diff --git a/Dockerfile b/Dockerfile
index 042438a..34da7a9 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,16 +6,16 @@ RUN yum -y update \
     zlib-devel glibc-static libcxx libcxx-devel llvm-toolset-7 zlib-static \
     && rm -rf /var/cache/yum
 
-ENV JDK_FOLDERNAME jdk-17
-ENV JDK_FILENAME openjdk-17_linux-x64_bin.tar.gz
-RUN curl -4 -L https://download.java.net/java/GA/jdk17/0d483333a00540d886896bac774ff48b/35/GPL/${JDK_FILENAME} | tar -xvz
-RUN mv $JDK_FOLDERNAME /usr/lib/jdk17
+ENV JDK_FOLDERNAME jdk-21
+ENV JDK_FILENAME openjdk-21_linux-x64_bin.tar.gz
+RUN curl -4 -L https://download.oracle.com/java/21/latest/jdk-21_linux-x64_bin.tar.gz | tar -xvz
+RUN mv $JDK_FOLDERNAME /usr/lib/jdk21
 RUN yum install -y binutils
 RUN rm -rf $JDK_FOLDERNAME
-ENV PATH="/usr/lib/jdk17/bin:$PATH"
-RUN jlink --add-modules "$(java --list-modules | cut -f1 -d'@' | tr '\n' ',')" --compress 0 --no-man-pages --no-header-files --strip-debug --output /opt/jre17-slim
-RUN find /opt/jre17-slim/lib -name *.so -exec strip -p --strip-unneeded {} \;
+ENV PATH="/usr/lib/jdk21/bin:$PATH"
+RUN jlink --add-modules "$(java --list-modules | cut -f1 -d'@' | tr '\n' ',')" --compress 0 --no-man-pages --no-header-files --strip-debug --output /opt/jre21-slim
+RUN find /opt/jre21-slim/lib -name *.so -exec strip -p --strip-unneeded {} \;
 RUN java -Xshare:dump -version
-RUN rm /opt/jre17-slim/lib/classlist
-RUN cp /usr/lib/jdk17/lib/server/classes.jsa /opt/jre17-slim/lib/server/classes.jsa
-RUN cd /opt/ && zip -r jre-17-slim.zip jre17-slim
\ No newline at end of file
+RUN rm /opt/jre21-slim/lib/classlist
+RUN cp /usr/lib/jdk21/lib/server/classes.jsa /opt/jre21-slim/lib/server/classes.jsa
+RUN cd /opt/ && zip -r jre-21-slim.zip jre21-slim
diff --git a/README.md b/README.md
index 6bc5167..b00ea56 100644
--- a/README.md
+++ b/README.md
@@ -1,28 +1,35 @@
-# AWS Lambda Java 17 Custom Runtime (DEPRECATED)
+# AWS Lambda Java 21 Custom Runtime
 
-This project is no longer required, as [AWS Lambda now supports Java 17](https://aws.amazon.com/blogs/compute/java-17-runtime-now-available-on-aws-lambda/). I've left it here because others might find it's approach useful for other experimentation. 
+An AWS Lambda layer to enable Java 21 support.
 
+## Usage
 
-An AWS Lambda layer to enable Java 17 support
+### In AWS Console
 
-## Usage
+- Download [java21layer.zip](https://github.com/aleph0io/lambda-java21-layer/releases/download/v21.0.0-alpha.0/java21layer.zip)
+- Upload to S3 (required to create a layer from a ZIP file greater than 50MB in size)
+- In Lambda console, create a layer using this ZIP file using the `x86_64` architecture and the `Custom runtime on Amazon Linux 2` runtime
+- In Lambda console, create a function with `Provide your own bootstrap on Amazon Linux 2` and architecture `x86_64`
+- In Lambda function console, add the layer you created, and upload your [Java deployment package](https://docs.aws.amazon.com/lambda/latest/dg/java-package.html)
+- Run
+- (Hopefully) celebrate! 🥳
 
 ### with CDK
 
-- Download [java17layer.zip](https://github.com/msailes/lambda-java17-layer/releases/download/v0.0.1-alpha/java17layer.zip)
-- Create a Lambda layer using Code.fromAsset `java17layer.zip`
+- Download [java21layer.zip](https://github.com/aleph0io/lambda-java21-layer/releases/download/v21.0.0-alpha.0/java21layer.zip)
+- Create a Lambda layer using Code.fromAsset `java21layer.zip`
 - Note you might need to adjust the path for your own project structure
 
 ```java 
-LayerVersion java17layer = new LayerVersion(this, "Java17Layer", LayerVersionProps.builder()
-        .layerVersionName("Java17Layer")
-        .description("Java 17")
+LayerVersion java21layer = new LayerVersion(this, "Java21Layer", LayerVersionProps.builder()
+        .layerVersionName("Java21Layer")
+        .description("Java 21")
         .compatibleRuntimes(Arrays.asList(Runtime.PROVIDED_AL2))
-        .code(Code.fromAsset("java17layer.zip"))
+        .code(Code.fromAsset("java21layer.zip"))
         .build());
 ```
 
-- Create a function using the PROVIDED_AL2 runtime.
+- Create a function using the `PROVIDED_AL2` runtime.
 - Add this layer to your function.
 
 ```java
@@ -34,18 +41,28 @@ Function exampleWithLayer = new Function(this, "ExampleWithLayer", FunctionProps
         .code(Code.fromAsset("../software/ExampleFunction/target/example.jar"))
         .memorySize(512)
         .logRetention(RetentionDays.ONE_WEEK)
-        .layers(singletonList(java17layer))
+        .layers(singletonList(java21layer))
         .build());
 ```
 
 ## Layer Details
 
-### Java 17 
+### Java 21
 
 A custom JRE is created to reduce final file size. Lambda has a 250MB unzipped file size limit.
 
 [Dockerfile](Dockerfile) describes how the JRE is built.
 
+## Known Issues
+
+Obviously, it's early days, and this is a preliminary release. There are a couple of known issues:
+
+1. The layer fails [CDS](https://docs.oracle.com/javase/8/docs/technotes/guides/vm/class-data-sharing.html) (Class Data Sharing) during initialization. This creates some log traffic, and may adversely affect performance.
+2. It is only (lightly) tested
+3. Only x86_64 is supported
+
+I'll be working on these as I have time. PRs welcome!
+
 ### JVM Settings
 
 The following JVM settings are added by default.
@@ -53,7 +70,7 @@ The following JVM settings are added by default.
 ```
 --add-opens java.base/java.util=ALL-UNNAMED 
 -XX:+TieredCompilation -XX:TieredStopAtLevel=1 
--Xshare:on
+-Xshare:auto
 ```
 
 Further suggestions welcomed
@@ -61,9 +78,9 @@ Further suggestions welcomed
 ### Java Class Path
 
 ```
-aws-lambda-java-runtime-interface-client-1.1.0.jar
-aws-lambda-java-core-1.2.1.jar
-aws-lambda-java-serialization-1.0.0.jar
+aws-lambda-java-core-1.2.3.jar
+aws-lambda-java-serialization-1.1.2.jar
+aws-lambda-java-runtime-interface-client-2.4.1.jar
 $LAMBDA_TASK_ROOT
 $LAMBDA_TASK_ROOT/*
 $LAMBDA_TASK_ROOT/lib/*
@@ -77,6 +94,10 @@ $LAMBDA_TASK_ROOT/lib/*
 
 ### Steps
 
-- Run `build-jre.sh` to build the minimal Java 17 runtime
+- Run `build-jre.sh` to build the minimal Java 21 runtime
 - Run `make-layer.sh` to package the runtime, dependencies and bootstrap as a zip
 
+## Acknowledgements
+
+Much credit to [@msailes](https://github.com/msailes), who created the original repo from which this project is forked!
+
diff --git a/bootstrap b/bootstrap
index 102cd38..ee6b53b 100755
--- a/bootstrap
+++ b/bootstrap
@@ -1,3 +1,5 @@
 #!/bin/sh
 
-/opt/jre17-slim/bin/java --add-opens java.base/java.util=ALL-UNNAMED -XX:+TieredCompilation -XX:TieredStopAtLevel=1 -Xshare:on -cp "/opt/aws-lambda-java-runtime-interface-client-1.1.0.jar:/opt/aws-lambda-java-core-1.2.1.jar:/opt/aws-lambda-java-serialization-1.0.0.jar:$LAMBDA_TASK_ROOT:$LAMBDA_TASK_ROOT/*:$LAMBDA_TASK_ROOT/lib/*" com.amazonaws.services.lambda.runtime.api.client.AWSLambda "$_HANDLER"
+# Should we use -Xshare:on? @msailes did originally...
+# -Xlog:cds is important for solving the CDS problem.
+/opt/jre21-slim/bin/java --add-opens java.base/java.util=ALL-UNNAMED -XX:+TieredCompilation -XX:TieredStopAtLevel=1 -Xshare:auto -cp "/opt/aws-lambda-java-runtime-interface-client-2.4.1.jar:/opt/aws-lambda-java-core-1.2.3.jar:/opt/aws-lambda-java-serialization-1.1.2.jar:$LAMBDA_TASK_ROOT:$LAMBDA_TASK_ROOT/*:$LAMBDA_TASK_ROOT/lib/*" com.amazonaws.services.lambda.runtime.api.client.AWSLambda "$_HANDLER"
diff --git a/build-jre.sh b/build-jre.sh
index 4903f31..1d1f87b 100644
--- a/build-jre.sh
+++ b/build-jre.sh
@@ -1,2 +1,2 @@
-docker build --progress=plain -t jre17-al2-slim .
-docker run -v $(pwd)/layer:/tmp -it jre17-al2-slim sh -c "cp /opt/jre-17-slim.zip /tmp"
\ No newline at end of file
+docker build -t jre21-al2-slim .
+docker run -v $(pwd)/layer:/tmp -it jre21-al2-slim sh -c "cp /opt/jre-21-slim.zip /tmp"
diff --git a/make-layer.sh b/make-layer.sh
index 920d81f..99460c9 100755
--- a/make-layer.sh
+++ b/make-layer.sh
@@ -3,8 +3,20 @@
 # -4 IPv4 only
 # -L follow redirect if the server responds with a redirect
 mkdir layer
-curl -4 -L https://repo.maven.apache.org/maven2/com/amazonaws/aws-lambda-java-runtime-interface-client/1.1.0/aws-lambda-java-runtime-interface-client-1.1.0.jar -o layer/aws-lambda-java-runtime-interface-client-1.1.0.jar
-curl -4 -L https://repo.maven.apache.org/maven2/com/amazonaws/aws-lambda-java-core/1.2.1/aws-lambda-java-core-1.2.1.jar -o layer/aws-lambda-java-core-1.2.1.jar
-curl -4 -L https://repo.maven.apache.org/maven2/com/amazonaws/aws-lambda-java-serialization/1.0.0/aws-lambda-java-serialization-1.0.0.jar -o layer/aws-lambda-java-serialization-1.0.0.jar
+curl -4 -L https://repo.maven.apache.org/maven2/com/amazonaws/aws-lambda-java-runtime-interface-client/2.4.1/aws-lambda-java-runtime-interface-client-2.4.1.jar -o layer/aws-lambda-java-runtime-interface-client-2.4.1.jar
+curl -4 -L https://repo.maven.apache.org/maven2/com/amazonaws/aws-lambda-java-core/1.2.3/aws-lambda-java-core-1.2.3.jar -o layer/aws-lambda-java-core-1.2.3.jar
+curl -4 -L https://repo.maven.apache.org/maven2/com/amazonaws/aws-lambda-java-serialization/1.1.2/aws-lambda-java-serialization-1.1.2.jar -o layer/aws-lambda-java-serialization-1.1.2.jar
 
-chmod 755 bootstrap && zip -r java17layer.zip jre17-slim bootstrap layer/aws-lambda-java-runtime-interface-client-1.1.0.jar layer/aws-lambda-java-core-1.2.1.jar layer/aws-lambda-java-serialization-1.0.0.jar
\ No newline at end of file
+chmod 755 bootstrap
+
+cp bootstrap layer
+
+pushd layer
+
+rm -rf jre21-slim
+unzip jre-21-slim.zip
+
+rm -f ../java21layer.zip
+zip -r ../java21layer.zip bootstrap jre21-slim aws-lambda-java-runtime-interface-client-2.4.1.jar aws-lambda-java-core-1.2.3.jar aws-lambda-java-serialization-1.1.2.jar
+
+popd