"Function Not Implemented" Error in Bazel Docker Builds: A Golang Solution
Scenario: You're building a Golang application with Bazel and using Docker to containerize it. During the build process, you encounter a frustrating error: "could not launch process: fork/exec /go/src/my_bin_svc: function not implemented."
This error indicates a problem within your Docker build context, particularly with how Bazel interacts with Docker. It suggests that the Golang binary produced by Bazel is not correctly configured or linked within the Docker environment.
Let's break it down:
-
Bazel: Bazel is a build tool that efficiently manages your project's dependencies and builds. It plays a crucial role in compiling your Go code into an executable binary.
-
Docker: Docker is a platform for building and running containerized applications. It isolates your application and its dependencies, making it portable and scalable.
-
The "Function Not Implemented" Error: This error arises when the Docker runtime, tasked with running your binary, encounters an issue within the container's environment.
Code Example:
# WORKSPACE file
load("@bazel_tools//tools/docker:docker.bzl", "docker_build")
# BUILD file
docker_build(
name = "my_bin_svc",
base = "ubuntu:latest",
target = "//:my_bin_svc",
args = ["--build-arg", "MY_ENV_VAR=my_value"],
)
Analysis:
The root cause of this error often stems from inconsistencies between the Docker build context and the Bazel-generated binary.
- Path mismatches: Ensure the binary path specified in your Dockerfile (or
docker_buildtarget) is correct and aligns with the location of the Bazel-built binary within the Docker image. - Missing dependencies: Docker might be unable to run the binary if it lacks required shared libraries or dependencies. These could be missing from the base image or might need to be explicitly copied into the image during the build process.
- Permissions issues: In rare cases, incorrect file permissions on the binary within the Docker image could lead to this error.
Debugging and Solutions:
-
Verify the binary location: Double-check the target path in your
docker_buildrule. It should accurately reflect the output location of your Bazel build. -
Check the Docker image: If your Docker image is based on a minimal or stripped-down distribution, it might lack essential libraries required by your binary. Consider using a more complete base image, like a standard Linux distribution.
-
Install dependencies: Explicitly install necessary shared libraries in your Dockerfile:
FROM ubuntu:latest RUN apt-get update && apt-get install -y libstdc++6 -
Copy dependencies: If your binary relies on specific libraries not available in the base image, copy them into the Docker image alongside your binary:
FROM ubuntu:latest COPY libmylib.so /usr/lib/ -
Investigate file permissions: Ensure the binary and its required dependencies have appropriate read and execute permissions within the Docker image.
-
Debug with a shell: Run your Docker container with an interactive shell (
docker run -it my_image /bin/bash). Use this shell to investigate the environment and confirm the binary's presence, permissions, and dependencies.
Additional Considerations:
- Bazel's
--stripflag: This flag removes debugging information from the binary, potentially impacting its ability to run. Consider disabling it if you need debugging symbols. - Multi-stage builds: Employ multi-stage Docker builds to streamline the build process, optimize image size, and avoid potential dependency conflicts.
- Docker image caching: Leveraging Docker image caching can significantly speed up your builds, especially when using complex base images.
Resources:
- Bazel Docker integration: https://docs.bazel.build/versions/master/rules-docker.html
- Docker documentation: https://docs.docker.com/
Conclusion:
The "function not implemented" error in your Bazel Docker build is a common problem that arises from discrepancies in the Docker environment and the Bazel-generated binary. By meticulously verifying the binary location, checking for missing dependencies, and ensuring proper permissions, you can effectively resolve this error and build your containerized Go application successfully.
