Docs: New index page (#460)

# Description

*Please add a description here. This will become the commit message of the merge request later.*



Co-authored-by: Felix Hennig <[email protected]>

Author: Felix Hennig

docs/modules/nifi/images/.$nifi_overview.drawio.svg.bkp

@@ -1,7 +1,92 @@
 = Configuration
 
-include::commandline_args.adoc[]
+== Command Line Parameters
 
-include::partial$env_var_args.adoc[]
+This operator accepts the following command line parameters:
 
-include::partial$config_properties.adoc[]
+=== product-config
+
+*Default value*: `/etc/stackable/nifi-operator/config-spec/properties.yaml`
+
+*Required*: false
+
+*Multiple values:* false
+
+[source]
+----
+stackable-nifi-operator run --product-config /foo/bar/properties.yaml
+----
+
+=== watch-namespace
+
+*Default value*: All namespaces
+
+*Required*: false
+
+*Multiple values:* false
+
+The operator will **only** watch for resources in the provided namespace `test`:
+
+[source]
+----
+stackable-nifi-operator run --watch-namespace test
+----
+
+== Environment variables
+
+This operator accepts the following environment variables:
+
+=== PRODUCT_CONFIG
+
+*Default value*: `/etc/stackable/nifi-operator/config-spec/properties.yaml`
+
+*Required*: false
+
+*Multiple values:* false
+
+[source]
+----
+export PRODUCT_CONFIG=/foo/bar/properties.yaml
+stackable-nifi-operator run
+----
+
+or via docker:
+
+----
+docker run \
+    --name nifi-operator \
+    --network host \
+    --env KUBECONFIG=/home/stackable/.kube/config \
+    --env PRODUCT_CONFIG=/my/product/config.yaml \
+    --mount type=bind,source="$HOME/.kube/config",target="/home/stackable/.kube/config" \
+    docker.stackable.tech/stackable/nifi-operator:latest
+----
+
+=== WATCH_NAMESPACE
+
+*Default value*: All namespaces
+
+*Required*: false
+
+*Multiple values:* false
+
+The operator will **only** watch for resources in the provided namespace `test`:
+
+[source]
+----
+export WATCH_NAMESPACE=test
+stackable-nifi-operator run
+----
+
+or via docker:
+
+[source]
+----
+docker run \
+--name nifi-operator \
+--network host \
+--env KUBECONFIG=/home/stackable/.kube/config \
+--env WATCH_NAMESPACE=test \
+--mount type=bind,source="$HOME/.kube/config",target="/home/stackable/.kube/config" \
+docker.stackable.tech/stackable/nifi-operator:latest
+----

docs/modules/nifi/images/nifi_overview.drawio.svg

@@ -1,8 +1,31 @@
 = Stackable Operator for Apache NiFi
+:description: The Stackable Operator for Apache NiFi is a Kubernetes operator that can manage Apache NiFi clusters. Learn about its features, resources, dependencies and demos, and see the list of supported NiFi versions.
+:keywords: k8s, Kubernetes, Stackable Operator, Apache NiFi, open source, operator, data science, data exploration, big data
 
-This is an operator for Kubernetes that can manage https://nifi.apache.org/[Apache NiFi] clusters.
+This Operator manages https://nifi.apache.org/[Apache NiFi] clusters on Kubernetes.
+Apache NiFi is an open-source data integration tool that provides a web-based interface for designing, monitoring and managing data flows between various systems and devices, using a visual programming approach. It supports a wide range of data sources, formats and features such as data provenance, security and clustering.
 
-WARNING: This operator only works with images from the https://repo.stackable.tech/#browse/browse:docker:v2%2Fstackable%2Fnifi[Stackable] repository
+== Getting started
+
+Get started with Apache NiFi and the Stackable Operator by following the xref:getting_started/index.adoc[] guide. It will guide you through the xref:getting_started/installation.adoc[installation] process and xref:getting_started/first_steps.adoc[connect] to the NiFi web interface. Afterwards have a look at the xref:usage_guide/index.adoc[] to learn how to configure your NiFi instance to your needs or run some <<demos, demos>> to learn more about using NiFi with other components.
+
+== Operator Model
+
+The Operator manages the _NifiCluster_ custom resource. NiFi only has a single process that it needs to run, so the NifiCluster has only a single xref:concepts:roles-and-role-groups.adoc[role]: `node`. This role can be divided in multiple role groups.
+
+image::nifi_overview.drawio.svg[A diagram depicting the Kubernetes resources created by the Stackable Operator for Apache NiFi]
+
+For every role group the Operator creates a ConfigMap and StatefulSet which can have multiple replicas (Pods). Every role group is accessible through it's own Service, and there is a Service for the whole Cluster.
+
+== Dependencies
+
+Apache NiFi depends on Apache ZooKeeper which you can run in Kubernetes with the xref:zookeeper:index.adoc[].
+
+== [[demos]]Demos
+
+NiFi is often a good choice as a first step in a data pipeline when it comes to fetching the data in various formats from various sources. The xref:stackablectl::demos/data-lakehouse-iceberg-trino-spark.adoc[] demo uses NiFi to fetch six different datasets in various formats. The data is then ingested into a Kafka topic. Apache Kafka is also xref:kafka:index.adoc[part of the Stackable platform].
+
+The xref:stackablectl::demos/nifi-kafka-druid-earthquake-data.adoc[] and xref:stackablectl::demos/nifi-kafka-druid-water-level-data.adoc[] demo use NiFi in the same way, both demos showcase downloading data from web APIs and ingesting it into Kafka.
 
 == Supported Versions
 

docs/modules/nifi/pages/commandline_args.adoc

@@ -1,3 +1,52 @@
 = Usage guide
 
-This section will help you to use various aspects of the Stackable Operator for Apache NiFi. For a general introduction into the operator follow the xref:getting_started/index.adoc[] guide.
+This section will help you to use various aspects of the Stackable Operator for Apache NiFi. For a general introduction into the operator follow the xref:getting_started/index.adoc[] guide. Below is a general overview of some configuration aspects, have a look at the sub pages for details.
+
+The cluster is configured via a YAML manifest file. This custom resource specifies the amount of replicas for each role group or role specific configuration like resource requests.
+The following listing shows an example configuration:
+
+[source,yaml]
+----
+apiVersion: nifi.stackable.tech/v1alpha1
+kind: NifiCluster
+metadata:
+  name: simple-nifi
+spec:
+  image:
+    productVersion: 1.18.0
+    stackableVersion: "23.4.0"
+  clusterConfig:
+    zookeeperConfigMapName: simple-nifi-znode  # <1>
+    authentication:  # <2>
+      method:
+        SingleUser:
+          adminCredentialsSecret:
+            name: nifi-admin-credentials-simple
+            namespace: default
+      allowAnonymousAccess: true
+    extraVolumes:  # <3>
+      - name: nifi-client-certs
+        secret:
+          secretName: nifi-client-certs
+    sensitiveProperties:
+      keySecret: nifi-sensitive-property-key
+      autoGenerate: true
+  nodes:
+  roleGroups:
+    default:
+      config:
+        resources:  # <4>
+          cpu:
+            min: "500m"
+            max: "4"
+          memory:
+            limit: '2Gi'
+        replicas: 3
+----
+
+<1>: The xref:usage_guide/zookeeper-connection.adoc[ZooKeeper instance] to use.
+<2>: How users should xref:usage_guide/security.adoc[authenticate] themselves.
+<3>: xref:usage_guide/extra-volumes.adoc[Extra volumes] with files that can be referenced in custom workflows.
+<4>: xref:usage_guide/resource-configuration.adoc[CPU and memory configuration] can be set per role group.
+
+Not shown are the common settings for xref:usage_guide/cluster-operations.adoc[starting and stopping the cluster] and xref:usage_guide/pod-placement.adoc[distributing Pods]. Additionally you can set any NiFi setting using xref:usage_guide/configuration-environment-overrides.adoc[overrides]. You can also configure xref:usage_guide/log-aggregation.adoc[log aggregation].

docs/modules/nifi/pages/configuration.adoc

@@ -4,11 +4,13 @@
 
 Every user has to authenticate themselves before using NiFI.
 There are multiple options to set up the authentication of users.
+All authentication related parameters are configured under `spec.clusterConfig.authentication`.
 
 === Single user
 
-The default setting is to only provision a single user with administrative privileges.
-You need to specify the username and password of the user.
+Currently, the only supported authentication method is "SingleUser", which allows the definition of one admin user which can then access the cluster.
+Specification of these users credentials happens via referring to a Secret in Kubernetes, this secret will need to contain at least the two keys `username` and `password`.
+Extra keys may be present, but will be ignored by the operator.
 
 [source,yaml]
 ----
@@ -36,6 +38,11 @@ spec:
 
 Additional users can not be added.
 
+==== Anonymous Access
+
+NiFi can be configured to allow anonymous access to the web UI, this is turned off by default, but can be enabled via the parameter `allowAnonymousAccess`.
+This setting is independent of the configured authentication method and will override anything specified for the authentication provider.
+
 [#authentication-ldap]
 === LDAP
 

docs/modules/nifi/pages/dependencies.adoc

@@ -0,0 +1,12 @@
+= Connecting NiFi to ZooKeeper
+
+NiFi in cluster mode requires a ZooKeeper ensemble for state management and leader election purposes, this operator at the moment does not support single node deployments without ZooKeeper, hence this is a required setting.
+
+[source,yaml]
+----
+spec:
+  clusterConfig:
+    zookeeperConfigMapName: simple-nifi-znode
+----
+
+Configuration happens via a ConfigMap, which needs to contain two keys called `ZOOKEEPER_HOSTS` with the value being the ZooKeeper connection string and `ZOOKEEPER_CHROOT` with the value being the ZooKeeper chroot. This ConfigMap typically is created by a ZookeeperZnode of the xref:zookeeper:index.adoc[ZooKeeper Operator].