hits] date format
|  [34] Day(?P<_sep>[-/])Month(?P=_sep)(?:Year|Year2) 24hour:Minute:Second
|  [1] (?:DAY )?MON Day Year 24hour:Minute:Second(?:.Microseconds)?
`-

Lines: 162 lines, 0 ignored, 27 matched, 135 missed
[processed in 0.01 sec]

Missed line(s): too many to print.  Use --print-all-missed to print all 135 lines

findtime
          time interval (in seconds) before the current time where failures will count towards a ban.

   maxretry
          number of failures that have to occur in the last findtime seconds to ban then IP.