Resync mariadb and percona docs with mysql

This includes both `stack.yml` and the "Secrets" usage description.

mariadb/content.md

@@ -22,7 +22,9 @@ $ docker run --name some-%%REPO%% -e MYSQL_ROOT_PASSWORD=my-secret-pw -d %%REPO%
 
 ## Connect to MySQL from an application in another Docker container
 
-Since MariaDB is intended as a drop-in replacement for MySQL, it can be used with many applications. This image exposes the standard MySQL port (3306), so container linking makes the MySQL instance available to other application containers. Start your application container like this in order to link it to the MySQL container:
+Since MariaDB is intended as a drop-in replacement for MySQL, it can be used with many applications.
+
+This image exposes the standard MySQL port (3306), so container linking makes the MySQL instance available to other application containers. Start your application container like this in order to link it to the MySQL container:
 
 ```console
 $ docker run --name some-app --link some-%%REPO%%:mysql -d application-that-uses-mysql
@@ -46,6 +48,10 @@ $ docker run -it --rm %%REPO%% mysql -hsome.mysql.host -usome-mysql-user -p
 
 More information about the MySQL command line client can be found in the [MySQL documentation](http://dev.mysql.com/doc/en/mysql.html)
 
+## %%STACK%%
+
+Run `docker stack deploy -c stack.yml %%REPO%%` (or `docker-compose -f stack.yml up`), wait for it to initialize completely, and visit `http://swarm-ip:8080`, `http://localhost:8080`, or `http://host-ip:8080` (as appropriate).
+
 ## Container shell access and viewing MySQL logs
 
 The `docker exec` command allows you to run commands inside a Docker container. The following command line will give you a bash shell inside your `%%REPO%%` container:
@@ -118,6 +124,16 @@ This is an optional variable. Set to `yes` to allow the container to be started
 
 This is an optional variable. Set to `yes` to generate a random initial password for the root user (using `pwgen`). The generated root password will be printed to stdout (`GENERATED ROOT PASSWORD: .....`).
 
+## Docker Secrets
+
+As an alternative to passing sensitive information via environment variables, `_FILE` may be appended to the previously listed environment variables, causing the initialization script to load the values for those variables from files present in the container. In particular, this can be used to load passwords from Docker secrets stored in `/run/secrets/<secret_name>` files. For example:
+
+```console
+$ docker run --name some-mysql -e MYSQL_ROOT_PASSWORD_FILE=/run/secrets/mysql-root -d %%REPO%%:tag
+```
+
+Currently, this is only supported for `MYSQL_ROOT_PASSWORD`, `MYSQL_ROOT_HOST`, `MYSQL_DATABASE`, `MYSQL_USER`, and `MYSQL_PASSWORD`.
+
 # Initializing a fresh instance
 
 When a container is started for the first time, a new database with the specified name will be created and initialized with the provided configuration variables. Furthermore, it will execute files with extensions `.sh`, `.sql` and `.sql.gz` that are found in `/docker-entrypoint-initdb.d`. Files will be executed in alphabetical order. You can easily populate your %%REPO%% services by [mounting a SQL dump into that directory](https://docs.docker.com/engine/tutorials/dockervolumes/#mount-a-host-file-as-a-data-volume) and provide [custom images](https://docs.docker.com/reference/builder/) with contributed data. SQL files will be imported by default to the database specified by the `MYSQL_DATABASE` variable.

mariadb/stack.yml

@@ -0,0 +1,17 @@
+# Use root/example as user/password credentials
+version: '3.1'
+
+services:
+
+    db:
+        image: mariadb
+        restart: always
+        environment:
+            MYSQL_ROOT_PASSWORD: example
+
+    adminer:
+        image: adminer
+        restart: always
+        ports:
+            - 8080:8080
+

percona/content.md

@@ -22,7 +22,9 @@ $ docker run --name some-%%REPO%% -e MYSQL_ROOT_PASSWORD=my-secret-pw -d %%REPO%
 
 ## Connect to MySQL from an application in another Docker container
 
-Since Percona is intended as a drop-in replacement for MySQL, it can be used with many applications. This image exposes the standard MySQL port (3306), so container linking makes the MySQL instance available to other application containers. Start your application container like this in order to link it to the MySQL container:
+Since Percona is intended as a drop-in replacement for MySQL, it can be used with many applications.
+
+This image exposes the standard MySQL port (3306), so container linking makes the MySQL instance available to other application containers. Start your application container like this in order to link it to the MySQL container:
 
 ```console
 $ docker run --name some-app --link some-%%REPO%%:mysql -d application-that-uses-mysql
@@ -46,6 +48,10 @@ $ docker run -it --rm %%REPO%% mysql -hsome.mysql.host -usome-mysql-user -p
 
 More information about the MySQL command line client can be found in the [MySQL documentation](http://dev.mysql.com/doc/en/mysql.html)
 
+## %%STACK%%
+
+Run `docker stack deploy -c stack.yml %%REPO%%` (or `docker-compose -f stack.yml up`), wait for it to initialize completely, and visit `http://swarm-ip:8080`, `http://localhost:8080`, or `http://host-ip:8080` (as appropriate).
+
 ## Container shell access and viewing MySQL logs
 
 The `docker exec` command allows you to run commands inside a Docker container. The following command line will give you a bash shell inside your `%%REPO%%` container:
@@ -122,6 +128,16 @@ This is an optional variable. Set to `yes` to generate a random initial password
 
 Sets root (*not* the user specified in `MYSQL_USER`!) user as expired once init is complete, forcing a password change on first login. *NOTE*: This feature is supported on MySQL 5.6+ only. Using this option on MySQL 5.5 will throw an appropriate error during initialization.
 
+## Docker Secrets
+
+As an alternative to passing sensitive information via environment variables, `_FILE` may be appended to the previously listed environment variables, causing the initialization script to load the values for those variables from files present in the container. In particular, this can be used to load passwords from Docker secrets stored in `/run/secrets/<secret_name>` files. For example:
+
+```console
+$ docker run --name some-mysql -e MYSQL_ROOT_PASSWORD_FILE=/run/secrets/mysql-root -d %%REPO%%:tag
+```
+
+Currently, this is only supported for `MYSQL_ROOT_PASSWORD`, `MYSQL_ROOT_HOST`, `MYSQL_DATABASE`, `MYSQL_USER`, and `MYSQL_PASSWORD`.
+
 # Initializing a fresh instance
 
 When a container is started for the first time, a new database with the specified name will be created and initialized with the provided configuration variables. Furthermore, it will execute files with extensions `.sh`, `.sql` and `.sql.gz` that are found in `/docker-entrypoint-initdb.d`. Files will be executed in alphabetical order. You can easily populate your %%REPO%% services by [mounting a SQL dump into that directory](https://docs.docker.com/engine/tutorials/dockervolumes/#mount-a-host-file-as-a-data-volume) and provide [custom images](https://docs.docker.com/reference/builder/) with contributed data. SQL files will be imported by default to the database specified by the `MYSQL_DATABASE` variable.

percona/stack.yml

@@ -0,0 +1,17 @@
+# Use root/example as user/password credentials
+version: '3.1'
+
+services:
+
+    db:
+        image: percona
+        restart: always
+        environment:
+            MYSQL_ROOT_PASSWORD: example
+
+    adminer:
+        image: adminer
+        restart: always
+        ports:
+            - 8080:8080
+