Added required external components (#461)

* Added required external components

* added to nav and index

* some changes to the getting started guide

docs/modules/druid/pages/getting_started/first_steps.adoc

@@ -61,6 +61,8 @@ include::example$getting_started/getting_started.sh[tag=install-druid]
 
 This will create the actual druid instance.
 
+WARNING: This Druid instance uses Derby (`dbType: derby`) as a metadata store, which is an interal SQL database. It is not persisted and not suitable for production use! Consult the https://druid.apache.org/docs/latest/dependencies/metadata-storage.html#available-metadata-stores[Druid documentation] for a list of supported databases and setup instructions for production instances.
+
 == Verify that it works
 
 Next you will submit an ingestion job and then query the ingested data  - either through the web interface or the API.
@@ -160,8 +162,8 @@ include::example$getting_started/expected_query_result.json[]
 
 image::getting_started/query.png[]
 
-Great! You've set up your first Druid cluster, ingested some data and queried it in the web interface!
+Great! You've set up your first Druid cluster, ingested some data and queried it in the web interface.
 
 == What's next
 
-Have a look at the xref:usage-guide/index.adoc[] page to find out more about the features of the Operator, such as S3-backed deep storage or OPA-based authorization.
+Have a look at the xref:usage-guide/index.adoc[] page to find out more about the features of the Operator, such as S3-backed deep storage (as opposed to the HDFS backend used in this guide) or OPA-based authorization.

docs/modules/druid/pages/index.adoc

@@ -34,7 +34,11 @@ The Druid Operator has the following dependencies:
 * The xref:commons-operator:index.adoc[] provides common CRDs such as xref:concepts:s3.adoc[] CRDs.
 * The xref:secret-operator:index.adoc[] is required for things like S3 access credentials or LDAP integration.
 
-Have a look at the xref:getting_started/index.adoc[getting started guide] for an example of a minimal working setup. Druid works well with other Stackable supported products, such as xref:kafka:index.adoc[Apache Kafka] for data ingestion xref:trino:index.adoc[Trino] for data processing or xref:superset:index.adoc[Superset] for data visualization. xref:opa:index.adoc[OPA] can be connected to create authorization policies. Have a look at the xref:usage-guide/index.adoc[] for more configuration options and have a look at the <<demos, demos>> for complete data pipelines you can install with a single command.
+Have a look at the xref:getting_started/index.adoc[getting started guide] for an example of a minimal working setup.
+
+The getting started guide sets up a fully working Druid cluster, but the S3 deep storage backend as well as the metadata SQL database are xref:required-external-components.adoc[required external components] and need to be set up by you as prerequisites for a production setup.
+
+Druid works well with other Stackable supported products, such as xref:kafka:index.adoc[Apache Kafka] for data ingestion xref:trino:index.adoc[Trino] for data processing or xref:superset:index.adoc[Superset] for data visualization. xref:opa:index.adoc[OPA] can be connected to create authorization policies. Have a look at the xref:usage-guide/index.adoc[] for more configuration options and have a look at the <<demos, demos>> for complete data pipelines you can install with a single command.
 
 == [[demos]]Demos
 

docs/modules/druid/pages/required-external-components.adoc

@@ -0,0 +1,9 @@
+# Required external components
+
+Druid uses an SQL database to store metadata. Consult the https://druid.apache.org/docs/latest/dependencies/metadata-storage.html#available-metadata-stores[Druid documentation] for a list of supported databases and setup instructions.
+
+## Feature specific: S3 and cloud deep storage
+
+https://druid.apache.org/docs/latest/dependencies/deep-storage.html[Deep storage] is where segments are stored. Druid offers multiple storage backends. For the local storage there are no prerequisites. HDFS deep storage can be set up with the xref:hdfs:index.adoc[Stackable Operator for Apache HDFS]. For S3 deep storage or the Google Cloud and Azure storage backends, you need to set up the storage.
+
+Read the xref:usage-guide/deep-storage.adoc[deep storage usage guide] to learn more about configuring Druid deep storage.

docs/modules/druid/pages/usage-guide/deep-storage.adoc

@@ -1,8 +1,10 @@
 = Deep storage configuration
 
+https://druid.apache.org/docs/latest/dependencies/deep-storage.html[Deep Storage] is where Druid stores data segments. For a Kubernetes environment, either the HDFS or S3 backend is recommended.
+
 == [[hdfs]]HDFS
 
-Druid can use HDFS as a backend for deep storage:
+Druid can use HDFS as a backend for deep storage, which requires having an HDFS instance running. You can use the xref:hdfs:index.adoc[Stackable Operator for Apache HDFS] to run HDFS. Configure the HDFS deep storage backend in your Druid cluster this way:
 
 [source,yaml]
 ----
@@ -80,4 +82,4 @@ include::partial$s3-note.adoc[]
 
 === S3 Credentials
 
-include::partial$s3-credentials.adoc[]
+include::partial$s3-credentials.adoc[]

docs/modules/druid/partials/nav.adoc

@@ -12,5 +12,6 @@
 ** xref:druid:usage-guide/monitoring.adoc[]
 ** xref:druid:usage-guide/configuration-and-environment-overrides.adoc[]
 ** xref:druid:usage-guide/cluster_operations.adoc[]
+* xref:druid:required-external-components.adoc[]
 * xref:druid:configuration.adoc[]