Add Peer Forwarder to doc website repo

_data-prepper/peer-forwarder.md

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+---
+layout: default
+title: Peer Forwarder
+nav_order: 12
+---
+
+# Peer Forwarder
+
+Peer Forwarder is an HTTP service that performs peer forwarding of an `event` between Data Prepper nodes for aggregation. This HTTP service uses a hash-ring approach to aggregate events and determine which Data Prepper node should handle on a given trace before rerouting it to that node. Currently, Peer Forwarder is supported by the `aggregate`, `service_map_stateful`, and `otel_trace_raw` processors.
+
+Peer Forwarder groups events based on the identification keys provided by the processors. For `service_map_stateful` and `otel_trace_raw`, the identification key is `traceId` by default and cannot be configured. The `aggregate` processor is configured using the `identification_keys` configuration option. From here, you can specify which keys to use for Peer Forwarder. See [Aggregate Processor page](https://github.com/opensearch-project/data-prepper/tree/main/data-prepper-plugins/aggregate-processor#identification_keys) for more information about identification keys.
+
+Peer discovery allows Data Prepper to find other nodes that it will communicate with. Currently, peer discovery is currently provided by a static list, a DNS record lookup, or AWS Cloud Map.  
+
+## Discovery modes
+
+The following sections provide information about discovery modes.
+
+### Static
+
+Static discovery mode allows a Data Prepper node to discover nodes using a list of IP addresses or domain names. See the following YAML file for an example of static discovery mode:
+
+```yaml
+peer_forwarder:4
+  discovery_mode: static
+  static_endpoints: ["data-prepper1", "data-prepper2"]
+```
+
+### DNS lookup
+
+DNS discovery is preferred over static discovery when scaling out a Data Prepper cluster. DNS discovery configures a DNS provider to return a list of Data Prepper hosts when given a single domain name. This list is a [DNS A record](https://www.cloudflare.com/learning/dns/dns-records/dns-a-record/), and a list of IP addresses of a given domain. See the following YAML file example of DNS lookup:
+
+```yaml
+peer_forwarder:
+  discovery_mode: dns
+  domain_name: "data-prepper-cluster.my-domain.net"
+```
+
+### AWS Cloud Map
+
+[AWS Cloud Map](https://docs.aws.amazon.com/cloud-map/latest/dg/what-is-cloud-map.html) provides API-based service discovery as well as DNS-based service discovery.
+
+Peer Forwarder can use the API-based service discovery. To support this, you must have an existing namespace configured for API instance discovery. You can create a new one by following the instructions provided by the [AWS Cloud Map documentation](https://docs.aws.amazon.com/cloud-map/latest/dg/working-with-namespaces.html).
+
+Your Data Prepper configuration needs to include the following:
+* `aws_cloud_map_namespace_name` – Set to your AWS Cloud Map namespace name.
+* `aws_cloud_map_service_name` – Set to the service name within your specified namespace.
+* `aws_region` – Set to the AWS Region where your namespace exists.
+* `discovery_mode` – Set to `aws_cloud_map`.
+
+Your Data Prepper configuration can optionally include the following:
+* `aws_cloud_map_query_parameters` – Key-value pairs are used to filter the results based on the custom attributes attached to an instance. Results include only those instances that match all of the specified key-value pairs.
+
+#### Example configuration
+
+See the following YAML file example of AWS Cloud Map configuration:
+
+```yaml
+peer_forwarder:
+  discovery_mode: aws_cloud_map
+  aws_cloud_map_namespace_name: "my-namespace"
+  aws_cloud_map_service_name: "data-prepper-cluster"
+  aws_cloud_map_query_parameters:
+    instance_type: "r5.xlarge"
+  aws_region: "us-east-1"
+```
+
+### IAM policy with necessary permissions
+
+Data Prepper must also be running with the necessary permissions. The following AWS Identity and Access Management (IAM) policy shows the necessary permissions:
+
+```json
+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Sid": "CloudMapPeerForwarder",
+            "Effect": "Allow",
+            "Action": "servicediscovery:DiscoverInstances",
+            "Resource": "*"
+        }
+    ]
+}
+```
+
+
+## Configuration
+
+The following table provides optional configuration values.
+
+
+| Value | Type | Description |
+| ----  | --- |  ----------- |
+| `port` | Integer | A value between 0 and 65535 represents the port that the Peer Forwarder server is running on. Default value is `4994`. |
+| `request_timeout` | Integer | Represents the request timeout duration in milliseconds for the Peer Forwarder HTTP server. Default value is `10000`. |
+| `server_thread_count` | Integer | Represents the number of threads used by the Peer Forwarder server. Default value is `200`.|
+| `client_thread_count` | Integer | Represents the number of threads used by the Peer Forwarder client. Default value is `200`.|
+| `maxConnectionCount`  | Integer | Represents the maximum number of open connections for the Peer Forwarder server. Default value is `500`. |
+| `discovery_mode` | String | Represents the peer discovery mode to be used. Allowable values are `local_node`, `static`, `dns`, and `aws_cloud_map`. Defaults to `local_node`, which processes events locally. |
+| `static_endpoints` | List | Contains the endpoints of all Data Prepper instances. Required if `discovery_mode` is set to `static`. |
+|  `domain_name` | String | Represents the single domain name to query DNS against. Typically used by creating multiple [DNS A records](https://www.cloudflare.com/learning/dns/dns-records/dns-a-record/) for the same domain. Required if `discovery_mode` is set to `dns`. |
+| `aws_cloud_map_namespace_name`  | String | Represents the AWS Cloud Map namespace when using AWS Cloud Map service discovery. Required if `discovery_mode` is set to `aws_cloud_map`.  |
+| `aws_cloud_map_service_name` | String | Represents the AWS Cloud Map service when using AWS Cloud Map service discovery. Required if `discovery_mode` is set to `aws_cloud_map`. |
+| `aws_cloud_map_query_parameters`  | Map | Key-value pairs used to filter the results based on the custom attributes attached to an instance. Only instances that match all the specified key-value pairs are returned. |
+| `buffer_size` | Integer | Represents the maximum number of unchecked records the buffer accepts (the number of unchecked records equals the number of records written into the buffer plus the number of records that are still processing and not yet checked by the Checkpointing API). Default is `512`. |
+| `batch_size` |  Integer | Representing max number of records the buffer returns on read. Default is `48`. |
+|  `aws_region` |  String | Represents the AWS Region to use `ACM`, `S3` or `AWS Cloud Map` and is required when any of the following conditions are met:<br> - The `use_acm_certificate_for_ssl` setting is `true`. <br> - Either `ssl_certificate_file` or `ssl_key_file` specifies an AWS S3 URI (for example, s3://mybucket/path/to/public.cert).<br> - The `discovery_mode` setting is `aws_cloud_map`. |
+| `drain_timeout`  | Duration | Represents the wait time for the Peer Forwarder to complete processing data before shutdown. |
+
+## SSL configuration
+
+The following SSL configuration table provides optional SSL configuration values and allows you to set up trust manager for the peer forwarding client to connect to other Data Prepper instances.
+
+| Value | Type | Description |
+| ----- | ---- | ----------- |
+| `ssl` | Boolean | Enables TLS/SSL. Default value is `true`. |
+| `ssl_certificate_file`| String | Representings the SSL certificate chain file path or Amazon Simple Storage Service (Amazon S3) path. The following is an example of an Amazon S3 path: `s3://<bucketName>/<path>`. Defaults to the default certificate file,`config/default_certificate.pem`. See [Default Certificates](https://github.com/opensearch-project/data-prepper/tree/main/examples/certificates) for more information about how the certificate is generated. |
+| `ssl_key_file`| String | Represents the SSL key file path or AWS S3 path. S3 path example `s3://<bucketName>/<path>`. Defaults to `config/default_private_key.pem` which is default private key file. Read more about how the private key file is generated at the [Default Certificates](https://github.com/opensearch-project/data-prepper/tree/main/examples/certificates) page. |
+| `ssl_insecure_disable_verification` | Boolean | that disables the verification of the server's TLS certificate chain. Default value is `false`. |
+| `ssl_fingerprint_verification_only` | Boolean | Disables the verification of the server's TLS certificate chain and instead verifies only the certificate fingerprint. Default value is `false`. |
+| `use_acm_certificate_for_ssl` | Boolean | Enables TLS/SSL using the certificate and private key from AWS Certificate Manager (ACM). Default value is `false`. |
+| `acm_certificate_arn`| String | Representings the ACM certificate Amazon Resource Name (ARN). The ACM certificate takes precedence over S3 or the local file system certificate. Required if `use_acm_certificate_for_ssl` is set to `true`. |
+| `acm_private_key_password` | String | Represents the ACM private key password that will be used to decrypt the private key. If it's not provided, a random password will be generated. |
+| `acm_certificate_timeout_millis` | Integer |representing the timeout in milliseconds required for ACM to get certificates. Default value is `120000`. |
+| `aws_region` | String | Represents the AWS Region that uses `ACM`, `S3` or `AWS Cloud Map`. Required if `use_acm_certificate_for_ssl` is set to `true` or `ssl_certificate_file`. Also required when the `ssl_key_file` is set to the `AWS S3` path, or if `discovery_mode` is set to `aws_cloud_map`. |
+
+#### Example configuration
+
+The following YAML file provides an example configuration:
+
+```yaml
+peer_forwarder:
+  ssl: true
+  ssl_certificate_file: "<cert-file-path>"
+  ssl_key_file: "<private-key-file-path>"
+```
+
+## Authentication
+
+`Authentication` is optional and is a `Map` that enables mutual TLS (mTLS). It can either be `mutual_tls` or `unauthenticated`. The default value is `unauthenticated`. The following YAML file provides an exmaple for authentication:
+
+```yaml
+peer_forwarder:
+  authentication:
+    mutual_tls:
+```
+
+## Metrics
+
+Core Peer Forwarder introduces the following custom metrics. All the metrics are prefixed by `core.peerForwarder`.
+
+### Timer
+
+Peer Forwarder's timer capability provides the following information:
+
+- `requestForwardingLatency`: Measures latency of requests forwarded by the Peer Forwarder client.
+- `requestProcessingLatency`: Measures latency of requests processed by the Peer Forwarder server.
+
+### Counter
+
+The following table provides counter metric options.
+
+| Value | Description |
+| ----- | ----------- |
+| `requests`| Measures the total number of forwarded requests. |
+| `requestsFailed`| Measures the total number of failed requests. Applies to requests with HTTP response code other than `200`. |
+| `requestsSuccessful`|  Measures the total number of successful requests. Applies to requests with HTTP response code `200`. |
+| `requestsTooLarge`| Measures the total number of requests that are too large to be written to the Peer Forwarder buffer. Applies to requests with HTTP response code `413`. |
+| `requestTimeouts`| Measures the total number of requests that time out while writing content to the Peer Forwarder buffer. Applies to requests with HTTP response code `408`. |
+| `requestsUnprocessable`| Measures the total number of requests that fail due to an unprocessable entity. Applies to requests with HTTP response code `422`. |
+| `badRequests`| Measures the total number of requests with bad request format. Applies to requests with HTTP response code `400`. |
+| `recordsSuccessfullyForwarded`| Measures the total number of successfully forwarded records. |
+| `recordsFailedForwarding`| Measures the total number of records fail to be forwarded. |
+| `recordsToBeForwarded` | Measures the total number of records to be forwarded. |
+| `recordsToBeProcessedLocally` | Measures the total number of records to be processed locally. |
+| `recordsActuallyProcessedLocally`| Measures the total number of records actually processed locally. This value is the sum of `recordsToBeProcessedLocally` and `recordsFailedForwarding`. |
+| `recordsReceivedFromPeers`| Measures the total number of records received from remote peers. |
+
+### Gauge
+
+`peerEndpoints` Measures the number of dynamically discovered peer Data Prepper endpoints. For `static` mode, the size is fixed.