Adding upstream version 1.10.2.upstream/1.10.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+<a id="How-it-works"></a>How it works
+=====================================
+
+This chapter wants to give you some basic understanding of how the
+Director works with your Icinga installation. At least once you start
+to work with satellite zones it might be worth to give this a read.
+
+
+How your configuration is going to be rendered
+----------------------------------------------
+
+First of all, the Director doesn't write to `/etc/icinga2`. That's where
+you keep to store your manual configuration and that's where you are
+required to do the basic config tasks required to get Icinga 2 ready for
+the Director.
+
+The Director uses the Icinga 2 API to ship the configuration. It does
+so by shipping full config packages, it does not deal with single
+objects. This makes deployments much faster. It also makes it easier to
+eventually use Director in parallel with manual configuration or
+configuration shipped by other tools.
+
+Internally, Icinga 2 manages part of its configuration in its `var/lib`
+directory. This is usually to be found in `/var/lib/icinga2`. Config
+packages are stored to `/var/lib/icinga2/api/packages` once shipped
+through the API. So as soon as you deployed your first configuration
+with the Director, there will be a new timestamped subdirectory
+containing the new configuration.
+
+Those subdirectories are called stages. You'll often see more than one
+of them. When a new config is deployed, Icinga 2 tries to restart with
+that new stage. In case it fails, Icinga 2 will keep running with the
+former configuration. When it succeeds, it will terminate the old process
+and keep running with the new configuration.
+
+In either scenario, it writes an exit code and its startup log to the
+corresponding stage directory. This allows the Director to check back
+later on to fetch this information. That's why you see all those nice
+startup log outputs along with your deployment history in your frontend.
+
+The configuration in such a stage directory is structured like your
+Icinga 2 config directory in `/etc`: there is a `conf.d` and a `zones.d`
+subdirectory. In `zones.d` Director will create a subdirectory for each
+Zone it wants to deploy config to.
+
+Please note that those `zones.d` subdirectories are subject to config
+sync. To get them syncronized to other nodes, the following must be
+true for them:
+
+* they must have a zone definition for that zone in their local config
+* they must make part of your deployment endpoints zone or be a direct
+  or indirect subzone of that one
+* the `accept_config` setting must be `true` in their `ApiListener`
+  object definition
+
+The director does not try to create additional zones your nodes do not
+know about. In a distributed environment it is essential that the
+Director can ship parts of the configuration to specific zones and
+other parts to a global zone. The name of its preferred global zone
+is currently hardcoded to `director-global`. Please make sure that such
+a zone exists on all involved nodes that should get config from the
+Director in a direct or indirect way:
+
+```icinga2
+object Zone "director-global" {
+  global = true
+}
+```
+
+Please do not use this zone for your own configuration files.
+There is a zone called `global-templates` available in default Icinga
+setups that's meant for configuration files. `director-global` is reserved
+for use by Icinga Director.
+
+Zone membership handling
+------------------------
+
+Mostly you do not need to care much about Zones when working with the
+Director. In case you have no Satellite node, you wouldn't even notice
+their existence.
+
+You are not required to deal with Agent Zones, as the Director does
+this for you. Please refer to [Working with agents](24-Working-with-agents.md)
+for related examples.
+
+Currently the GUI does not allow you to set the zone property on single
+objects. You can circumvent this through the Director's [REST API](70-REST-API.md),
+with Sync rules and through the CLI. However, that shouldn't be part
+of your normal workflow. So if this restriction causes trouble with what
+you want to build please let us know. Explain your scenario, make us
+understand what you want to achieve.
+
+We think of this restriction being a good idea, as it makes things
+easier for most people. That doesn't mean that we would refuse to change
+our mind on this. At least not if you come up with a very good
+reasonable use case.
+
+
+Object rendering
+----------------
+
+This chapter explains where the Director renders which config object to.
+
+* Most objects are rendered to the master zone per default
+* Templates, commands and apply rules are rendered to the global zone
+* Objects with a zone property are rendered to that zone, even if they
+  inherited that property
+* Host objects configured as an Agent are rendered to the master zone,
+  as Director configures them as a Command Execution Bridge
+* Agents with a zone property respect that setting
+* Every command is rendered to the global zone per default
+