db2_health not working with catalogued databases, as --hostname is always used

[XnS]

Expected Behavior

According to the documentation it is possible to connect to cataloged databases. If that's the case, hostname and port are omitted.
The check command should be rendered to:

check_db2_health --database $db2_health_database$ --report $db2_health_report$ --username $db2_health_username$ --password $db2_health_password$ --mode $db2_health_mode$ --warning $db2_health_warning$ --critical $db2_health_critical$

So that there's no tcp/ip connection involved.

Current Behavior

The --hostname parameter is always used, thus its not possible to connect to cataloged databases as check_db2_health is using tcp/ip mode if --hostname is present.
The rendered check command is:

check_db2_health --hostname $check_address$ --database $db2_health_database$ --report $db2_health_report$ --username $db2_health_username$ --password $db2_health_password$ --mode $db2_health_mode$ --warning $db2_health_warning$ --critical $db2_health_critical$

Possible Solution

It should be possible to specify whether a cataloged database should be used or not. If that's the case, omit --hostname

Steps to Reproduce (for bugs)

1. Create service which uses db2_health command
2. Dont configure a hostname and port
3. Execute check

Context

With the current behaviour no checks of catalogued databases are possible.

Your Environment

• Version used (icinga2 --version):

icinga01:~ # icinga2 --version
icinga2 - The Icinga 2 network monitoring daemon (version: r2.8.4-1)

Copyright (c) 2012-2017 Icinga Development Team (https://www.icinga.com/)
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl2.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Application information:
  Installation root: /usr
  Sysconf directory: /etc
  Run directory: /run
  Local state directory: /var
  Package data directory: /usr/share/icinga2
  State path: /var/lib/icinga2/icinga2.state
  Modified attributes path: /var/lib/icinga2/modified-attributes.conf
  Objects path: /var/cache/icinga2/icinga2.debug
  Vars path: /var/cache/icinga2/icinga2.vars
  PID path: /run/icinga2/icinga2.pid

System information:
  Platform: SLES
  Platform version: 12-SP3
  Kernel: Linux
  Kernel version: 4.4.126-94.22-default
  Architecture: x86_64

Build information:
  Compiler: GNU 4.8.5
  Build host: hostname

• Operating System and version:

icinga01:~ # cat /etc/SuSE-release 
SUSE Linux Enterprise Server 12 (x86_64)
VERSION = 12
PATCHLEVEL = 3
# This file is deprecated and will be removed in a future service pack or release.
# Please check /etc/os-release for details about this release.

• Enabled features (icinga2 feature list):

icinga01:~ # icinga2 feature list
Disabled features: command compatlog debuglog elasticsearch gelf graphite influxdb opentsdb perfdata statusdata syslog
Enabled features: api checker ido-mysql livestatus mainlog notification

• Icinga Web 2 version and modules (System - About):

Icinga Web 2 Version
    2.5.3
Git commit
    ca7e886b820f0145999fdf7377f5c4132301eada
Git commit date
    2018-04-27
Copyright
    © 2013-2018 The Icinga Project 

director master
monitoring 2.5.3
nagvis 1.1.1

• Config validation (icinga2 daemon -C):

icinga01:~ # icinga2 daemon -C
information/cli: Icinga application loader (version: r2.8.4-1)
information/cli: Loading configuration file(s).
information/ConfigItem: Committing config item(s).
information/ApiListener: My API identity: icinga01.company.dmz
warning/ApplyRule: Apply rule 'mail-icingaadmin' (in /etc/icinga2/conf.d/notifications.conf: 11:1-11:45) for type 'Notification' does not match anywhere!
warning/ApplyRule: Apply rule 'mail-icingaadmin' (in /etc/icinga2/conf.d/notifications.conf: 23:1-23:48) for type 'Notification' does not match anywhere!
warning/ApplyRule: Apply rule 'Switch Interface Check' (in /var/lib/icinga2/api/packages/director/icinga01-1527235359-3/zones.d/director-global/service_apply.conf: 1:0-1:75) for type 'Service' does not match anywhere!
information/ConfigItem: Instantiated 1 ApiListener.
information/ConfigItem: Instantiated 3 Zones.
information/ConfigItem: Instantiated 1 Endpoint.
information/ConfigItem: Instantiated 1 FileLogger.
information/ConfigItem: Instantiated 3 ApiUsers.
information/ConfigItem: Instantiated 1 UserGroup.
information/ConfigItem: Instantiated 2 NotificationCommands.
information/ConfigItem: Instantiated 219 CheckCommands.
information/ConfigItem: Instantiated 1 IcingaApplication.
information/ConfigItem: Instantiated 848 Hosts.
information/ConfigItem: Instantiated 24 HostGroups.
information/ConfigItem: Instantiated 1 Downtime.
information/ConfigItem: Instantiated 3 TimePeriods.
information/ConfigItem: Instantiated 1 User.
information/ConfigItem: Instantiated 3 Comments.
information/ConfigItem: Instantiated 22 ServiceGroups.
information/ConfigItem: Instantiated 4977 Services.
information/ConfigItem: Instantiated 1 ScheduledDowntime.
information/ConfigItem: Instantiated 1 CheckerComponent.
information/ConfigItem: Instantiated 1 IdoMysqlConnection.
information/ConfigItem: Instantiated 1 LivestatusListener.
information/ConfigItem: Instantiated 1 NotificationComponent.
information/ScriptGlobal: Dumping variables to file '/var/cache/icinga2/icinga2.vars'
information/cli: Finished validating the configuration file(s).

• If you run multiple Icinga 2 instances, the zones.conf file (or icinga2 object list --type Endpoint and icinga2 object list --type Zone) from all affected nodes.

[dnsmichi]

f0dbcab added a default value into the CheckCommand but it hasn't been documented at all. If we remove it, this likely breaks setups. Not sure where to head here.

[Mikesch-mp]

Lazy as i was, i just copied the text from the plugin. But i will send PR soon, have allready an idea how to do it and not break existing setups. Just have to test it.