DOC-313: Kinesis: add option for a rust based mock (#731)

Co-authored-by: Quetzalli <hola@quetzalliwrites.com>
Co-authored-by: Brian Rinaldi <brian.rinaldi@gmail.com>

Author: 3 people

src/content/docs/aws/configuration/config/configuration.md

@@ -246,7 +246,7 @@ Also see [OpenSearch configuration variables](#opensearch) which are used to man
 | `KINESIS_SHARD_LIMIT` | `100` (default), `Infinity` (to disable) | Integer value , causing the Kinesis API to start throwing exceptions to mimic the default shard limit. |
 | `KINESIS_ON_DEMAND_STREAM_COUNT_LIMIT` | `10` (default), `Infinity` (to disable) | Integer value , causing the Kinesis API to start throwing exceptions to mimic the default on demand stream count limit. |
 | `KINESIS_LATENCY` | `500` (default), `0` (to disable)| Integer value of milliseconds, causing the Kinesis API to delay returning a response in order to mimic latency from a live AWS call. |
-| `KINESIS_MOCK_PROVIDER_ENGINE` | `node` (default) \| `scala` | String value of `node` (default) or `scala` that determines the underlying build of Kinesis Mock. |
+| `KINESIS_MOCK_PROVIDER_ENGINE` | `node` (default) \| `scala` \| `rust` | String value of `node` (default), `scala`, or `rust` that determines the underlying build of Kinesis Mock. See [Performance Tuning](/aws/services/kinesis#performance-tuning) for guidance on choosing an engine. |
 | `KINESIS_MOCK_MAXIMUM_HEAP_SIZE` | `512m` (default) | JVM memory format string that sets the maximum memory size for the Kinesis Mock Scala server, corresponds to the JVM `-Xmx` flag. |
 | `KINESIS_MOCK_INITIAL_HEAP_SIZE` | `256m` (default) | JVM memory format string that sets the initial memory size for the Kinesis Mock Scala server, corresponds to the JVM `-Xms` flag. | 
 

src/content/docs/aws/services/kinesis.mdx

@@ -170,21 +170,44 @@ You can fetch the CloudWatch logs for your Lambda function reading records from
 
 ### Performance Tuning
 
-For high-volume workloads or large payloads, we recommend switching to the Scala engine via the `KINESIS_MOCK_PROVIDER_ENGINE=scala` flag, delivering up to 10x better performance compared to the default Node.js engine.
+By default, Kinesis Mock runs on the Node.js engine (`KINESIS_MOCK_PROVIDER_ENGINE=node`).
+For high-volume workloads, large payloads, or long-running setups, you can switch to a different engine using the `KINESIS_MOCK_PROVIDER_ENGINE` flag.
 
-Additionally, the following parameters can be tuned:
+#### Scala engine
+
+The Scala engine (`KINESIS_MOCK_PROVIDER_ENGINE=scala`) delivers up to 10x better performance compared to the default Node.js engine.
+The following parameters can be tuned for the Scala engine:
 
 - Increase `KINESIS_MOCK_MAXIMUM_HEAP_SIZE` beyond the default `512m` to reduce JVM memory pressure.
 - Increase `KINESIS_MOCK_INITIAL_HEAP_SIZE` beyond the default `256m` to pre-allocate more JVM heap memory.
-- Reduce `KINESIS_LATENCY` artificial response delays from the default `500` milliseconds (or disable entirely with `0`).
-
-Refer to our [Kinesis configuration documentation](https://docs.localstack.cloud/references/configuration/#kinesis) for more details on these parameters.
 
 :::note
 `KINESIS_MOCK_MAXIMUM_HEAP_SIZE` and `KINESIS_MOCK_INITIAL_HEAP_SIZE` are only applicable when using the Scala engine.
-Future versions of LocalStack will likely default to using the `scala` engine over the less-performant `node` version currently in use.
 :::
 
+#### Rust engine
+
+The Rust engine (`KINESIS_MOCK_PROVIDER_ENGINE=rust`), introduced in LocalStack 2026.07, is a LocalStack-native rebuild of Kinesis Mock and is the recommended choice for any demanding or long-lived workload.
+It provides:
+
+- **Native multi-account and multi-region support** from a single binary, regardless of how many accounts you use — this removes the per-account instance overhead described under [Limitations](#limitations).
+- **Faithful enforcement of all AWS API limits**, including per-shard rate ingress/egress limits.
+- **An improved persistence model** that replaces the legacy unbounded in-memory queue, allowing the mock to run under sustained load for long periods without the risk of running out of memory.
+
+:::caution
+This is the first release of the Rust engine and it should be considered experimental for anyone opting in.
+
+Persistence is **not compatible** between the Rust engine and the Node.js or Scala engines, in either direction.
+Any existing Kinesis persistence (including Cloud Pods and state created with the `node` or `scala` engines) will not carry over when you switch to `rust` — and vice versa.
+Switching engines effectively starts from a fresh state.
+:::
+
+#### All engines
+
+Regardless of the selected engine, you can reduce `KINESIS_LATENCY` artificial response delays from the default `500` milliseconds (or disable them entirely with `0`).
+
+Refer to our [Kinesis configuration documentation](https://docs.localstack.cloud/aws/configuration/config/configuration/#kinesis) for more details on these parameters.
+
 ## Resource Browser
 
 The LocalStack Web Application provides a Resource Browser for managing Kinesis Streams & Kafka Clusters.
@@ -209,8 +232,10 @@ The following code snippets and sample applications provide practical examples o
 
 ## Limitations
 
-In multi-account setups, each AWS account launches a separate instance of Kinesis Mock, which is very resource intensive when a large number of AWS accounts are used.
-[This Kinesis Mock issue](https://github.com/etspaceman/kinesis-mock/issues/377) is being used to keep track of this feature.
+When using the default Node.js or the Scala engine, each AWS account launches a separate instance of Kinesis Mock in multi-account setups, which is very resource intensive when a large number of AWS accounts are used.
+[This Kinesis Mock issue](https://github.com/etspaceman/kinesis-mock/issues/377) is being used to keep track of this feature for the upstream engines.
+
+The [Rust engine](#performance-tuning) (`KINESIS_MOCK_PROVIDER_ENGINE=rust`) is not affected by this limitation, as it natively supports any number of accounts and regions from a single binary.
 
 ## API Coverage