LHO-Distributed-NDS-Install.md

@@ -22,6 +22,55 @@ Additional systems required to run
 
 ## Data Flow ##
 
+The data path for the low latency CDS data stream from CDS.
+
 ![Rough_data_flow_of_low_latency_data_in_CDS.svg](uploads/b79839a1634cc5cff23e6cc6e38b4ca0/Rough_data_flow_of_low_latency_data_in_CDS.svg)
 
+The data path from h1daqgds1 to a nds node in LDAS.
+
 ![Rough_data_flow_of_low_latency_data_to_NDS.svg](uploads/ed2e3a81eec8d8ca48a51b6e2dc35826/Rough_data_flow_of_low_latency_data_to_NDS.svg)
+
+## Services ##
+
+The nodes in the NDS cluster run a number of services.
+
+### HA-Proxy ###
+
+
+| item | description |
+| ------ | ------ |
+| systemd unit| nds-proxy |
+| role | load balancing proxy that distributes requests through all the worker nodes.  Allows unauthenticated connections or GSSAPI authenticated connections |
+| config dir | /etc/ndsproxy |
+| number in cluster | 1 |
+
+Other notes.
+
+The proxy can act in a few roles:
+
+ 1. a load balancing proxy
+ 1. a simple metric collector
+ 1. a central configuration point.
+    * each of the io-nodes are set up to pull their configuration from the proxy.
+
+| Interface | purpose |
+| ------ | ------ |
+| nds2a.ligo-wa.caltech.edu:31200 | the public authenticated nds2 interface |
+| nds-1.dcs:31200 | the internal unauthenticated nds2 interface |
+| nds-1.dcs:31205 | the internal r/o admin reporting interface (simple stats reporting, and config) |
+| nds-1.dcs:31206 | simple stats collection (for the nds2 io nodes ) |
+
+
+### NDS Metadata Server ###
+
+| item | description |
+| ------ | ------ |
+| systemd unit | nds-metadata-server |
+| role | This service manages the list of channels, which frames contain them, and when |
+| channel list directory | /var/lib/ndsmetadata |
+
+Notes:
+
+This service can be restarted as needed.  Restarting willonly interrupt current metadata requests, not data requests.
+
+Requires the diskcache server to be running.