extend admin docs on UI

docs/administrator.md

@@ -486,29 +486,36 @@ A secret can be pre-provisioned in different ways:
 
 ## Setting up the Postgres Operator UI
 
-With the v1.2 release the Postgres Operator is shipped with a browser-based
+Since the v1.2 release the Postgres Operator is shipped with a browser-based
 configuration user interface (UI) that simplifies managing Postgres clusters
-with the operator. It talks to the K8s API Server as well as the Postgres
-Operator [REST API](developer.md#debugging-the-operator). URLs as well as parts
-of the UI layout can be configured via environment variables in the
-[deployment manifest](../ui/manifests/deployment.yaml#L40).
+with the operator.
 
-The UI runs with Node.js and comes with it's own Docker image. Run NPM to
-continuously compile `tags/js` code. Basically, it creates an `app.js` file in:
-`static/build/app.js`
+### Building the UI image
 
-```bash
-(cd ui/app && npm start)
-```
-
-To build operator UI and Docker image open a shell, change to the `ui` folder
-and run:
+The UI runs with Node.js and comes with it's own Docker
+image. However, installing Node.js to build the operator UI is not required. It
+is handled via Docker containers when running:
 
 ```bash
 make docker
 ```
 
-Apply all manifests from the `ui/manifests` folder to deploy the Postgres
+### Configure endpoints and options
+
+The UI talks to the K8s API server as well as the Postgres Operator [REST API](developer.md#debugging-the-operator).
+K8s API server URLs are loaded from the machine's kubeconfig environment by
+default. Alternatively, a list can also be passed when starting the Python
+application with the `--cluster` option.
+
+The Operator API endpoint can be configured via the `OPERATOR_API_URL`
+environment variables in the [deployment manifest](../ui/manifests/deployment.yaml#L40).
+You can also expose the operator API through a [service](../manifests/api-service.yaml).
+Some displayed options can be disabled from UI using simple flags under the
+`OPERATOR_UI_CONFIG` field in the deployment.
+
+### Deploy the UI on K8s
+
+Now, apply all manifests from the `ui/manifests` folder to deploy the Postgres
 Operator UI on K8s. Replace the image tag in the deployment manifest if you
 want to test the image you've built with `make docker`. Make sure the pods for
 the operator and the UI are both running.
@@ -518,11 +525,17 @@ sed -e "s/\(image\:.*\:\).*$/\1$TAG/" manifests/deployment.yaml | kubectl apply
 kubectl get all -l application=postgres-operator-ui
 ```
 
-For local testing you need to apply proxying and port forwarding so that the UI
-can talk to the K8s and Postgres Operator REST API. The Ingress resource is not
-needed. You can use the provided `run_local.sh` script for this. Make sure
-Python dependencies are installed on your machine and the correct K8s API server
-URL is used, e.g. for minikube it would usually be `https://192.168.99.100:8443`.
+### Local testing
+
+For local testing you need to apply K8s proxying and operator pod port
+forwarding so that the UI can talk to the K8s and Postgres Operator REST API.
+The Ingress resource is not needed. You can use the provided `run_local.sh`
+script for this. Make sure that:
+
+* Python dependencies are installed on your machine
+* the K8s API server URL is set for kubectl commands, e.g. for minikube it would usually be `https://192.168.99.100:8443`.
+* the pod label selectors for port forwarding are correct
+
 When testing with minikube you have to build the image in its docker environment
 (running `make docker` doesn't do it for you). From the `ui` directory execute:
 
@@ -537,7 +550,7 @@ docker build -t registry.opensource.zalan.do/acid/postgres-operator-ui:v1.3.0 .
 # apply UI manifests next to a running Postgres Operator
 kubectl apply -f manifests/
 
-# install python dependencies and run UI locally
+# install python dependencies to run UI locally
 pip3 install -r requirements
 ./run_local.sh
 ```