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MariaDb Galera Cluster

This Docker container is based on the official Docker mariadb image and is designed to be compatible with auto-scheduling systems, specifically Kubernetes, Docker Swarm Mode and Kontena Classic. It could also work with manual scheduling (docker run) by specifying the correct environment variables or possibly other scheduling systems that use similar conventions.

Tags

It is recommended to test all upgrades carefully! The latest tag should not be used for production!

Several version are supported and rebuilt and tagged occasionally with both a version number and date built so just use the latest build for your major version that suits you or build your own version. Be sure to test replication functionality when building new versions using the test.sh script!

How It Works

This is not a simple config update, much effort has gone into making this container automate the initialization and recovery of a cluster. The entrypoint script orchestrates full recovery on simultaneous reset by having nodes communicate with each other before starting the mysqld process to ensure that the cluster is recovered correctly. It does this by examining Galera's state files, recovering the GTID position on all nodes and then communicating this between nodes to find the most up-to-date one to form a new cluster if needed. It also provides multiple healthcheck endpoints for varying degress of healthiness to aid with integration of load balancers and scheduling systems.

Examples

Please submit more examples for Mesos, etc. and also improvements for existing examples!

By using DNS resolution to discover other nodes, they don't have to be specified explicitly so this container should work with any system with DNS-based service discovery such as Kubernetes, Docker Swarm, Consul, etc.

Commands

The entrypoint takes as a command one of the following startup "modes". Additional arguments will be passed to the mysqld command line. For example, you will typically want to add --log-bin=mysqld-bin to enable binary logging.

seed

Used only to initialize a new cluster and after initialization and other nodes are joined the "seed" container should be stopped and replaced with a "node" container using the same volume.

node

Join an existing cluster. Takes as a second argument a comma-separated list of IPs or hostnames to resolve which are used to build the --wsrep_cluster_address option for joining a cluster.

A "node" can actually also be used to bootstrap a cluster as the "seed" does described above by placing a flag file in the data volume before boot name /var/lib/mysql/new-cluster.

no-galera

Start server with Galera disabled. Useful for maintenance tasks like performing mysql_upgrade and resetting root credentials.

Reset root password

For example, to reset the root user password, with the Galera container stopped you can run a new temporary container like so:

shell1 $ docker run --rm -v {volume-name}:/var/lib/mysql --name no-galera-temp {image} no-galera --skip-grant-tables
shell2 $ docker exec -it no-galera-temp mysql -u root mysql
MariaDB> update user set password=password("YOUR_NEW_PASSWORD") where user='root' and host='127.0.0.1';
MariaDB> flush privileges;
MariaDB> quit
shell2 $ exit
shell1 $ <CTRL+C>

And now start your Galera container back up with the new root password.

sleep

Start the container but not the server. Runs "sleep infinity". Useful just to get volumes initialized or if you want to docker exec without the server running.

bash

Open a bash shell instead of starting the container. For example bash -c 'touch /var/lib/mysql/new-cluster' to touch the flag file that indicates to start a new cluster on the next startup.

Environment Variables

  • XTRABACKUP_PASSWORD (required unless XTRABACKUP_PASSWORD_FILE is provided)
  • SYSTEM_PASSWORD (required or set to a hash of XTRABACKUP_PASSWORD if provided.)
  • CLUSTER_NAME (optional)
  • NODE_ADDRESS (optional - defaults to ethwe, then eth0)
  • LISTEN_WHEN_HEALTHY (optional) - Specify a port number to open a healthcheck socket on once the cluster has reached a healthy state. Useful with Kontena's wait_for_port feature.
  • HEALTHY_WHILE_BOOTING (optional) - If '1' then the HEALTHCHECK script will report healthy during the boot phase (waiting for DNS to resolve and recovering wsrep position).
  • SKIP_TZINFO (optional) - Specify any value to skip loading of timezone table data when initing a new directory.
  • DEFAULT_TIME_ZONE (optional - defaults to the TZ envvar or to '+00:00' if undefined) - Specify the database's time zone, either in numeric format (+01:00) or in verbal format (CET, Europe/Bratislava, etc.). The latter one is possible only if you haven't specified SKIP_TZINFO. More information about why you would need this is here.
  • SST_METHOD (optional - defaults to 'mariabackup' for 10.2+ and 'xtrabackup-v2' for 10.1) May also be set to 'rsync' or 'mysqldump'. Other methods requiring further configuration or installed dependencies are not available in this image.
  • SKIP_UPGRADES (optional - prevent running run-upgrades.sh script)

Additional variables for "seed":

  • MYSQL_ROOT_PASSWORD (optional) - See also /var/lib/mysql/new-cluster flag file.
  • MYSQL_ROOT_HOST (optional) - Defaults to '127.0.0.1' if not specified. Specify '%' to allow root login from any host.
  • MYSQL_ROOT_SOCKET_AUTH (optional) - Enabled by default, specify 0 to disable. If enabled 'root'@'localhost' is created on bootstrap such that root can login via the unix socket without a password! This allows docker exec commands to work without a password while still requiring a password for login over the network.
  • MYSQL_DATABASE (optional)
  • MYSQL_USER (optional)
  • MYSQL_PASSWORD (optional)

Additional variables for "node":

  • GCOMM_MINIMUM (optional - defaults to 2)

Providing secrets through files

It's also possible to configure the sensitive variables using files, a method used by Docker Swarm, Rancher and perhaps others. The paths to the secret files defaults to /run/secrets/{lower_case_variable_name} but can be specified explicitly as well using the following environment variables:

  • XTRABACKUP_PASSWORD_FILE
  • SYSTEM_PASSWORD_FILE
  • MYSQL_ROOT_PASSWORD_FILE
  • MYSQL_ROOT_HOST_FILE
  • MYSQL_PASSWORD_FILE
  • MYSQL_DATABASE_FILE

Flag Files

In order to accomodate controlling the bootstrapping phase without having to change the CMD which is sometimes hard to do with automated schedulers you can touch the following files to change the bootstrapping behavior before starting the container. All files are expected to be in the /var/lib/mysql directory which you should be mounting as a container volume.

  • /var/lib/mysql/new-cluster - Cause a 'node' container to behave as a 'seed' container on it's first run. This may also be used for recovery in case a Primary Component cannot be formed or for bootstrapping a fresh cluster in place of using the 'seed' container. If the file has any contents they will be used as the MYSQL_ROOT_PASSWORD.
  • /var/lib/mysql/hold-start - Cause a 'node' container to wait until this file is deleted before trying to boot. This could be used in the absence of a scheduler with an easy fine-grained scheduling control.
  • /var/lib/mysql/force-cluster-bootstrapping - Force the creation of MySQL users again ('seed' or 'node' command).
  • /var/lib/mysql/skip-cluster-bootstrapping - Prevent the creation of MySQL users. This file will be created and should not be deleted under normal circumstances.
  • /var/lib/mysql/skip-upgrades - Prevent running the run-upgrades.sh script.

Health Checks

By default there are two HTTP-based healthcheck servers running in the background.

  • Port 8080 only reports healthy when ready to serve clients. (synced)
  • Port 8081 reports healthy as long as the server is synced or donor/desynced state. This one is used to help other nodes determine cluster state before launching the server and also by the Dockerfile HEALTHCHECK command.

The default HEALTHCHECK command also returns healthy status if /var/lib/mysql/sst_in_progress is present to avoid a node being killed during an SST. Otherwise it uses the second health check (port 8081) to return healthy only if it is 'synced' to prevent the node from being killed if it is a donor for a long period of time. How you want the healthcheck command to behave will vary on your uses for the healthcheck so you may need to override it depending on the behavior you desire. Regardless, both healthcheck servers will be started and will use negligible resources unless they are actually being pinged.

Additionally, if a LISTEN_WHEN_HEALTHY port number is specified then the container will start a loop checking it's own port 8080 health check described above until it reports healthy at which point it will open a new socket on this port which just forwards to port 8080. This can be used with Kontena's wait_for_port feature to accomodate the rolling update mechanism.

Upgrading

In general, since MariaDb is not a particularly stable server, often introducing regressions or backwards-compatibility breaks with minor version numbers it is always advised to use specific tags in production and test upgrades on a staging environment first. Also it is advised to read the commit log to see what changes have been made. No warranty is provided, use at your own risk!

Upgrading from 10.1 to 10.2

Before upgrading you need to grant the PROCESS privilege to the xtrabackup user:

mysql> GRANT PROCESS ON *.* TO 'xtrabackup'@'localhost';

Running Tests

The test.sh script is a simple script that starts the seed and node containers using docker run. It starts the seed in the background, outputs the seed logs to the console, then starts a node in the foreground. Success of the test should be determined by inspecting the logs and additional actions like starting additional nodes and killing one or more nodes should be performed to verify that recovery works as expected.

Example

make test-10.11

Or build and run your own image for 10.11 and start a single seed and node:

$ docker build . -f Dockerfile-10.11 -t galera-test-10.11
$ ./test.sh galera-test-10.11

In another console, verify the cluster status and size:

$ docker exec -it cm-galera-test-node1 mysql -be "show status like 'wsrep_cluster_s%';"
+----------------------------+--------------------------------------+
| Variable_name              | Value                                |
+----------------------------+--------------------------------------+
| wsrep_cluster_size         | 3                                    |
| wsrep_cluster_state_uuid   | e54090dc-f892-11ec-ad6f-f2704a681293 |
| wsrep_cluster_status       | Primary                              |
+----------------------------+--------------------------------------+

More Info

  • Tries to handle as many recovery scenarios as possible including full cluster ungraceful shutdown by using --wsrep-recovery and inter-node communication to discover the optimal node for bootstrapping a new cluster when the old one cannot be recovered.
  • If you need to perform manual recovery of a previously healthy cluster you can use "node" mode but touch a file at /var/lib/mysql/new-cluster to force a node to bootstrap a new cluster and bypass the automatic recovery steps.
  • XtraBackup is used for state transfer and MariaDb now supports pc.recovery so the primary component should automatically be recovered in the case of all nodes being gracefully shutdown. It is important tha all nodes are started together so that they can communicate status with each-other.
  • A go server runs within the cluster exposing an http service for intelligent health checking.
    • Port 8080 is used by the Docker 1.12 HEALTHCHECK feature and also can be used by any other health checking node in the network such as HAProxy or Consul to determine readable/writeable nodes.
    • Port 8081 is used to detemine cluster status
  • If your container network uses something other than ethwe* or eth0 then you need to specify NODE_ADDRESS as either the name of the interface to listen on or a grep pattern to match one of the container's IP addresses. E.g.: NODE_ADDRESS='^10.0.1.*'
  • When using DNS for node address discovery the container entrypoint script will wait indefinitely for GCOMM_MINIMUM IP addresses to resolve before trying to start mysqld in case some containers are starting slower than others to increase the chance of a healthy recovery. Scenarios where not enough IPs would resolve might include:
    • Some nodes may finish pulling container images from remote repositories sooner than others
    • Schedulers may not be launching nodes quickly enough
    • Service discovery systems may be slow to propagate updates via DNS
  • If the file /usr/local/lib/startup.sh exists it will be sourced in the start.sh script allowing you to perform initialization tasks if needed.
  • If you need to promote a running node to be a new "Primary Component" you can run the following command to do so:
    • docker exec -i <container> mysql -p /primary-component.sql
  • You can monitor cluster state changes more clearly by setting wsrep_notify_cmd to /usr/local/bin/notify.sh which will output the updates to the Docker logs/console or use your own command to report to your monitoring systems.

Credit