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diff --git a/doc/05-Distributed-Setups.md b/doc/05-Distributed-Setups.md new file mode 100644 index 0000000..a324a65 --- /dev/null +++ b/doc/05-Distributed-Setups.md @@ -0,0 +1,85 @@ +# Distributed Setups + +## High Availability + +High availability functionality is built directly into Icinga DB and +can be deployed without additional third-party components. + + + +First, you need an Icinga 2 high availability setup with two master nodes, such as described +[here](https://icinga.com/docs/icinga-2/latest/doc/06-distributed-monitoring#high-availability-master-with-agents). + +Each of the master nodes must have the Icinga DB feature enabled and +have their own dedicated Redis server set up for it, so that each node writes the monitoring data separately. +The setup steps per node are no different from a single node setup and can be found in the +[Icinga 2 installation documentation](https://icinga.com/docs/icinga-2/latest/doc/02-installation). +Each Redis server will always have the complete data available as long as +its corresponding Icinga 2 master is running and writing to its Redis. +This is because the Icinga 2 master nodes synchronize their data and events with each other as long as +they are connected, +and each takes over the entire configuration in case the other node or their connection to each other fails. + +For each Redis server you need to set up its own dedicated Icinga DB instance that connects to it, +but the Icinga DB instances must write to the same database, which of course can be replicated or a cluster. +So the steps from the standard +[Icinga DB installation documentation](https://icinga.com/docs/icinga-db/latest/doc/02-installation) +can be followed. However, as mentioned, the database only needs to be set up once. + +All in all, an Icinga DB HA environment involves setting up two Icinga 2 master nodes, two Redis servers, +two Icinga DB instances and one database. + +Please read the note about the [environment ID](#environment-id), +which is common to all Icinga DB components and generated by Icinga 2's Icinga DB feature. + +There is only one Icinga DB instance at a time, +which is responsible for performing database operations in the following areas: + +* Synchronizing configuration, also across Icinga 2 restarts. +* Performing configuration runtime updates made via the Icinga 2 API. +* Updating recent host and service states. +* Flagging hosts and services that are overdue for updates. +* Deleting history items that have exceeded their configured retention time. + +However, both Icinga DB instances write all events relevant to the history of hosts and services to the database. +This way, no data is lost if one of the Icinga 2 masters is unavailable or if their connection to each other fails. + +Which Icinga DB instance is responsible is determined by a specific database operation that +can only be performed by one instance first. +In the case of concurrent operations, simply put, only one wins via a locking mechanism. +Of course, this is only true if the environment is healthy. +Icinga DB is not trying to be responsible if its corresponding Redis server is unavailable or +Icinga 2 is not writing data to Redis. +If Icinga 2 or Redis become unavailable for more than 60 seconds, +Icinga DB releases responsibility so the other instance can take over. + +## Multiple Environments + +Icinga DB supports synchronization of monitoring data from multiple different Icinga environments into +a single database. This allows Icinga DB Web to provide a centralized view of the data. +Although everything is prepared in Icinga DB, there is no full support in Icinga DB Web yet. +As soon as it is ready, the documentation will be adapted and the feature will be explained in more detail. + + + +## Environment ID + +!!! important + + Icinga 2 generates a unique environment ID from its CA certificate when it is first started with the + Icinga DB feature enabled. The ID is used in all Icinga DB components to separate data from + multiple different environments and is written to the file `/var/lib/icinga2/icingadb.env` by Icinga 2. + + It is strictly recommended not to change this ID afterwards, as all data would be resynchronized and + the old ones would remain in the database, resulting in duplicate data. As long as the file remains, + Icinga 2 will not regenerate the environment ID. This is also true if the CA is changed to avoid duplicate data. + Special care should be taken if you add or redeploy the master node(s) and + as a result or over time the CA has changed, which would result in a new environment ID. + If this is the case, make sure you copy the file between your Icinga 2 masters to get a consistent ID. + + For high-availability setups, it is a good idea to enable the Icinga DB feature on the secondary master after + you have successfully connected from/to the primary master so that the certificates are set up properly. + The secondary master will then generate the same environment ID since it is working with the same CA certificate. + + In any case make sure that the file `/var/lib/icinga2/icingadb.env` does not change over time and + is the same on all Icinga 2 master nodes per environment. |