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@@ -10,48 +10,120 @@ It aims to retain close compatibility to the official MySQL releases, while focu
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# How to use this image
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-## start a `%%REPO%%` server instance
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+## Start a `%%REPO%%` server instance
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+
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+Starting a Percona instance is simple:
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```console
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-$ docker run --name some-%%REPO%% -e MYSQL_ROOT_PASSWORD=mysecretpassword -d %%REPO%%
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+$ docker run --name some-%%REPO%% -e MYSQL_ROOT_PASSWORD=my-secret-pw -d %%REPO%%:tag
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```
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-This image includes `EXPOSE 3306` (the standard MySQL port), so container linking will make it automatically available to the linked containers (as the following examples illustrate).
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+... where `some-%%REPO%%` is the name you want to assign to your container, `my-secret-pw` is the password to be set for the MySQL root user and `tag` is the tag specifying the MySQL version you want. See the list above for relevant tags.
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-## connect to it from an application
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+## Connect to MySQL from an application in another Docker container
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-Since Percona Server is intended as a drop-in replacement for MySQL, it can be used with many applications.
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+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:
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```console
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$ docker run --name some-app --link some-%%REPO%%:mysql -d application-that-uses-mysql
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```
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-## ... or via `mysql`
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+## Connect to Percona from the MySQL command line client
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+
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+The following command starts another %%REPO%% container instance and runs the `mysql` command line client against your original %%REPO%% container, allowing you to execute SQL statements against your database instance:
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```console
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$ docker run -it --link some-%%REPO%%:mysql --rm %%REPO%% sh -c 'exec mysql -h"$MYSQL_PORT_3306_TCP_ADDR" -P"$MYSQL_PORT_3306_TCP_PORT" -uroot -p"$MYSQL_ENV_MYSQL_ROOT_PASSWORD"'
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```
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-## Environment Variables
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+... where `some-%%REPO%%` is the name of your original %%REPO%% container.
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+
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+More information about the MySQL command line client can be found in the [MySQL documentation](http://dev.mysql.com/doc/en/mysql.html)
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+
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+## Container shell access and viewing MySQL logs
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+
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+The `docker exec` command allows you to run commands inside a Docker container. The following command line will give you a bash shell inside your `%%REPO%%` container:
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+
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+```console
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+$ docker exec -it some-%%REPO%% bash
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+```
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+
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+The Percona Server log is available through Docker's container log:
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+
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+```console
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+$ docker logs some-%%REPO%%
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+```
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+
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+## Using a custom MySQL configuration file
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-The `%%REPO%%` image uses several environment variables which are easy to miss. While not all the variables are required, they may significantly aid you in using the image.
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+The Percona startup configuration is specified in the file `/etc/mysql/my.cnf`, and that file in turn includes any files found in the `/etc/mysql/conf.d` directory that end with `.cnf`. Settings in files in this directory will augment and/or override settings in `/etc/mysql/my.cnf`. If you want to use a customized MySQL configuration, you can create your alternative configuration file in a directory on the host machine and then mount that directory location as `/etc/mysql/conf.d` inside the `%%REPO%%` container.
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-The variable names are prefixed with `MYSQL_` since the binary is `mysqld`, and since the intention is to be a drop-in replacement for MySQL, as mentioned above.
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+If `/my/custom/config-file.cnf` is the path and name of your custom configuration file, you can start your `%%REPO%%` container like this (note that only the directory path of the custom config file is used in this command):
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+
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+```console
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+$ docker run --name some-%%REPO%% -v /my/custom:/etc/mysql/conf.d -e MYSQL_ROOT_PASSWORD=my-secret-pw -d %%REPO%%:tag
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+```
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+
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+This will start a new container `some-%%REPO%%` where the Percona instance uses the combined startup settings from `/etc/mysql/my.cnf` and `/etc/mysql/conf.d/config-file.cnf`, with settings from the latter taking precedence.
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+
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+Note that users on host systems with SELinux enabled may see issues with this. The current workaround is to assign the relevant SELinux policy type to your new config file so that the container will be allowed to mount it:
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+
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+```console
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+$ chcon -Rt svirt_sandbox_file_t /my/custom
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+```
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+
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+## Environment Variables
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+
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+When you start the `%%REPO%%` image, you can adjust the configuration of the Percona instance by passing one or more environment variables on the `docker run` command line. Do note that none of the variables below will have any effect if you start the container with a data directory that already contains a database: any pre-existing database will always be left untouched on container startup.
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### `MYSQL_ROOT_PASSWORD`
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-This is the one environment variable that is required. This environment variable should be what you want to set the password for the `root` user to be. In the above example, it is being set to "`mysecretpassword`".
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+This variable is mandatory and specifies the password that will be set for the Percona `root` superuser account. In the above example, it was set to `my-secret-pw`.
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+
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+### `MYSQL_DATABASE`
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+
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+This variable is optional and allows you to specify the name of a database to be created on image startup. If a user/password was supplied (see below) then that user will be granted superuser access ([corresponding to `GRANT ALL`](http://dev.mysql.com/doc/en/adding-users.html)) to this database.
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### `MYSQL_USER`, `MYSQL_PASSWORD`
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-These optional environment variables are used in conjunction to both create a new user and set that user's password, which will subsequently be granted all permissions for the database specified by the optional `MYSQL_DATABASE` variable. Note that if you only have one of these two environment variables, then neither will do anything -- these two are required to be used in conjunction with one another.
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+These variables are optional, used in conjunction to create a new user and to set that user's password. This user will be granted superuser permissions (see above) for the database specified by the `MYSQL_DATABASE` variable. Both variables are required for a user to be created.
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-Additionally, there is no need to specify `MYSQL_USER` with `root`, as the `root` user already exists by default, and the password of that user is controlled by `MYSQL_ROOT_PASSWORD` (see above).
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+Do note that there is no need to use this mechanism to create the root superuser, that user gets created by default with the password specified by the `MYSQL_ROOT_PASSWORD` variable.
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-### `MYSQL_DATABASE`
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+### `MYSQL_ALLOW_EMPTY_PASSWORD`
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-This optional environment variable denotes the name of a database to create. If a user/password was supplied (via the `MYSQL_USER` and `MYSQL_PASSWORD` environment variables) then that user will be granted (via `GRANT ALL`) access to this database.
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+This is an optional variable. Set to `yes` to allow the container to be started with a blank password for the root user. *NOTE*: Setting this variable to `yes` is not recommended unless you really know what you are doing, since this will leave your Percona instance completely unprotected, allowing anyone to gain complete superuser access.
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# Caveats
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+## Where to Store Data
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+
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+Important note: There are several ways to store data used by applications that run in Docker containers. We encourage users of the `%%REPO%%` images to familiarize themselves with the options available, including:
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+
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+- Let Docker manage the storage of your database data [by writing the database files to disk on the host system using its own internal volume management](https://docs.docker.com/userguide/dockervolumes/#adding-a-data-volume). This is the default and is easy and fairly transparent to the user. The downside is that the files may be hard to locate for tools and applications that run directly on the host system, i.e. outside containers.
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+- Create a data directory on the host system (outside the container) and [mount this to a directory visible from inside the container](https://docs.docker.com/userguide/dockervolumes/#mount-a-host-directory-as-a-data-volume). This places the database files in a known location on the host system, and makes it easy for tools and applications on the host system to access the files. The downside is that the user needs to make sure that the directory exists, and that e.g. directory permissions and other security mechanisms on the host system are set up correctly.
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+
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+The Docker documentation is a good starting point for understanding the different storage options and variations, and there are multiple blogs and forum postings that discuss and give advice in this area. We will simply show the basic procedure here for the latter option above:
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+
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+1. Create a data directory on a suitable volume on your host system, e.g. `/my/own/datadir`.
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+2. Start your `%%REPO%%` container like this:
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+
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+ ```console
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+ $ docker run --name some-%%REPO%% -v /my/own/datadir:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d %%REPO%%:tag
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+ ```
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+
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+The `-v /my/own/datadir:/var/lib/mysql` part of the command mounts the `/my/own/datadir` directory from the underlying host system as `/var/lib/mysql` inside the container, where MySQL by default will write its data files.
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+
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+Note that users on host systems with SELinux enabled may see issues with this. The current workaround is to assign the relevant SELinux policy type to the new data directory so that the container will be allowed to access it:
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+
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+```console
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+$ chcon -Rt svirt_sandbox_file_t /my/own/datadir
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+```
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+
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+## No connections until MySQL init completes
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+
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If there is no database initialized when the container starts, then a default database will be created. While this is the expected behavior, this means that it will not accept incoming connections until such initialization completes. This may cause issues when using automation tools, such as `docker-compose`, which start several containers simultaneously.
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+
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+## Usage against an existing database
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+
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+If you start your `%%REPO%%` container instance with a data directory that already contains a database (specifically, a `mysql` subdirectory), the `$MYSQL_ROOT_PASSWORD` variable should be omitted from the run command line; it will in any case be ignored, and the pre-existing database will not be changed in any way.
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Joe Ferguson