The landscape of modern enterprise Java development has shifted decisively toward containerization, with OpenJDK 17 serving as a pivotal Long-Term Support (LTS) release. Deploying Java 17 within Docker environments requires a nuanced understanding of base image selection, runtime environment configuration, and the architectural differences between various distribution builds. Whether utilizing Red Hat's enterprise-grade Universal Base Images, Microsoft's cloud-optimized builds, or lightweight Alpine Linux distributions, the objective remains the same: creating a stable, secure, and performant execution environment for Java applications. This guide provides an exhaustive deep dive into the available OpenJDK 17 images, the technicalities of manual image construction, and the operational requirements for deploying fat-jars and flat classpaths across diverse container orchestrators.

Red Hat OpenJDK 17 and the UBI Ecosystem

Red Hat provides a specialized implementation of OpenJDK 17 designed for enterprise stability and seamless integration with Red Hat OpenShift. This offering is built upon the Red Hat Universal Base Image (UBI), which serves as a foundational layer for containerized applications.

The Red Hat build of OpenJDK 17 is a free and open-source implementation of the Java Platform, Standard Edition (Java SE). By utilizing UBI, Red Hat ensures that the images are OCI-compliant, meaning they adhere to the Open Container Initiative standards, ensuring portability across any compliant container engine such as Docker, Podman, or CRI-O.

The specific image ubi8/openjdk-17 (version 1.23) is engineered as a Source To Image (S2I) platform. S2I is a mechanism that allows developers to provide raw source code which is then injected into a builder image to create a runnable container image. This specific image is optimized for building and running plain Java applications, specifically those packaged as fat-jars (where all dependencies are bundled into a single archive) or those utilizing a flat classpath.

Technical specifications for the ubi8/openjdk-17 image include the following:

The use of a non-root user (User 185) and a specific working directory (/home/jboss) is a critical security measure. Running containers as root is a significant security risk; by enforcing a non-privileged user, Red Hat mitigates the potential for container escape attacks. The exposed ports 8080 and 8443 are standard for Java web applications (HTTP and HTTPS), ensuring that the container is network-ready for deployment in OpenShift or Kubernetes environments.

For those needing to analyze the image internals without executing the container, a specific workflow using Podman and Skopeo is recommended:

• Use skopeo to copy the source image to a local directory.
• Use inspect to examine the image metadata.
• Untar the contents to examine the filesystem layers.

Microsoft Build of OpenJDK 17

Microsoft provides a highly optimized set of container images for its build of OpenJDK, catering to different operating system preferences and cloud deployment scenarios. These images are hosted on the Microsoft Container Registry (MCR).

The primary method for acquiring these images is through the docker pull command:

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

The selection of the tag depends entirely on the required base operating system and the JDK version. For OpenJDK 17, the available options are as follows:

• Azure Linux 3.0: Use the tag 17-azurelinux.
• Ubuntu 22.04: Use the tag 17-ubuntu.
• Azure Linux 3.0 Distroless: Use the tag 17-distroless.

The "distroless" variant is particularly significant for security-conscious environments. Distroless images contain only the application and its runtime dependencies; they do not include shell utilities, package managers, or other binaries that are not required for the application to run. This drastically reduces the attack surface of the container.

Furthermore, Microsoft maintains a legacy of tags for those transitioning from older environments. Tags such as 17-mariner (previously built with Mariner 2.0) now mirror the 17-azurelinux tags following the rebranding and upgrade of the Linux distribution to Azure Linux 3.0.

Manual Construction and the Alpine Linux Challenge

For developers who prefer to build their environment from scratch to understand the underlying mechanics or to minimize image size, Alpine Linux is a common choice. However, constructing an OpenJDK 17 image on Alpine requires careful handling of the C library and the Java Runtime Environment (JRE) pathing.

A simplified approach to installing OpenJDK 17 on Alpine 3.16.0 involves using the apk package manager:

```dockerfile

syntax=docker/dockerfile:1

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

Executing this results in the installation of a specific version, such as openjdk 17.0.3 2022-04-19, running on a 64-Bit Server VM.

For those attempting a more manual installation—downloading binaries directly from java.net—the process becomes significantly more complex. This is often done to gain full control over the JDK version and environment variables. An example of a high-complexity manual build involves the following configuration:

```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"]
RUN echo Build Complete ...
```

Troubleshooting Execution Failures in Alpine

A common failure encountered during the manual installation of OpenJDK on Alpine is the /bin/sh: java: not found error during the RUN phase. This usually occurs despite the binaries being present in the filesystem.

When inspecting the directory /usr/java/jdk-17/bin, one may see the necessary binaries:

• java
• javac
• jshell
• jpackage
• jps
• jstack
• jstat
• keytool

The "not found" error in Alpine is frequently not a result of the file being missing, but rather a mismatch between the binary's requirements (typically glibc) and Alpine's provided C library (musl libc). Since standard OpenJDK binaries are compiled for glibc, they cannot execute on a pure Alpine image without a compatibility layer or by using the Alpine-specific packages provided by apk.

Comparative Analysis of OpenJDK 17 Distribution Images

The choice of image significantly impacts the size, security, and maintainability of the application.

Operational Considerations for Java 17 Containers

When deploying OpenJDK 17, engineers must consider the delivery format of the Java application.

The "fat-jar" approach involves bundling all dependencies into a single JAR file. This simplifies deployment as only one file needs to be copied into the container. The Red Hat UBI images are explicitly designed to support this pattern.

Alternatively, a "flat classpath" approach involves placing all dependency JARs in a directory and referencing them during execution. This is often more efficient for layering in Docker, as the dependencies (which change infrequently) can be placed in a separate layer from the application code (which changes frequently), thereby reducing image push/pull times.

Conclusion

The deployment of OpenJDK 17 in Docker environments is not a one-size-fits-all process. For enterprise environments requiring strict compliance and OpenShift integration, the Red Hat UBI 8 images provide a robust, secure, and OCI-compliant foundation. For cloud-native applications on Azure, Microsoft's offerings, especially the distroless variants, provide the optimal balance of performance and security.

The attempt to build manual images on Alpine Linux reveals the critical importance of understanding the underlying C library (musl vs glibc). The /bin/sh: java: not found error serves as a primary example of how architectural mismatches can lead to catastrophic execution failures during the image build phase. Ultimately, the selection of a container image should be driven by the specific needs of the application: distroless for maximum security, UBI for enterprise support, and Alpine for minimal resource consumption.

Sources

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