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Terraform

AWS CodeBuild Source Command Failing: Troubleshooting Guide

By Filip on 11/13/2024

Learn why you might encounter issues running the `source` command in AWS CodeBuild and discover alternative solutions for sourcing shell scripts during your build process.

AWS CodeBuild Source Command Failing: Troubleshooting Guide

Table of Contents

Introduction

AWS CodeBuild provides a convenient way to automate your build process using a buildspec.yml file. However, it's important to understand how CodeBuild handles environment variables within this file. Each command specified in your buildspec.yml runs in its own shell. This means that changes made to the environment in one command, such as setting variables using source, won't be reflected in subsequent commands.

Step-by-Step Guide

AWS CodeBuild executes commands within your buildspec.yml file sequentially. Each command runs in a separate shell, so changes made by one command, like using source to set environment variables, won't persist to the next.

# This won't work as expected
version: 0.2

phases:
  build:
    commands:
      - source ./set_env.sh
      - echo $MY_VAR # MY_VAR won't be defined here

To ensure environment variables persist, you have two options:

  1. Combine commands: Chain commands using && within a single command entry.
version: 0.2

phases:
  build:
    commands:
      - source ./set_env.sh && echo $MY_VAR
  1. Use a script: Place commands that depend on each other within a script file and execute that script.
version: 0.2

phases:
  build:
    commands:
      - chmod +x ./my_script.sh
      - ./my_script.sh

Remember to specify bash as your shell in buildspec.yml if your script relies on Bash-specific syntax.

version: 0.2

env:
  shells:
    - bash

Code Example

This code demonstrates two ways to persist environment variables across commands in AWS CodeBuild buildspec.yml files. The first method uses '&&' to combine commands within a single shell, ensuring variable availability. The second method defines all commands within a separate bash script, which is then executed by the buildspec.yml file. Both examples include instructions for setting up and running the code in an AWS CodeBuild project.

This repository demonstrates two methods to ensure environment variables persist across commands in your AWS CodeBuild buildspec.yml file.

Project Structure

.
├── set_env.sh
├── my_script.sh
└── buildspec.yml

1. Combining Commands with &&

buildspec.yml:

version: 0.2

phases:
  build:
    commands:
      - source ./set_env.sh && echo $MY_VAR

set_env.sh:

#!/bin/bash
export MY_VAR="Hello from set_env.sh!"

This approach executes both source ./set_env.sh and echo $MY_VAR within the same shell, ensuring MY_VAR is available for the echo command.

2. Using a Script

buildspec.yml:

version: 0.2

env:
  shells:
    - bash

phases:
  build:
    commands:
      - chmod +x ./my_script.sh
      - ./my_script.sh

my_script.sh:

#!/bin/bash

source ./set_env.sh
echo $MY_VAR

This method defines all commands within my_script.sh, ensuring they run in the same shell. The buildspec.yml file then executes this script. Note the use of env: shells: - bash to specify Bash as the shell for the build environment.

Running the Examples

  1. Create an AWS CodeBuild project.
  2. Upload the files to your source code repository.
  3. Configure the CodeBuild project to use your repository and the buildspec.yml file.
  4. Start a build.

You can observe the build logs to confirm that the environment variable MY_VAR is successfully set and accessed in both examples.

Additional Notes

  • Understanding Shell Isolation: The key takeaway is that each command in your buildspec.yml operates within its own isolated shell. This is crucial for parallel task execution but can lead to unexpected behavior with environment variables.

  • Why source Alone Doesn't Work: The source command loads environment variables from a file into the current shell. Since each command in buildspec.yml gets a new shell, the variables loaded by source in one command won't be present in the next.

  • Choosing the Right Approach:

    • && for Simplicity: If you have a few related commands, chaining them with && is the most straightforward way to maintain environment variable consistency.
    • Scripts for Complexity: For longer sequences of commands or when you need more control flow (loops, conditional statements), using a separate script file is a better practice.

  • Shell Choice Matters: While the examples use Bash, CodeBuild supports other shells. Ensure your buildspec.yml specifies the correct shell (env: shells:) if your script relies on shell-specific syntax.

  • Debugging Tips:

    • Verbose Logging: Enable detailed logs in your CodeBuild project to inspect the environment variables available at each step.
    • Echo for Clarity: Add echo $MY_VAR (or similar) at different points in your buildspec.yml or script to track the variable's value.

  • Security Considerations: Be mindful of sensitive information in environment variables. Avoid hardcoding secrets in your buildspec.yml and explore CodeBuild's secrets management features for secure handling.

Summary

Problem Solution Explanation
Environment variables set by one command in buildspec.yml don't persist to subsequent commands. 1. Combine commands: Use && to chain commands within a single command entry.
2. Use a script: Place dependent commands within a script and execute it.		 Each command in buildspec.yml runs in a separate shell by default. Combining commands or using a script ensures all commands execute within the same shell, preserving environment variables.

Additional Notes:

  • If your script uses Bash-specific syntax, specify bash as your shell in the env section of your buildspec.yml.
  • Example: 
    version: 0.2
env:
  shells:
    - bash

Conclusion

By understanding the shell-based execution model of AWS CodeBuild and employing techniques like command chaining or script execution, you can ensure that your build processes have access to the correct environment variables. This control is essential for creating robust and predictable CI/CD pipelines within the AWS ecosystem. Remember to consult the AWS CodeBuild documentation for the most up-to-date information and best practices.

References

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