Troubleshooting parameter handling issues - AWS Systems Manager
Common parameter handling issuesParameter validation tips

Troubleshooting parameter handling issues

Common parameter handling issues

Environment variables not available during execution

Problem: Commands fail because environment variables (SSM_parameter-name) are not found.

Possible causes:

  • SSM Agent version doesn't support environment variable interpolation

  • interpolationType is not set to ENV_VAR

  • Parameter name doesn't match the expected environment variable name

Solution:

  • Verify SSM Agent version is 3.3.2746.0 or later

  • Add fallback logic for older agent versions:

    if [ -z "${SSM_parameterName+x}" ]; then
    export SSM_parameterName="{{parameterName}}"
fi
Parameter values containing special characters

Problem: Commands fail when parameter values contain spaces, quotes, or other special characters.

Solution:

  • Use proper quoting when referencing environment variables:

    # Correct
echo "$SSM_parameter-name"

# Incorrect
echo $SSM_parameter-name

  • Add input validation using allowedPattern to restrict special characters

Inconsistent behavior across platforms

Problem: Parameter handling works differently on Linux and Windows Server systems.

Solution:

  • Use platform-specific environment variable syntax:

    # PowerShell
$env:SSM_parameter-name

# Bash
$SSM_parameter-name

  • Use platform-specific precondition checks in your document

Parameter values not properly escaped

Problem: Command injection vulnerabilities despite using environment variable interpolation.

Solution:

  • Always use proper escaping when including parameter values in commands:

    # Correct
mysql_command="mysql -u \"$SSM_username\" -p\"$SSM_password\""

# Incorrect
mysql_command="mysql -u $SSM_username -p$SSM_password"

Parameter validation tips

Use these techniques to validate your parameter handling:

  1. Test environment variable availability:

    #!/bin/bash
# Print all SSM_ environment variables
env | grep ^SSM_

# Test specific parameter
if [ -n "$SSM_parameter" ]; then
    echo "Parameter is available"
else
    echo "Parameter is not available"
fi

  2. Verify parameter patterns:

    parameters:
  myParameter:
    type: String
    allowedPattern: "^[a-zA-Z0-9_-]+$"
    description: "Test this pattern with sample inputs"

  3. Include error handling:

    if [[ ! "$SSM_parameter" =~ ^[a-zA-Z0-9_-]+$ ]]; then
    echo "Parameter validation failed"
    exit 1
fi