[website] Move Concepts and Architecture page into a seperate categ…

…ory (apache#2276)

### Changes

Break down the `Concepts and Architecture` page into multiple pages and move it as a separate top-level category.

site2/docs/admin-api-clusters.md

@@ -49,7 +49,7 @@ admin.clusters().createCluster(clusterName, clusterData);
 
 ### Initialize cluster metadata
 
-When provision a new cluster, you need to initialize that cluster's [metadata](getting-started-concepts-and-architecture.md#metadata-store). When initializing cluster metadata, you need to specify all of the following:
+When provision a new cluster, you need to initialize that cluster's [metadata](concepts-architecture-overview.md#metadata-store). When initializing cluster metadata, you need to specify all of the following:
 
 * The name of the cluster
 * The local ZooKeeper connection string for the cluster

site2/docs/administration-proxy.md

@@ -4,7 +4,7 @@ title: The Pulsar proxy
 sidebar_label: Pulsar proxy
 ---
 
-The [Pulsar proxy](getting-started-concepts-and-architecture.md#pulsar-proxy) is an optional gateway that you can run over the brokers in a Pulsar cluster. We recommend running a Pulsar proxy in cases when direction connections between clients and Pulsar brokers are either infeasible, undesirable, or both, for example when running Pulsar in a cloud environment or on [Kubernetes](https://kubernetes.io) or an analogous platform.
+The [Pulsar proxy](concepts-architecture-overview.md#pulsar-proxy) is an optional gateway that you can run over the brokers in a Pulsar cluster. We recommend running a Pulsar proxy in cases when direction connections between clients and Pulsar brokers are either infeasible, undesirable, or both, for example when running Pulsar in a cloud environment or on [Kubernetes](https://kubernetes.io) or an analogous platform.
 
 ## Running the proxy
 

site2/docs/administration-zk-bk.md

@@ -7,7 +7,7 @@ sidebar_label: ZooKeeper and BookKeeper
 Pulsar relies on two external systems for essential tasks:
 
 * [ZooKeeper](https://zookeeper.apache.org/) is responsible for a wide variety of configuration- and coordination-related tasks.
-* [BookKeeper](http://bookkeeper.apache.org/) is responsible for [persistent storage](getting-started-concepts-and-architecture.md#persistent-storage) of message data.
+* [BookKeeper](http://bookkeeper.apache.org/) is responsible for [persistent storage](concepts-architecture-overview.md#persistent-storage) of message data.
 
 ZooKeeper and BookKeeper are both open-source [Apache](https://www.apache.org/) projects.
 
@@ -171,7 +171,7 @@ BookKeeper is responsible for all durable message storage in Pulsar. BookKeeper
 
 ### Deploying BookKeeper
 
-BookKeeper provides [persistent message storage](getting-started-concepts-and-architecture.md#persistent-storage) for Pulsar.
+BookKeeper provides [persistent message storage](concepts-architecture-overview.md#persistent-storage) for Pulsar.
 
 Each Pulsar broker needs to have its own cluster of bookies. The BookKeeper cluster shares a local ZooKeeper quorum with the Pulsar cluster.
 

site2/docs/client-libraries-go.md

@@ -199,7 +199,7 @@ Parameter | Description | Default
 `MaxPendingMessages` | The maximum size of the queue holding pending messages (i.e. messages waiting to receive an acknowledgment from the [broker](reference-terminology.md#broker)). By default, when the queue is full all calls to the `Send` and `SendAsync` methods will fail *unless* `BlockIfQueueFull` is set to `true`. |
 `MaxPendingMessagesAcrossPartitions` | |
 `BlockIfQueueFull` | If set to `true`, the producer's `Send` and `SendAsync` methods will block when the outgoing message queue is full rather than failing and throwing an error (the size of that queue is dictated by the `MaxPendingMessages` parameter); if set to `false` (the default), `Send` and `SendAsync` operations will fail and throw a `ProducerQueueIsFullError` when the queue is full. | `false`
-`MessageRoutingMode` | The message routing logic (for producers on [partitioned topics](getting-started-concepts-and-architecture.md#partitioned-topics)). This logic is applied only when no key is set on messages. The available options are: round robin (`pulsar.RoundRobinDistribution`, the default), publishing all messages to a single partition (`pulsar.UseSinglePartition`), or a custom partitioning scheme (`pulsar.CustomPartition`). | `pulsar.RoundRobinDistribution`
+`MessageRoutingMode` | The message routing logic (for producers on [partitioned topics](concepts-architecture-overview.md#partitioned-topics)). This logic is applied only when no key is set on messages. The available options are: round robin (`pulsar.RoundRobinDistribution`, the default), publishing all messages to a single partition (`pulsar.UseSinglePartition`), or a custom partitioning scheme (`pulsar.CustomPartition`). | `pulsar.RoundRobinDistribution`
 `HashingScheme` | The hashing function that determines the partition on which a particular message is published (partitioned topics only). The available options are: `pulsar.JavaStringHash` (the equivalent of `String.hashCode()` in Java), `pulsar.Murmur3_32Hash` (applies the [Murmur3](https://en.wikipedia.org/wiki/MurmurHash) hashing function), or `pulsar.BoostHash` (applies the hashing function from C++'s [Boost](https://www.boost.org/doc/libs/1_62_0/doc/html/hash.html) library) | `pulsar.JavaStringHash`
 `CompressionType` | The message data compression type used by the producer. The available options are [`LZ4`](https://github.com/lz4/lz4) and [`ZLIB`](https://zlib.net/). | No compression
 `MessageRouter` | By default, Pulsar uses a round-robin routing scheme for [partitioned topics](cookbooks-partitioned.md). The `MessageRouter` parameter enables you to specify custom routing logic via a function that takes the Pulsar message and topic metadata as an argument and returns an integer (where the ), i.e. a function signature of `func(Message, TopicMetadata) int`. |
@@ -252,9 +252,9 @@ Method | Description | Return type
 `Receive(context.Context)` | Receives a single message from the topic. This method blocks until a message is available. | `(Message, error)`
 `Ack(Message)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) a message to the Pulsar [broker](reference-terminology.md#broker) | `error`
 `AckID(MessageID)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) a message to the Pulsar [broker](reference-terminology.md#broker) by message ID | `error`
-`AckCumulative(Message)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) *all* the messages in the stream, up to and including the specified message. The `AckCumulative` method will block until the ack has been sent to the broker. After that, the messages will *not* be redelivered to the consumer. Cumulative acking can only be used with a [shared](getting-started-concepts-and-architecture.md#shared) subscription type.
+`AckCumulative(Message)` | [Acknowledges](reference-terminology.md#acknowledgment-ack) *all* the messages in the stream, up to and including the specified message. The `AckCumulative` method will block until the ack has been sent to the broker. After that, the messages will *not* be redelivered to the consumer. Cumulative acking can only be used with a [shared](concepts-messaging.md#shared) subscription type.
 `Close()` | Closes the consumer, disabling its ability to receive messages from the broker | `error`
-`RedeliverUnackedMessages()` | Redelivers *all* unacknowledged messages on the topic. In [failover](getting-started-concepts-and-architecture.md#failover) mode, this request is ignored if the consumer isn't active on the specified topic; in [shared](getting-started-concepts-and-architecture.md#shared) mode, redelivered messages are distributed across all consumers connected to the topic. **Note**: this is a *non-blocking* operation that doesn't throw an error. |
+`RedeliverUnackedMessages()` | Redelivers *all* unacknowledged messages on the topic. In [failover](concepts-messaging.md#failover) mode, this request is ignored if the consumer isn't active on the specified topic; in [shared](concepts-messaging.md#shared) mode, redelivered messages are distributed across all consumers connected to the topic. **Note**: this is a *non-blocking* operation that doesn't throw an error. |
 
 #### Receive example
 

site2/docs/client-libraries-java.md

@@ -146,7 +146,7 @@ When using partitioned topics, you can specify the routing mode whenever you pub
 
 ### Async send
 
-You can also publish messages [asynchronously](getting-started-concepts-and-architecture.md#send-modes) using the Java client. With async send, the producer will put the message in a blocking queue and return immediately. The client library will then send the message to the broker in the background. If the queue is full (max size configurable), the producer could be blocked or fail immediately when calling the API, depending on arguments passed to the producer.
+You can also publish messages [asynchronously](concepts-messaging.md#send-modes) using the Java client. With async send, the producer will put the message in a blocking queue and return immediately. The client library will then send the message to the broker in the background. If the queue is full (max size configurable), the producer could be blocked or fail immediately when calling the API, depending on arguments passed to the producer.
 
 Here's an example async send operation:
 
@@ -178,7 +178,7 @@ get a future returned.
 
 In Pulsar, consumers subscribe to topics and handle messages that producers publish to those topics. You can instantiate a new [consumer](reference-terminology.md#consumer) by first instantiating a {@inject: javadoc:PulsarClient:/client/org/apache/pulsar/client/api/PulsarClient} object and passing it a URL for a Pulsar broker (as [above](#client-configuration)).
 
-Once you've instantiated a {@inject: javadoc:PulsarClient:/client/org/apache/pulsar/client/api/PulsarClient} object, you can create a {@inject: javadoc:Consumer:/client/org/apache/pulsar/client/api/Consumer} by specifying a [topic](reference-terminology.md#topic) and a [subscription](getting-started-concepts-and-architecture.md#subscription-modes).
+Once you've instantiated a {@inject: javadoc:PulsarClient:/client/org/apache/pulsar/client/api/PulsarClient} object, you can create a {@inject: javadoc:Consumer:/client/org/apache/pulsar/client/api/Consumer} by specifying a [topic](reference-terminology.md#topic) and a [subscription](concepts-messaging.md#subscription-modes).
 
 ```java
 Consumer consumer = client.newConsumer()
@@ -218,7 +218,7 @@ Consumer consumer = client.newConsumer()
 
 ### Async receive
 
-The `receive` method will receive messages synchronously (the consumer process will be blocked until a message is available). You can also use [async receive](getting-started-concepts-and-architecture.md#receive-modes), which will return immediately with a [`CompletableFuture`](http://www.baeldung.com/java-completablefuture) object that completes once a new message is available.
+The `receive` method will receive messages synchronously (the consumer process will be blocked until a message is available). You can also use [async receive](concepts-messaging.md#receive-modes), which will return immediately with a [`CompletableFuture`](http://www.baeldung.com/java-completablefuture) object that completes once a new message is available.
 
 Here's an example:
 
@@ -230,7 +230,7 @@ Async receive operations return a {@inject javadoc:Message:/client/org/apache/pu
 
 ### Multi-topic subscriptions
 
-In addition to subscribing a consumer to a single Pulsar topic, you can also subscribe to multiple topics simultaneously using [multi-topic subscriptions](getting-started-concepts-and-architecture.md#multi-topic-subscriptions). To use multi-topic subscriptions you can supply either a regular expression (regex) or a `List` of topics. If you select topics via regex, all topics must be within the same Pulsar namespace.
+In addition to subscribing a consumer to a single Pulsar topic, you can also subscribe to multiple topics simultaneously using [multi-topic subscriptions](concepts-messaging.md#multi-topic-subscriptions). To use multi-topic subscriptions you can supply either a regular expression (regex) or a `List` of topics. If you select topics via regex, all topics must be within the same Pulsar namespace.
 
 Here are some examples:
 
@@ -302,7 +302,7 @@ consumerBuilder
 
 ## Reader interface {#readers}
 
-With the [reader interface](getting-started-concepts-and-architecture.md#reader-interface), Pulsar clients can "manually position" themselves within a topic, reading all messages from a specified message onward. The Pulsar API for Java enables you to create  {@inject: javadoc:Reader:/client/org/apache/pulsar/client/api/Reader} objects by specifying a topic, a {@inject: javadoc:MessageId:/client/org/apache/pulsar/client/api/MessageId}, and {@inject javadoc:ReaderConfiguration:/client/org/apache/pulsar/client/api/ReaderConfiguration}.
+With the [reader interface](concepts-clients.md#reader-interface), Pulsar clients can "manually position" themselves within a topic, reading all messages from a specified message onward. The Pulsar API for Java enables you to create  {@inject: javadoc:Reader:/client/org/apache/pulsar/client/api/Reader} objects by specifying a topic, a {@inject: javadoc:MessageId:/client/org/apache/pulsar/client/api/MessageId}, and {@inject javadoc:ReaderConfiguration:/client/org/apache/pulsar/client/api/ReaderConfiguration}.
 
 Here's an example:
 
@@ -327,7 +327,7 @@ The code sample above shows pointing the `Reader` object to a specific message (
 
 ## Schemas
 
-In Pulsar, all message data consists of byte arrays "under the hood." [Message schemas](getting-started-concepts-and-architecture.md#schema-registry) enable you to use other types of data when constructing and handling messages (from simple types like strings to more complex, application-specific types). If you construct, say, a [producer](#producers) without specifying a schema, then the producer can only produce messages of type `byte[]`. Here's an example:
+In Pulsar, all message data consists of byte arrays "under the hood." [Message schemas](concepts-schema-registry.md) enable you to use other types of data when constructing and handling messages (from simple types like strings to more complex, application-specific types). If you construct, say, a [producer](#producers) without specifying a schema, then the producer can only produce messages of type `byte[]`. Here's an example:
 
 ```java
 Producer<byte[]> producer = client.newProducer()

site2/docs/client-libraries-python.md

@@ -79,7 +79,7 @@ client.close()
 
 ### Reader interface example
 
-You can use the Pulsar Python API to use the Pulsar [reader interface](getting-started-concepts-and-architecture.md#reader-interface). Here's an example:
+You can use the Pulsar Python API to use the Pulsar [reader interface](concepts-clients.md#reader-interface). Here's an example:
 
 ```python
 # MessageId taken from a previously fetched message