symfony · javiereguiluz · Apr 8, 2019 · Apr 8, 2019 · Apr 8, 2019 · Apr 9, 2019
diff --git a/reference/configuration/kernel.rst b/reference/configuration/kernel.rst
@@ -16,15 +16,19 @@ Configuration
 * `Root Directory`_
 * `Cache Directory`_
 * `Log Directory`_
+* `Container Build Time`_
 
 Charset
 ~~~~~~~
 
 **type**: ``string`` **default**: ``UTF-8``
 
-This returns the charset that is used in the application. To change it,
-override the :method:`Symfony\\Component\\HttpKernel\\Kernel::getCharset`
-method and return another charset, for instance::
+This option defines the charset that is used in the application. This value is
+exposed via the ``kernel.charset`` configuration parameter and the
+:method:`Symfony\\Component\\HttpKernel\\Kernel::getCharset` method.
+
+To change this value, override the ``getCharset()`` method and return another
+charset::
 
     // app/AppKernel.php
 
@@ -43,16 +47,18 @@ Kernel Name
 **type**: ``string`` **default**: ``app`` (i.e. the directory name holding
 the kernel class)
 
-To change this setting, override the :method:`Symfony\\Component\\HttpKernel\\Kernel::getName`
-method. Alternatively, move your kernel into a different directory. For
-example, if you moved the kernel into a ``foo`` directory (instead of ``app``),
-the kernel name will be ``foo``.
-
 The name of the kernel isn't usually directly important - it's used in the
 generation of cache files. If you have an application with multiple kernels,
 the easiest way to make each have a unique name is to duplicate the ``app``
 directory and rename it to something else (e.g. ``foo``).
 
+This value is exposed via the ``kernel.name`` configuration parameter and the
+:method:`Symfony\\Component\\HttpKernel\\Kernel::getName` method.
+
+To change this setting, override the ``getName()`` method. Alternatively, move
+your kernel into a different directory. For example, if you moved the kernel
+into a ``foo`` directory (instead of ``app``), the kernel name will be ``foo``.
+
 Root Directory
 ~~~~~~~~~~~~~~
 
@@ -63,11 +69,13 @@ Root Directory
 
 **type**: ``string`` **default**: the directory of ``AppKernel``
 
-This returns the root directory of your kernel. If you use the Symfony Standard
-edition, the root directory refers to the ``app`` directory.
+This returns the absolute path of the directory where your kernel class is
+located. If you use the Symfony Standard edition, this is the ``app/`` directory
+of your project.
 
-To change this setting, override the
-:method:`Symfony\\Component\\HttpKernel\\Kernel::getRootDir` method::
+This value is exposed via the ``kernel.root_dir`` configuration parameter and
+the :method:`Symfony\\Component\\HttpKernel\\Kernel::getRootDir` method. To
+change this setting, override the ``getRootDir()`` method::
 
     // app/AppKernel.php
 
@@ -91,12 +99,14 @@ Project Directory
 
 **type**: ``string`` **default**: the directory of the project ``composer.json``
 
-This returns the root directory of your Symfony project. It's calculated as
-the directory where the main ``composer.json`` file is stored.
+This returns the absolute path of the root directory of your Symfony project.
+It's calculated automatically as the directory where the main ``composer.json``
+file is stored.
 
-If for some reason the ``composer.json`` file is not stored at the root of your
-project, you can override the :method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir`
-method to return the right project directory::
+This value is exposed via the ``kernel.project_dir`` configuration parameter and
+the :method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir` method. To
+change this setting, override the ``getProjectDir()`` method to return the right
+project directory::
 
     // app/AppKernel.php
 
@@ -116,15 +126,84 @@ Cache Directory
 
 **type**: ``string`` **default**: ``$this->rootDir/cache/$this->environment``
 
-This returns the path to the cache directory. To change it, override the
-:method:`Symfony\\Component\\HttpKernel\\Kernel::getCacheDir` method. Read
-":ref:`override-cache-dir`" for more information.
+This returns the absolute path of the cache directory of your Symfony project.
+It's calculated automatically based on the current
+:doc:`environment </configuration/environments>`.
+
+This value is exposed via the ``kernel.cache_dir`` configuration parameter and
+the :method:`Symfony\\Component\\HttpKernel\\Kernel::getCacheDir` method. To
+change this setting, override the ``getCacheDir()`` method to return the right
+cache directory.
 
 Log Directory
 ~~~~~~~~~~~~~
 
 **type**: ``string`` **default**: ``$this->rootDir/logs``
 
-This returns the path to the log directory. To change it, override the
-:method:`Symfony\\Component\\HttpKernel\\Kernel::getLogDir` method. Read
-":ref:`override-logs-dir`" for more information.
+This returns the absolute path of the log directory of your Symfony project.
+It's calculated automatically based on the current
+:doc:`environment </configuration/environments>`.
+
+This value is exposed via the ``kernel.log_dir`` configuration parameter and
+the :method:`Symfony\\Component\\HttpKernel\\Kernel::getLogDir` method. To
+change this setting, override the ``getLogDir()`` method to return the right
+log directory.
+
+Container Build Time
+~~~~~~~~~~~~~~~~~~~~
+
+**type**: ``string`` **default**: the result of executing ``time()``
+
+Symfony follows the `reproducible builds`_ philosophy, which ensures that the
+result of compiling the exact same source code doesn't produce different
+results. This helps checking that a given binary or executable code was compiled
+from some trusted source code.
+
+In practice, the compiled :doc:`service container </service_container>` of your
+application will always be the same if you don't change its source code. This is
+exposed via these configuration parameters:
+
+* ``container.build_hash``, a hash of the contents of all your source files;
+* ``container.build_time``, a timestamp of the moment when the container was
+  built (the result of executing PHP's :phpfunction:`time` function);
+* ``container.build_id``, the result of merging the two previous parameters and
+  encoding the result using CRC32.
+
+Since the ``container.build_time`` value will change every time you compile the
+application, the build will not be strictly reproducible. If you care about
+this, the solution is to use another configuration parameter called
+``kernel.container_build_time`` and set it to a non-changing build time to
+achieve a strict reproducible build::
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # app/config/services.yml
+        parameters:
+            # ...
+            kernel.container_build_time: '1234567890'
+
+    .. code-block:: xml
+
+        <!-- app/config/services.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <container xmlns="http://symfony.com/schema/dic/services"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd">
+
+            <parameters>
+                <!-- ... -->
+                <parameter key="kernel.container_build_time">1234567890</parameter>
+            </parameters>
+        </container>
+
+    .. code-block:: php
+
+        // app/config/services.php
+        use Symfony\Component\DependencyInjection\Reference;
+
+        // ...
+        $container->setParameter('kernel.container_build_time', '1234567890');
+
+.. _`reproducible builds`: https://en.wikipedia.org/wiki/Reproducible_builds