The transition to OpenJDK 17 represents a pivotal shift for Java developers, marking the adoption of a Long-Term Support (LTS) release that introduces significant language enhancements and runtime optimizations. When this powerful runtime is encapsulated within Docker containers, the intersection of Java's memory management and the container's resource isolation creates a complex environment that requires precise configuration. Whether utilizing the Red Hat Universal Base Image, the lightweight Alpine Linux distribution, or the Microsoft Build of OpenJDK, the choice of a base image fundamentally alters the security posture, the image size, and the operational behavior of the application. Containerizing OpenJDK 17 is not merely about wrapping a JAR file; it involves managing the Java Virtual Machine (JVM) flags, ensuring correct classpath resolution for fat-jars, and aligning the base operating system's C-standard library (glibc versus musl) with the JDK's requirements.

Red Hat Universal Base Images (UBI) for OpenJDK 17

Red Hat provides a highly specialized container ecosystem centered around the Universal Base Image (UBI). The ubi8/openjdk-17 image is engineered specifically for enterprise-grade deployments, particularly those targeting Red Hat OpenShift environments.

The Red Hat build of OpenJDK is a free and open source implementation of the Java Platform, Standard Edition (Java SE). By leveraging UBI, Red Hat ensures that the base operating system images are OCI-compliant, meaning they adhere to the Open Container Initiative standards, allowing them to be run across any compatible container engine regardless of the vendor.

Technical Specifications of the Red Hat OpenJDK 17 Image:

The impact of using the ubi8/openjdk-17 image is most evident in the deployment pipeline. Because it contains Source To Image (S2I) integration scripts, it is optimized for OpenShift. This allows the platform to automatically inject source code into the image and build the application without requiring a manual Dockerfile for every microservice. For the developer, this means a faster transition from Git commit to a running pod.

The image is designed as a platform for building and running plain Java applications. It specifically supports two primary deployment patterns:

• fat-jar: A single executable JAR containing all dependencies, which simplifies distribution.
• flat classpath: A directory structure where dependencies are exploded, often used to improve startup time and memory efficiency in certain JVM configurations.

To interact with this image using tools like Podman or Skopeo, a specific workflow is required to inspect the underlying layers. For example, using skopeo to copy the image to a local directory allows an engineer to untar the contents and examine the filesystem layers, ensuring that no unauthorized binaries are present and that the openjdk installation is correctly mapped.

Microsoft Build of OpenJDK Container Strategies

Microsoft provides a diverse array of container images for the Microsoft Build of OpenJDK, catering to different trade-offs between compatibility and image size. These images are hosted on the Microsoft Container Registry (MCR).

The primary command to acquire these images is:

bash docker pull mcr.microsoft.com/openjdk/jdk:<tag>

The selection of the base OS significantly impacts the runtime environment. Microsoft offers several variants for OpenJDK 17:

• Azure Linux 3.0: The modern standard for Microsoft's cloud environment. The tag used is 17-azurelinux.
• Ubuntu 22.04: Provides a familiar ecosystem for developers who rely on Debian-based tooling. The tag used is 17-ubuntu.
• Distroless: These images contain only the application and its runtime dependencies, removing the shell and package managers. This drastically reduces the attack surface. The tag used is 17-distroless.

Historically, Microsoft used the Mariner distribution, with tags such as 17-mariner. However, these have been rebranded and upgraded to Azure Linux 3.0. Consequently, any legacy tags like 17-mariner now mirror the 17-azurelinux tags.

The scientific basis for the Distroless approach is the principle of least privilege. By removing the shell (/bin/sh), an attacker who finds a remote code execution (RCE) vulnerability in the Java application cannot easily execute shell commands to pivot through the network. This creates a robust security layer that is essential for production workloads.

Alpine Linux and OpenJDK 17: The Lightweight Challenge

Using Alpine Linux for OpenJDK 17 is a common choice for developers seeking to minimize image footprints. However, this approach introduces significant technical hurdles due to the difference between glibc (used by most Linux distributions) and musl libc (used by Alpine).

A common failure point occurs when attempting to manually install the JDK via wget into an Alpine image. Consider the following problematic Dockerfile fragment:

```dockerfile

syntax=docker/dockerfile:1

FROM alpine:3.16.0
RUN apk add --no-cache java-cacerts
ENV JAVAHOME=/opt/openjdk-17
ENV PATH=/opt/openjdk-17/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
ENV JAVAVERSION=17-ea+14
RUN set -eux; \
arch="$(apk --print-arch)"; \
case "$arch" in 'x8664') \
downloadUrl='https://download.java.net/java/GA/jdk17.0.2/dfd4a8d0985749f896bed50d7138ee7f/8/GPL/openjdk-17.0.2linux-x64bin.tar.gz'; \
downloadSha256='0022753d0cceecacdd3a795dd4cea2bd7ffdf9dc06e22ffd1be98411742fbb44'; ;; *) echo >&2 "error: unsupported architecture: '$arch'"; exit 1 ;; \
esac; wget -O openjdk.tgz "$downloadUrl"; echo "$downloadSha256 *openjdk.tgz" | sha256sum -c -; mkdir -p "$JAVAHOME"; tar --extract --file openjdk.tgz --directory "$JAVAHOME" --strip-components 1 --no-same-owner ; rm openjdk.tgz*; rm -rf "$JAVAHOME/lib/security/cacerts"; ln -sT /etc/ssl/certs/java/cacerts "$JAVA_HOME/lib/security/cacerts"; \
java -Xshare:dump; fileEncoding="$(echo 'System.out.println(System.getProperty("file.encoding"))' | jshell -s -)"; [ "$fileEncoding" = 'UTF-8' ]; \
rm -rf ~/.java; \
javac --version; \
java --version
CMD ["jshell"]
```

The failure in the above configuration often manifests as:

```text

10 14.64 + java -Xshare:dump

10 14.64 /bin/sh: java: not found

```

This error is deceptive. Even though the files are present in the directory, the binary cannot be executed because it was compiled against glibc, and Alpine uses musl. When the Linux kernel attempts to load the binary, it fails to find the required dynamic linker, resulting in a "not found" error despite the file physically existing on the disk.

To verify this, an inspection of the binary directory might show the following:

text usr/java/jdk-17/bin # ls -ltra total 456 -rwxr-xr-x 1 10668 10668 12392 Dec 7 2021 serialver -rwxr-xr-x 1 10668 10668 12392 Dec 7 2021 rmiregistry -rwxr-xr-x 1 10668 10668 12392 Dec 7 2021 keytool -rwxr-xr-x 1 10668 10668 12392 Dec 7 2021 jstatd -rwxr-xr-x 1 10668 10668 12384 Dec 7 2021 jstat -rwxr-xr-x 1 10668 10668 12424 Dec 7 2021 jstack -rwxr-xr-x 1 10668 10668 12392 Dec 7 2021 jshell -rwxr-xr-x 1 10668 10668 12424 Dec 7 2021 jrunscript -rwxr-xr-x 1 10668 10668 12384 Dec 7 2021 jps -rwxr-xr-x 1 10668 10668 12392 Dec 7 2021 jpackage

The correct and most efficient way to implement OpenJDK 17 on Alpine is to use the official Alpine package manager (apk), which provides a version of the JDK compiled specifically for musl.

Example of a functional Alpine-based Java 17 Dockerfile:

```dockerfile

syntax=docker/dockerfile:1

FROM alpine:3.16.0
RUN apk add --no-cache java-cacerts openjdk17-jdk
```

When this image is run, the versioning is typically:

text openjdk 17.0.3 2022-04-19 OpenJDK Runtime Environment (build 17.0.3+7-alpine-r2) OpenJDK 64-Bit Server VM (build 17.0.3+7-alpine-r2, mixed mode, sharing)

This approach ensures that the JVM is natively compatible with the base OS, avoiding the "file not found" errors associated with manual binary extraction.

Comparison of OpenJDK 17 Distribution Images

The following table provides a comparative analysis of the different image providers discussed:

Troubleshooting and Configuration in Java 17 Containers

When configuring OpenJDK 17, developers often encounter issues with environment variables and pathing. The JAVA_HOME variable must be explicitly set to the directory where the JDK is installed, and the bin directory of that path must be prepended to the PATH variable.

In the failed manual Alpine attempt, the configuration was:

text ENV JAVA_HOME=/opt/openjdk-17 ENV PATH=/opt/openjdk-17/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

While technically correct in terms of pathing, the failure remained at the binary level. This highlights the importance of using distribution-specific binaries.

Furthermore, managing SSL certificates in Java containers requires attention to the cacerts file. In the manual Alpine approach, the user attempted to link the system certificates to the Java security folder:

bash ln -sT /etc/ssl/certs/java/cacerts "$JAVA_HOME/lib/security/cacerts"

This is a critical step because Java does not natively use the Linux system trust store; it uses its own keystore. Without this link or the java-cacerts package, Java applications will fail to establish HTTPS connections to external APIs.

Conclusion

The selection of a Docker image for OpenJDK 17 is a strategic decision that balances security, size, and compatibility. Red Hat's UBI images provide a robust, enterprise-ready foundation with deep integration into OpenShift through S2I. Microsoft's offerings provide a spectrum of choices, from the versatility of Ubuntu to the hardened security of Distroless images. Meanwhile, Alpine Linux offers the smallest possible footprint, provided that the developer uses the apk package manager to avoid the glibc/musl incompatibility trap.

The transition from manual binary installation to managed package installation is the most significant learning curve for those new to containerization. The "java: not found" error in Alpine is a classic example of the abstraction leak between the container's operating system and the binary's requirements. By utilizing the correct tags and base images, engineers can ensure that their Java 17 applications are portable, secure, and performant across any OCI-compliant runtime.

Sources

1. Red Hat Catalog - OpenJDK 17
2. Docker Forums - OpenJDK Java 17 Docker Image
3. Docker Hub - OpenJDK 17-ea-alpine
4. Microsoft Learn - OpenJDK Containers