diff --git a/.docker/php/conf.d/local.ini b/.docker/php/conf.d/local.ini
index 12d22cc68..77b6daf00 100644
--- a/.docker/php/conf.d/local.ini
+++ b/.docker/php/conf.d/local.ini
@@ -2,7 +2,7 @@ expose_php = Off
 error_reporting = E_ALL
 display_errors = Off
 log_errors = On
-error_log = syslog
+error_log = /dev/stderr
 date.timezone = UTC
 allow_url_fopen = On
 post_max_size = 30M
diff --git a/.docker/php/php-fpm.conf b/.docker/php/php-fpm.conf
index 0e5eab212..6a9c64594 100644
--- a/.docker/php/php-fpm.conf
+++ b/.docker/php/php-fpm.conf
@@ -5,6 +5,10 @@ daemonize = no
 
 [www]
 env[DATABASE_URL] = $DATABASE_URL
+env[DEBUG] = $DEBUG
+env[DEBUG_FILE] = $DEBUG_FILE
+
+catch_workers_output = yes
 user = nginx
 group = nginx
 listen.owner = nginx
diff --git a/app/constants.php b/app/constants.php
index 011fa784a..4201e6e4c 100644
--- a/app/constants.php
+++ b/app/constants.php
@@ -1,8 +1,8 @@
 <?php
 
 // Enable/disable debug
-defined('DEBUG') or define('DEBUG', false);
-defined('DEBUG_FILE') or define('DEBUG_FILE', __DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'data'.DIRECTORY_SEPARATOR.'debug.log');
+defined('DEBUG') or define('DEBUG', getenv('DEBUG'));
+defined('DEBUG_FILE') or define('DEBUG_FILE', getenv('DEBUG_FILE') ?: __DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'data'.DIRECTORY_SEPARATOR.'debug.log');
 
 // Plugin directory
 defined('PLUGINS_DIR') or define('PLUGINS_DIR', __DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'plugins');
@@ -80,7 +80,7 @@ defined('ENABLE_HSTS') or define('ENABLE_HSTS', true);
 defined('ENABLE_XFRAME') or define('ENABLE_XFRAME', true);
 
 // Syslog
-defined('ENABLE_SYSLOG') or define('ENABLE_SYSLOG', true);
+defined('ENABLE_SYSLOG') or define('ENABLE_SYSLOG', getenv('ENABLE_SYSLOG'));
 
 // Default files directory
 defined('FILES_DIR') or define('FILES_DIR', 'data'.DIRECTORY_SEPARATOR.'files');
diff --git a/doc/docker.markdown b/doc/docker.markdown
index 6bd966d37..3f13e9545 100644
--- a/doc/docker.markdown
+++ b/doc/docker.markdown
@@ -69,6 +69,18 @@ You can attach 2 volumes to your container:
 
 Use the flag `-v` to mount a volume on the host machine like described in [official Docker documentation](https://docs.docker.com/engine/userguide/containers/dockervolumes/).
 
+Upgrade your container
+----------------------
+
+- Pull the new image
+- Remove the old container
+- Restart a new container with the same volumes
+
+Environment variables
+---------------------
+
+The list of environment variables is available on [this page](env.markdown).
+
 Config files
 ------------
 
diff --git a/doc/env.markdown b/doc/env.markdown
new file mode 100644
index 000000000..a01d0a6f4
--- /dev/null
+++ b/doc/env.markdown
@@ -0,0 +1,11 @@
+Environment Variables
+=====================
+
+Environment variables maybe useful when Kanboard is deployed as container (Docker).
+
+| Variable      | Description                                                                                                                     |
+|---------------|---------------------------------------------------------------------------------------------------------------------------------|
+| DATABASE_URL  | `[database type]://[username]:[password]@[host]:[port]/[database name]`, example: `postgres://foo:foo@myserver:5432/kanboard`   |
+| DEBUG         | Enable/Disable debug mode                                                                                                       |
+| DEBUG_FILE    | Debug file location, `DEBUG_FILE=php://stderr`                                                                                  |
+| ENABLE_SYSLOG | Enable/Disable logging to Syslog: `ENABLE_SYSLOG=1`                                                                             |
diff --git a/doc/index.markdown b/doc/index.markdown
index 99ca01f62..7a3ca8e59 100644
--- a/doc/index.markdown
+++ b/doc/index.markdown
@@ -105,6 +105,7 @@ Technical details
 
 - [Daily background job](cronjob.markdown)
 - [Config file](config.markdown)
+- [Environment variables](env.markdown)
 - [Email configuration](email-configuration.markdown)
 - [URL rewriting](nice-urls.markdown)