concept-guide: add node descriptions (#603)

Partially based on SovereignCloudStack/docs#188

Signed-off-by: Christian Berendt <[email protected]>

docs/guides/concept-guide/hardware-bom.md

@@ -5,12 +5,41 @@ sidebar_position: 50
 
 # Hardware Bill of Materials
 
+## Control nodes
+
+A control node is responsible for running all or most of the OpenStack
+services that manage API services and their associated runtimes. These
+nodes are essential for users to interact with the cluster and maintain
+its managed state.
+
+However, control nodes typically do not run user virtual machines. It is
+therefore advisable to replicate the control nodes to ensure high availability
+and fault tolerance. A good starting point for achieving RAFT quorum is to have
+three control nodes.
+
 ## Compute nodes
 
+Compute nodes are dedicated to running users' virtual machines. They do not
+host API services, storage daemons or network routers, other than the basic
+network infrastructure required to connect virtual machines.
+
 ## Storage nodes
 
+A dedicated storage node runs only storage daemons. This can be necessary in larger
+deployments to protect the storage daemons from  ressource starvation through user
+workloads.
+
 ## Network nodes
 
+A dedicated storage node runs only storage daemons. This setup is essential in
+larger deployments to protect the storage daemons from resource starvation
+caused by user workloads.
+
 ## Manager nodes
 
+The manager node, also known as the deploy node or deployment node, is designated
+to manage the deployment process of all services. It is often also utilized to host
+components of the monitoring services. It serves as the operator's entry point into
+the cluster for operations.
+
 ## Switches

docs/guides/concept-guide/index.md

@@ -49,6 +49,7 @@ sidebar_position: 10
 
 ## Hardware Bill of Materials
 
+* [Control nodes](./hardware-bom#control-nodes)
 * [Compute nodes](./hardware-bom#compute-nodes)
 * [Storage nodes](./hardware-bom#storage-nodes)
 * [Network nodes](./hardware-bom#network-nodes)