Getting Started with MySQL Orchestrator

Orchestrator is a tool for MySQL HA and replication management.

Getting started

This is a simple set up document to set up an orchestrator.

I just followed these documents at first.

• https://github.com/wagnerjfr/orchestrator-mysql-replication-docker
• https://github.com/openark/orchestrator/blob/master/docs/install.md

Prerequisite

• In order to promote a read replica to a main DB, it looks GTID based replication needs to be enabled.

Build a docker image

At first, build a docker image. I couldn’t find which docker image in DockerHub can be used in a docker-compose.

git clone https://github.com/openark/orchestrator
cd orchestrator
docker build . -t docker/Dockerfile -t orchestrator:latest

Set up an MySQL server for orchestrator

Set up a MySQL server for Orchestrator and create a user and a database.

CREATE DATABASE IF NOT EXISTS orchestrator;
CREATE USER 'orchestrator'@'%' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON `orchestrator`.* TO 'orchestrator'@'%';

Set up an user and permissions on each MySQL server in a MySQL cluster

In each MySQL server of a topology, create an orchestrator user to manage by Orchestrator.

CREATE USER 'orchestrator'@'%' IDENTIFIED BY 'password';
GRANT SUPER, PROCESS, REPLICATION SLAVE, RELOAD ON *.* TO 'orchestrator'@'%';
GRANT SELECT ON mysql.slave_master_info TO 'orchestrator'@'%';

Set up an user for orchestrator

Configure MySQL settings for orchestrator MySQL server and also managed MySQL topology servers in /etc/orchestrator.conf.json.

{
    "MySQLOrchestratorHost": "orchestrator_mysql_db",
    "MySQLOrchestratorPort": 3306,
    "MySQLOrchestratorDatabase": "orchestrator",
    "MySQLOrchestratorUser": "orchestrator",
    "MySQLOrchestratorPassword": "orch_backend_password",

    "MySQLTopologyUser": "orchestrator",
    "MySQLTopologyPassword": "orch_topology_password"
}

Then start the Orchestrator with a few Docker containers. After starting a container, access orchestrator UI by 127.0.0.1:3000

Register a DB cluster into the Orchestrator

On UI, a new DB cluster can be registered. On CLI, we can register it by next.

> docker exec -it cluster_orchestrator_1 orchestrator-client -c discover -i main:3306
main:3306

Use Consul as a KV store

The reason for why a KV store is used and configuration for Consul can be found on the official documents

• Key-Value stores
• Configuration: Key-Value stores

First, update a few fields in orchestrator.conf.json. The details of them can be seen on the above document.

...
    "KVClusterMasterPrefix": "mysql/main",
    "ConsulAddress": "consul-server1:8500",
    "ConsulCrossDataCenterDistribution": true,
...

Note that this configuration assumes that Consul agent isn’t installed an orchestrator instance. Also, I couldn’t figure out how to resolve DNS using consul containers so that we can use Consul DNS name like consul.service..consul, so the traffic isn’t load balanced.

Then, after a cluster is registered on Orchestrator, KVs also are stored in Consul. It can be checked by a consul client.

> docker exec -it cluster_consul-client_1 consul kv export
[
	{
		"key": "mysql/main/main",
		"flags": 0,
		"value": "bWFpbjozMzA2"
	},
	{
		"key": "mysql/main/main/hostname",
		"flags": 0,
		"value": "bWFpbg=="
	},
	{
		"key": "mysql/main/main/ipv4",
		"flags": 0,
		"value": "MTkyLjE2OC4yMDguMg=="
	},
	{
		"key": "mysql/main/main/ipv6",
		"flags": 0,
		"value": ""
	},
	{
		"key": "mysql/main/main/port",
		"flags": 0,
		"value": "MzMwNg=="
	}
]

Support a failover

There is an MySQL configuration about failover. Also, all MySQL servers have to turn on log_slave_updates option.

In order to promote a read replica on Main DB, it seems configuring GTID is required. Maybe Pseudo GTID also works, but haven’t tried. At least it doesn’t work for binary logging based replications.

orchestrator-cli

In order to list up clusters

bash-5.1# orchestrator-client  -c clusters
main:3306

In order to check a topology of each cluster

bash-5.1# orchestrator-client  -c topology -i main:3306
main:3306             [0s,ok,5.7.36-log,rw,ROW,>>]
+ read-replica-1:3306 [0s,ok,5.7.36-log,rw,ROW,>>]
+ read-replica-2:3306 [0s,ok,5.7.36-log,rw,ROW,>>]

To register a cluster

> orchestrator-client -c discover -i main:3306
main:3306

Troubleshootings

Error when a read replica is promoted to a main DB

The example of an error message.

Desginated instance read-replica-2:3306 cannot take over all of its siblings. Error: 2021-11-04 04:34:36 ERROR Relocating 1 replicas of main:3306 below read-replica-2:3306 turns to be too complex; please do it manually

By cli, the same result happened.

bash-5.1# orchestrator-client -c graceful-master-takeover -a main:3306 -d read-replica-1
Desginated instance read-replica-1:3306 cannot take over all of its siblings. Error: 2021-11-04 05:37:45 ERROR Relocating 1 replicas of main:3306 below read-replica-1:3306 turns to be too complex; please do it manually

After GTID replication on MySQL turned on, this error was gone.

I also tried to turn on log_slave_updates on all MySQL servers by following one comment of a GitHub issue, but didn’t solve.

Reference

• docker-compose example

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