bazel run *_deploy.jar fails with "cannot execute binary file"

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06-10-2024

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"Cannot Execute Binary File": Troubleshooting Bazel's *_deploy.jar Execution Error

Problem: You're trying to run your application's deployment artifact, *_deploy.jar, using bazel run, but encounter the dreaded "cannot execute binary file" error.

Rephrased: Imagine you've built a house (your application) and created a box (the *_deploy.jar) containing everything needed to set it up on a new plot of land (your deployment environment). But when you try to open the box (run the JAR), it says it's broken and can't be used.

Scenario:

Let's say you've built a simple Java application using Bazel and want to deploy it. Your BUILD file looks like this:

java_binary(
    name = "my_app",
    srcs = ["main.java"],
    main_class = "com.example.MyApp",
)

genrule(
    name = "deploy_jar",
    outs = ["my_app_deploy.jar"],
    cmd = "cp $(location my_app) my_app_deploy.jar",
)

You then attempt to run the deployment JAR:

bazel run //:deploy_jar

And receive the infamous error:

ERROR: /path/to/workspace/bazel-bin/my_app_deploy.jar: cannot execute binary file

Analysis:

The "cannot execute binary file" error typically arises due to a mismatch between the binary's architecture (e.g., 32-bit or 64-bit) and the environment you're trying to run it on. Other causes could be:

• Incorrect file permissions: The JAR file may lack the necessary execution permissions.
• Corrupted or incomplete JAR: The deployment process might have failed, resulting in a broken or incomplete JAR.
• Missing dependencies: Essential libraries or runtime components might be missing from your environment.

Troubleshooting:

1. Verify Target Architecture:
   • Ensure the *_deploy.jar was built for the correct architecture (e.g., 64-bit on a 64-bit system). Check your Bazel build environment settings and build targets.
2. Check File Permissions:
   • Run chmod +x /path/to/workspace/bazel-bin/my_app_deploy.jar to grant execution permission to the JAR.
3. Inspect JAR Contents:
   • Use a tool like unzip or a JAR viewer to examine the contents of the *_deploy.jar and verify that all expected files are present.
4. Verify Dependencies:
   • Make sure your deployment environment has the required Java Runtime Environment (JRE) and any other necessary dependencies.

Additional Tips:

• Use a dedicated deployment tool like Docker or a cloud platform like AWS or GCP for a more robust and streamlined deployment process.
• Employ a build automation system (e.g., Jenkins, GitLab CI) to automate your build and deployment pipeline and catch potential errors early.
• Leverage a logging and monitoring system to capture build and deployment events and troubleshoot issues effectively.

References:

• Bazel Documentation
• Docker
• AWS
• GCP

By following these steps and analyzing the error context, you should be able to pinpoint the root cause of the "cannot execute binary file" issue and resolve it effectively. Remember, understanding the error message and taking a systematic approach to troubleshooting are key to resolving build and deployment problems.