How to track constant changes in multi-environment deployment

M66 2025-05-23

In PHP development, the use of constants is inevitable, and they are often used to store fixed values shared in multiple locations in the application. In multi-environment deployments (such as development environments, test environments, and production environments), the values of constants may vary. How to effectively track changes in constants to ensure correct configuration in different environments? An effective method is to use PHP's get_defined_constants function, which is able to list all currently defined constants. This article will introduce how to track changes in PHP constants through this function to ensure the stability of applications in multi-environment deployment.

1. Introduction to get_defined_constants function

The get_defined_constants function in PHP is used to return an associative array containing all defined constants. The function signature is as follows:

 array get_defined_constants(bool $categorize = false)

$categorize parameter: default is false , indicating that all constants are returned. If set to true , constants are divided into two categories: built-in constants and user-defined constants.

2. Necessity to monitor constant changes

In multi-environment deployments, the values of constants are usually environment-dependent. For example, there may be some debug constants in a development environment, which should not be enabled in a production environment. Therefore, when the constant value changes, we need to be able to detect and record it to ensure that there is no wrong constant settings in production.

3. How to use get_defined_constants function to track constants

Through the get_defined_constants function, we can get all the constants defined in the current environment and compare them with other environments to track the changes in the constant value.

Sample code:

 <?php

// Get all constants in the current environment
$current_constants = get_defined_constants(true);

// Suppose you have two environment variables：Development Environment（dev）and production environment（prod）
$env_constants = [
    'dev' => [
        'DEBUG_MODE' => true,
        'DATABASE_HOST' => 'dev.db.m66.net',
    ],
    'prod' => [
        'DEBUG_MODE' => false,
        'DATABASE_HOST' => 'prod.db.m66.net',
    ]
];

// Compare constant changes
function compare_constants($env, $current_constants, $env_constants) {
    echo "environment: $env\n";
    echo "Change constants:\n";
    
    foreach ($env_constants as $constant => $value) {
        if (isset($current_constants[$constant])) {
            if ($current_constants[$constant] !== $value) {
                echo "constant $constant Changes: from {$value} Become {$current_constants[$constant]}\n";
            }
        } else {
            echo "constant $constant 在当前environment中未定义\n";
        }
    }
}

// 比较Development Environment
compare_constants('dev', $current_constants['user'], $env_constants['dev']);

// 比较生产environment
compare_constants('prod', $current_constants['user'], $env_constants['prod']);

?>

4. Record constant changes

In order to further track the changes in constants, we can record the changes in the log file for easier subsequent viewing and analysis. You can change the output part of the constant change in the above code to write to the log file.

 function log_constant_changes($message) {
    $logfile = '/path/to/your/log/file.log'; // Replace with your log file path
    file_put_contents($logfile, $message, FILE_APPEND);
}

function compare_constants_and_log($env, $current_constants, $env_constants) {
    $log_message = "environment: $env\nChange constants:\n";
    
    foreach ($env_constants as $constant => $value) {
        if (isset($current_constants[$constant])) {
            if ($current_constants[$constant] !== $value) {
                $log_message .= "constant $constant Changes: from {$value} Become {$current_constants[$constant]}\n";
            }
        } else {
            $log_message .= "constant $constant 在当前environment中未定义\n";
        }
    }
    
    log_constant_changes($log_message);
}

// 记录Development Environment的constant变化
compare_constants_and_log('dev', $current_constants['user'], $env_constants['dev']);

// 记录生产environment的constant变化
compare_constants_and_log('prod', $current_constants['user'], $env_constants['prod']);

5. Summary

Through the get_defined_constants function, we can easily obtain all the constants defined in the current environment, and help us discover the changes of constants in different environments by comparing the values of constants in different environments. Logging constant changes to log files not only helps developers track problems during debugging, but also ensures that the configuration of constants does not change unexpectedly during multi-environment deployment.

The above example demonstrates how to track changes in PHP constants in multi-environment deployments by simulating constant changes in development and production environments. This approach is ideal for large projects, ensuring constant correctness and consistency in different deployment environments.

get_defined_constants