diff --git a/.github/workflows/gradle.yml b/.github/workflows/gradle.yml
index 96faab6..a9024c1 100644
--- a/.github/workflows/gradle.yml
+++ b/.github/workflows/gradle.yml
@@ -8,15 +8,15 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v3
-    - name: Set up JDK 17
+    - name: Set up JDK 21
       uses: actions/setup-java@v3
       with:
-        java-version: 17
+        java-version: 21
         distribution: 'zulu'
     - name: Setup Gradle
       uses: gradle/gradle-build-action@v2
       with:
-        gradle-version: 8.3
+        gradle-version: 8.5
         cache-disabled: true
         dependency-graph: generate-and-submit
     - name: Build with Gradle
diff --git a/README.md b/README.md
index 19d7c49..70e4019 100644
--- a/README.md
+++ b/README.md
@@ -13,8 +13,8 @@ Projects:
 - `theory` - examples from the Distributed Systems Basics section
 
 Requires:
-- Java 17
-- Gradle 8.4
+- Java 21
+- Gradle 8.5
 - Docker (to run some samples)
 
  ![build](https://github.com/real-logic/aeron-cookbook-code/workflows/JavaCI/badge.svg)
diff --git a/aeron-mdc/aeron-mdc-publisher/Dockerfile b/aeron-mdc/aeron-mdc-publisher/Dockerfile
index ec1b193..76dc2f6 100644
--- a/aeron-mdc/aeron-mdc-publisher/Dockerfile
+++ b/aeron-mdc/aeron-mdc-publisher/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/aeron-mdc/aeron-mdc-subscriber/Dockerfile b/aeron-mdc/aeron-mdc-subscriber/Dockerfile
index 5a70821..3be34b4 100644
--- a/aeron-mdc/aeron-mdc-subscriber/Dockerfile
+++ b/aeron-mdc/aeron-mdc-subscriber/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/archive-multi-host/archive-client/Dockerfile b/archive-multi-host/archive-client/Dockerfile
index 581fe5c..32b0d78 100644
--- a/archive-multi-host/archive-client/Dockerfile
+++ b/archive-multi-host/archive-client/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/archive-multi-host/archive-host/Dockerfile b/archive-multi-host/archive-host/Dockerfile
index 9090814..b97a1ed 100644
--- a/archive-multi-host/archive-host/Dockerfile
+++ b/archive-multi-host/archive-host/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/archive-replication/archive-backup/Dockerfile b/archive-replication/archive-backup/Dockerfile
index 1bd34f9..e9acafe 100644
--- a/archive-replication/archive-backup/Dockerfile
+++ b/archive-replication/archive-backup/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/archive-replication/archive-client/Dockerfile b/archive-replication/archive-client/Dockerfile
index 2e3bfb1..7443bfc 100644
--- a/archive-replication/archive-client/Dockerfile
+++ b/archive-replication/archive-client/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/archive-replication/archive-host/Dockerfile b/archive-replication/archive-host/Dockerfile
index ecdd012..cf12ef6 100644
--- a/archive-replication/archive-host/Dockerfile
+++ b/archive-replication/archive-host/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/build.gradle.kts b/build.gradle.kts
index 5e2ab29..330cfba 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -5,7 +5,7 @@ plugins {
 
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(17))
+        languageVersion.set(JavaLanguageVersion.of(21))
         vendor.set(JvmVendorSpec.AZUL)
     }
 }
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 75256fa..e027fbd 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -1,13 +1,13 @@
 [versions]
 junitVersion = "5.10.1"
 junitPlatformVersion = "1.10.1"
-checkstyleVersion = "10.12.4"
+checkstyleVersion = "10.12.5"
 aeronVersion = "1.42.1"
 sbeVersion = "1.29.0"
 agronaVersion = "1.19.2"
 slf4jVersion = "2.0.9"
-logbackVersion = "1.4.11"
-mockitoVersion = "5.7.0"
+logbackVersion = "1.4.14"
+mockitoVersion = "5.8.0"
 jmhVersion = "1.37"
 picocliVersion = "4.7.5"
 jlineVersion = "3.24.1"
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 3fa8f86..1af9e09 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.4-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
diff --git a/gradlew b/gradlew
index 0adc8e1..1aa94a4 100755
--- a/gradlew
+++ b/gradlew
@@ -145,7 +145,7 @@ if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
     case $MAX_FD in #(
       max*)
         # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
-        # shellcheck disable=SC3045
+        # shellcheck disable=SC2039,SC3045
         MAX_FD=$( ulimit -H -n ) ||
             warn "Could not query maximum file descriptor limit"
     esac
@@ -153,7 +153,7 @@ if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
       '' | soft) :;; #(
       *)
         # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
-        # shellcheck disable=SC3045
+        # shellcheck disable=SC2039,SC3045
         ulimit -n "$MAX_FD" ||
             warn "Could not set maximum file descriptor limit to $MAX_FD"
     esac
@@ -202,11 +202,11 @@ fi
 # Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
 DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
 
-# Collect all arguments for the java command;
-#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
-#     shell script including quotes and variable substitutions, so put them in
-#     double quotes to make sure that they get re-expanded; and
-#   * put everything else in single quotes, so that it's not re-expanded.
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
 
 set -- \
         "-Dorg.gradle.appname=$APP_BASE_NAME" \
diff --git a/rfq/admin/Dockerfile b/rfq/admin/Dockerfile
index 006aa46..2fbde0d 100644
--- a/rfq/admin/Dockerfile
+++ b/rfq/admin/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]
diff --git a/rfq/cluster/Dockerfile b/rfq/cluster/Dockerfile
index da73e15..7a7d517 100644
--- a/rfq/cluster/Dockerfile
+++ b/rfq/cluster/Dockerfile
@@ -1,6 +1,6 @@
 ARG REPO_NAME=docker.io/
 ARG IMAGE_NAME=azul/zulu-openjdk-debian
-ARG IMAGE_TAG=17
+ARG IMAGE_TAG=21
 FROM ${REPO_NAME}${IMAGE_NAME}:${IMAGE_TAG}
 
 SHELL [ "/bin/bash", "-o", "pipefail", "-c" ]