MySQL - Database Images | Using Images

Overview
Versions
Images
Configuration and Usage
Creating a Database Service from a Template
Troubleshooting
- Linux Native AIO Failure

Overview

OpenShift Online provides a container image for running MySQL. This image can provide database services based on username, password, and database name settings provided via configuration.

Versions

Currently, OpenShift Online provides versions 5.6 and 5.7 of MySQL.

Images

RHEL 7 images are available through the Red Hat Registry:

$ docker pull registry.redhat.io/rhscl/mysql-56-rhel7
$ docker pull registry.redhat.io/rhscl/mysql-57-rhel7

You can use these images through the mysql image stream.

Configuration and Usage

Initializing the Database

The first time you use the shared volume, the database is created along with the database administrator user and the MySQL root user (if you specify the MYSQL_ROOT_PASSWORD environment variable). Afterwards, the MySQL daemon starts up. If you are re-attaching the volume to another container, then the database, database user, and the administrator user are not created, and the MySQL daemon starts.

The following command creates a new database pod with MySQL running in a container:

$ oc new-app \
    -e MYSQL_USER=<username> \
    -e MYSQL_PASSWORD=<password> \
    -e MYSQL_DATABASE=<database_name> \
    mysql:5.6

Running MySQL Commands in Containers

OpenShift Online uses Software Collections (SCLs) to install and launch MySQL. If you want to execute a MySQL command inside of a running container (for debugging), you must invoke it using bash.

To do so, first identify the name of the pod. For example, you can view the list of pods in your current project:

$ oc get pods

Then, open a remote shell session to the pod:

$ oc rsh <pod>

When you enter the container, the required SCL is automatically enabled.

You can now run the mysql command from the bash shell to start a MySQL interactive session and perform normal MySQL operations. For example, to authenticate as the database user:

bash-4.2$ mysql -u $MYSQL_USER -p$MYSQL_PASSWORD -h $HOSTNAME $MYSQL_DATABASE
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.6.37 MySQL Community Server (GPL)
...
mysql>

When you are finished, enter quit or exit to leave the MySQL session.

Environment Variables

The MySQL user name, password, and database name must be configured with the following environment variables:

Table 1. MySQL Environment Variables
Variable Name	Description
`MYSQL_USER`	Specifies the user name for the database user that is created for use by your application.
`MYSQL_PASSWORD`	Password for the `MYSQL_USER`.
`MYSQL_DATABASE`	Name of the database to which `MYSQL_USER` has full rights.
`MYSQL_ROOT_PASSWORD`	Optional password for the root user. If this is not set, then remote login to the root account is not possible. Local connections from within the container are always permitted without a password.
`MYSQL_SERVICE_HOST`	Service host variable automatically created by Kubernetes.
`MYSQL_SERVICE_PORT`	Service port variable automatically created by Kubernetes.

You must specify the user name, password, and database name. If you do not specify all three, the pod will fail to start and OpenShift Online will continuously try to restart it.

MySQL settings can be configured with the following environment variables:

Table 2. Additional MySQL Settings
Variable Name	Description	Default
`MYSQL_LOWER_CASE_TABLE_NAMES`	Sets how the table names are stored and compared.	0
`MYSQL_MAX_CONNECTIONS`	The maximum permitted number of simultaneous client connections.	151
`MYSQL_MAX_ALLOWED_PACKET`	The maximum size of one packet or any generated/intermediate string.	200M
`MYSQL_FT_MIN_WORD_LEN`	The minimum length of the word to be included in a FULLTEXT index.	4
`MYSQL_FT_MAX_WORD_LEN`	The maximum length of the word to be included in a FULLTEXT index.	20
`MYSQL_AIO`	Controls the innodb_use_native_aio setting value if the native AIO is broken.	1
`MYSQL_TABLE_OPEN_CACHE`	The number of open tables for all threads.	400
`MYSQL_KEY_BUFFER_SIZE`	The size of the buffer used for index blocks.	10% of available memory
`MYSQL_SORT_BUFFER_SIZE`	The size of the buffer used for sorting.	256K
`MYSQL_READ_BUFFER_SIZE`	The size of the buffer used for a sequential scan.	5% of available memory
`MYSQL_INNODB_BUFFER_POOL_SIZE`	The size of the buffer pool where InnoDB caches table and index data.	50% of available memory
`MYSQL_INNODB_LOG_FILE_SIZE`	The size of each log file in a log group.	15% of available memory
`MYSQL_INNODB_LOG_BUFFER_SIZE`	The size of the buffer that InnoDB uses to write to the log files on disk.	15% of available memory

Some of the memory-related parameters have percentages as default values. These values are calculated dynamically during a container’s startup based on memory limits.

Volume Mount Points

The MySQL image can be run with mounted volumes to enable persistent storage for the database:

/var/lib/mysql/data - This is the data directory where MySQL stores database files.

Changing Passwords

Passwords are part of the image configuration, therefore the only supported method to change passwords for the database user (MYSQL_USER) and root user is by changing the environment variables MYSQL_PASSWORD and MYSQL_ROOT_PASSWORD, respectively.

You can view the current passwords by viewing the pod or deployment configuration in the web console or by listing the environment variables with the CLI:

$ oc set env pod <pod_name> --list

Whenever MYSQL_ROOT_PASSWORD is set, it enables remote access for the root user with the given password, and whenever it is unset, remote access for the root user is disabled. This does not affect the regular user MYSQL_USER, who always has remote access. This also does not affect local access by the root user, who can always log in without a password in localhost.

Changing database passwords through SQL statements or any way other than through the environment variables aforementioned causes a mismatch between the values stored in the variables and the actual passwords. Whenever a database container starts, it resets the passwords to the values stored in the environment variables.

To change these passwords, update one or both of the desired environment variables for the related deployment configuration(s) using the oc set env command. If multiple deployment configurations utilize these environment variables, for example in the case of an application created from a template, you must update the variables on each deployment configuration so that the passwords are in sync everywhere. This can be done all in the same command:

$ oc set env dc <dc_name> [<dc_name_2> ...] \
  MYSQL_PASSWORD=<new_password> \
  MYSQL_ROOT_PASSWORD=<new_root_password>

Depending on your application, there may be other environment variables for passwords in other parts of the application that should also be updated to match. For example, there could be a more generic DATABASE_USER variable in a front-end pod that should match the database user’s password. Ensure that passwords are in sync for all required environment variables per your application, otherwise your pods may fail to redeploy when triggered.

Updating the environment variables triggers the redeployment of the database server if you have a configuration change trigger. Otherwise, you must manually start a new deployment in order to apply the password changes.

To verify that new passwords are in effect, first open a remote shell session to the running MySQL pod:

$ oc rsh <pod>

From the bash shell, verify the database user’s new password:

bash-4.2$ mysql -u $MYSQL_USER -p<new_password> -h $HOSTNAME $MYSQL_DATABASE -te "SELECT * FROM (SELECT database()) db CROSS JOIN (SELECT user()) u"

If the password was changed correctly, you should see a table like this:

+------------+---------------------+
| database() | user()              |
+------------+---------------------+
| sampledb   | user0PG@172.17.42.1 |
+------------+---------------------+

To verify the root user’s new password:

bash-4.2$ mysql -u root -p<new_root_password> -h $HOSTNAME $MYSQL_DATABASE -te "SELECT * FROM (SELECT database()) db CROSS JOIN (SELECT user()) u"

If the password was changed correctly, you should see a table like this:

+------------+------------------+
| database() | user()           |
+------------+------------------+
| sampledb   | root@172.17.42.1 |
+------------+------------------+

Creating a Database Service from a Template

OpenShift Online provides a template to make creating a new database service easy. The template provides parameter fields to define all the mandatory environment variables (user, password, database name, etc) with predefined defaults including auto-generation of password values. It will also define both a deployment configuration and a service.

The MySQL template should have been registered in the default openshift project by your cluster administrator during the initial cluster setup.

The following template is available:

mysql-persistent uses a persistent volume store for the database data which means the data will survive a pod restart.

You can instantiate templates by following these instructions.

Once you have instantiated the service, you can copy the user name, password, and database name environment variables into a deployment configuration for another component that intends to access the database. That component can then access the database via the service that was defined.

Creating the Deployment Configuration for the MySQL Master

To set up MySQL replication, a deployment configuration is defined in the example template that defines a replication controller. For MySQL master-slave replication, two deployment configurations are needed. One deployment configuration defines the MySQL master server and second the MySQL slave servers.

To tell a MySQL server to act as the master, the command field in the container’s definition in the deployment configuration must be set to run-mysqld-master. This script acts as an alternative entrypoint for the MySQL image and configures the MySQL server to run as the master in replication.

MySQL replication requires a special user that relays data between the master and slaves. The following environment variables are defined in the template for this purpose:

Variable Name Description Default

Variable Name	Description	Default
`MYSQL_MASTER_USER`	The user name of the replication user	master
`MYSQL_MASTER_PASSWORD`	The password for the replication user	generated

MYSQL_MASTER_USER

The user name of the replication user

master

MYSQL_MASTER_PASSWORD

The password for the replication user

generated

Example 1. MySQL Master Deployment Configuration Object Definition in the Example Template

kind: "DeploymentConfig"
apiVersion: "v1"
metadata:
  name: "mysql-master"
spec:
  strategy:
    type: "Recreate"
  triggers:
    - type: "ConfigChange"
  replicas: 1
  selector:
    name: "mysql-master"
  template:
    metadata:
      labels:
        name: "mysql-master"
    spec:
      volumes:
        - name: "mysql-master-data"
          persistentVolumeClaim:
            claimName: "mysql-master"
      containers:
        - name: "server"
          image: "openshift/mysql-56-centos7"
          command:
            - "run-mysqld-master"
          ports:
            - containerPort: 3306
              protocol: "TCP"
          env:
            - name: "MYSQL_MASTER_USER"
              value: "${MYSQL_MASTER_USER}"
            - name: "MYSQL_MASTER_PASSWORD"
              value: "${MYSQL_MASTER_PASSWORD}"
            - name: "MYSQL_USER"
              value: "${MYSQL_USER}"
            - name: "MYSQL_PASSWORD"
              value: "${MYSQL_PASSWORD}"
            - name: "MYSQL_DATABASE"
              value: "${MYSQL_DATABASE}"
            - name: "MYSQL_ROOT_PASSWORD"
              value: "${MYSQL_ROOT_PASSWORD}"
          volumeMounts:
            - name: "mysql-master-data"
              mountPath: "/var/lib/mysql/data"
          resources: {}
          terminationMessagePath: "/dev/termination-log"
          imagePullPolicy: "IfNotPresent"
          securityContext:
            capabilities: {}
            privileged: false
      restartPolicy: "Always"
      dnsPolicy: "ClusterFirst"

After the deployment configuration is created and the pod with MySQL master server is started, it will create the database defined by MYSQL_DATABASE and configure the server to replicate this database to slaves.

The example provided defines only one replica of the MySQL master server. This causes OpenShift Online to start only one instance of the server. Multiple instances (multi-master) is not supported and therefore you can not scale this replication controller.

To replicate the database created by the MySQL master, a deployment configuration is defined in the template. This deployment configuration creates a replication controller that launches the MySQL image with the command field set to run-mysqld-slave. This alternative entrypoints skips the initialization of the database and configures the MySQL server to connect to the mysql-master service, which is also defined in example template.

Example 2. MySQL Slave Deployment Configuration Object Definition in the Example Template

kind: "DeploymentConfig"
apiVersion: "v1"
metadata:
  name: "mysql-slave"
spec:
  strategy:
    type: "Recreate"
  triggers:
    - type: "ConfigChange"
  replicas: 1
  selector:
    name: "mysql-slave"
  template:
    metadata:
      labels:
        name: "mysql-slave"
    spec:
      containers:
        - name: "server"
          image: "openshift/mysql-56-centos7"
          command:
            - "run-mysqld-slave"
          ports:
            - containerPort: 3306
              protocol: "TCP"
          env:
            - name: "MYSQL_MASTER_USER"
              value: "${MYSQL_MASTER_USER}"
            - name: "MYSQL_MASTER_PASSWORD"
              value: "${MYSQL_MASTER_PASSWORD}"
            - name: "MYSQL_DATABASE"
              value: "${MYSQL_DATABASE}"
          resources: {}
          terminationMessagePath: "/dev/termination-log"
          imagePullPolicy: "IfNotPresent"
          securityContext:
            capabilities: {}
            privileged: false
      restartPolicy: "Always"
      dnsPolicy: "ClusterFirst"

This example deployment configuration starts the replication controller with the initial number of replicas set to 1. You can scale this replication controller in both directions, up to the resources capacity of your account.

Creating a Headless Service

The pods created by the MySQL slave replication controller must reach the MySQL master server in order to register for replication. The example template defines a headless service named mysql-master for this purpose. This service is not used only for replication, but the clients can also send the queries to mysql-master:3306 as the MySQL host.

To have a headless service, the clusterIP parameter in the service definition is set to None. Then you can use a DNS query to get a list of the pod IP addresses that represents the current endpoints for this service.

Example 3. Headless Service Object Definition in the Example Template

kind: "Service"
apiVersion: "v1"
metadata:
  name: "mysql-master"
  labels:
    name: "mysql-master"
spec:
  ports:
    - protocol: "TCP"
      port: 3306
      targetPort: 3306
      nodePort: 0
  selector:
    name: "mysql-master"
  clusterIP: "None"
  type: "ClusterIP"
  sessionAffinity: "None"
status:
  loadBalancer: {}

Scaling the MySQL Slaves

To increase the number of members in the cluster:

$ oc scale rc mysql-slave-1 --replicas=<number>

This tells the replication controller to create a new MySQL slave pod. When a new slave is created, the slave entrypoint first attempts to contact the mysql-master service and register itself to the replication set. Once that is done, the MySQL master server sends the slave the replicated database.

When scaling down, the MySQL slave is shut down and, because the slave does not have any persistent storage defined, all data on the slave is lost. The MySQL master server then discovers that the slave is not reachable anymore, and it automatically removes it from the replication.

Troubleshooting

This section describes some troubles you might encounter and presents possible resolutions.

Linux Native AIO Failure

Symptom

The MySQL container fails to start and the logs show something like:

151113  5:06:56 InnoDB: Using Linux native AIO
151113  5:06:56  InnoDB: Warning: io_setup() failed with EAGAIN. Will make 5 attempts before giving up.
InnoDB: Warning: io_setup() attempt 1 failed.
InnoDB: Warning: io_setup() attempt 2 failed.
Waiting for MySQL to start ...
InnoDB: Warning: io_setup() attempt 3 failed.
InnoDB: Warning: io_setup() attempt 4 failed.
Waiting for MySQL to start ...
InnoDB: Warning: io_setup() attempt 5 failed.
151113  5:06:59  InnoDB: Error: io_setup() failed with EAGAIN after 5 attempts.
InnoDB: You can disable Linux Native AIO by setting innodb_use_native_aio = 0 in my.cnf
151113  5:06:59 InnoDB: Fatal error: cannot initialize AIO sub-system
151113  5:06:59 [ERROR] Plugin 'InnoDB' init function returned error.
151113  5:06:59 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
151113  5:06:59 [ERROR] Unknown/unsupported storage engine: InnoDB
151113  5:06:59 [ERROR] Aborting

Explanation

MySQL’s storage engine was unable to use the kernel’s AIO (Asynchronous I/O) facilities due to resource limits.

Resolution

Turn off AIO usage entirely by setting environment variable MYSQL_AIO to have value 0. On subsequent deployments, this arranges for the MySQL configuration variable innodb_use_native_aio to have value 0.