For a new high-availability deployment, build a MySQL InnoDB Cluster across three separate Linux VPS instances, keep the servers on a private network, use Group Replication for membership and failover, and put MySQL Router in front of the database nodes. A three-member group is the practical minimum because it retains a quorum after one server fails.
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The safest workflow is to install the same supported MySQL release on all nodes, prepare InnoDB and GTID-based replication, use MySQL Shell AdminAPI to create and expand the cluster, then bootstrap Router and point the application at Router rather than at an individual database server. The sections below show the topology, network rules, configuration, commands, failover tests, and recovery procedures.
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MySQL InnoDB Cluster combines four pieces: MySQL Server on each database node, Group Replication for synchronous membership and transaction certification, MySQL Shell for administration, and MySQL Router for application connection routing. The common topology is one read/write primary and two read-only secondaries.
| Component | Role | Where it runs |
|---|---|---|
| MySQL Server | Stores InnoDB data and participates in Group Replication | Every database VPS |
| Group Replication | Replicates committed transactions, tracks membership, and elects a primary when required | Every database VPS |
| MySQL Shell | Runs AdminAPI checks, cluster creation, membership changes, and status commands | An administration host or one secured database host |
| MySQL Router | Discovers cluster metadata and sends client connections to the current primary or read-only members | An application tier or dedicated routing host |
In single-primary mode, only the elected primary accepts writes. The other members keep synchronized copies and can serve read traffic when your application uses a read-only Router endpoint. Group Replication detects a changed membership, but it does not rewrite existing client connections; Router or equivalent middleware is what gives applications a stable endpoint during a primary change.
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Choose the number of VPS nodes from the failure you must survive
Group Replication requires a majority to make progress. MySQL documents the sizing rule as n = 2 × f + 1, where f is the number of involuntary failures the group should tolerate while retaining quorum.
| Members | Failures tolerated with automatic progress | What a further failure means |
|---|---|---|
| 3 | 1 | A second lost member leaves one of three, so automatic progress stops |
| 5 | 2 | A third lost member removes the majority |
| 7 | 3 | A fourth lost member removes the majority |
Three members are therefore the normal minimum for high availability. Put them on separate VPS instances, not three MySQL processes on one machine. Separate failure domains are useful: independent virtual machines, separate host hardware where available, and a private network with predictable latency. If you place members in different regions, measure the resulting latency and bandwidth before production; the official documentation does not define a universal VPS size or latency threshold.
Prepare the Linux VPS layer
Provision separate, reachable instances
- Provision three VPS servers with the same Linux family and a supported, identical MySQL Server release.
- Assign each server a stable private address. Do not use an address that changes when a VPS is restarted.
- Create forward and reverse name resolution for names such as
db1.internal,db2.internal, anddb3.internal. Every member must resolve and reach every other member on the private network. - Keep MySQL data on persistent storage. Select CPU, memory, storage IOPS, and network capacity from measured workload requirements rather than a generic VPS size.
- Install MySQL Shell on a locked-down administration host or on a database host accessible only to administrators.
Open only the required paths
Use host firewalls and, where available, the VPS provider’s private-network firewall. The SQL port and the Group Replication port have different trust boundaries.
| Port | Protocol | Source and purpose |
|---|---|---|
| 3306 | TCP | Application and administration networks to the SQL listener; restrict it to trusted sources |
| 33061 | TCP | Bidirectional Group Replication traffic between all database members; keep it off the public internet |
| Router listener ports | TCP | Application hosts to the Router listeners you configure; do not expose them broadly |
| SSH | TCP | Administration network only, preferably through a bastion or private management path |
Test connectivity from every node, not just from the administration host. A firewall that permits db1 to reach db2 but blocks db3 to reach db1 can produce incorrect membership reporting and failed joins.
getent hosts db1.internal db2.internal db3.internal
nc -vz db1.internal 33061
nc -vz db2.internal 33061
nc -vz db3.internal 33061Prepare MySQL consistently on all members
Use InnoDB and compatible server settings
Store application tables in InnoDB. Other storage engines can cause Group Replication errors or leave tables outside the consistency model you expect. Install the same supported MySQL release on all three VPS servers and keep release compatibility in mind during upgrades.
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Every member needs a unique positive server_id. Enable GTIDs and GTID consistency on every member because Group Replication uses GTIDs to identify committed transactions. Keep lower_case_table_names and default_table_encryption identical across the group. Use row-based replication settings supported by your selected release.
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Core configuration values
AdminAPI should generate release-specific Group Replication details, but each server must have a distinct identity and a distinct internal address. A minimal configuration outline looks like this; substitute the real private names and a single UUID shared by all members.
[mysqld]
server_id=101
gtid_mode=ON
enforce_gtid_consistency=ON
log_bin=binlog
binlog_format=ROW
log_replica_updates=ON
group_replication_group_name='3f4f6f7e-2f5d-4e6e-9f6a-7d5a1f5f7a11'
group_replication_local_address='db1.internal:33061'
group_replication_group_seeds='db1.internal:33061,db2.internal:33061,db3.internal:33061'
group_replication_start_on_boot=ONOn db2 and db3, change server_id and group_replication_local_address; keep the group UUID and seed list consistent. The local address is for Group Replication traffic, not for SQL administration. Do not copy a complete configuration file from one member without changing its identity.
Restart and verify before creating the group
After editing the MySQL configuration, restart each instance during a controlled maintenance window. Verify the effective values from SQL and confirm that the process is listening on the intended interfaces.
mysql -uroot -p -e "SELECT @@server_id, @@gtid_mode, @@enforce_gtid_consistency, @@lower_case_table_names, @@default_table_encryption;"
ss -lntp | grep 3306Also verify that application tables use InnoDB and that no member has unique settings that would make it behave differently. Resolve DNS, firewall, certificate, and authentication problems before attempting a cluster join; fixing them after a partial join is harder to diagnose.
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Create the cluster with MySQL Shell AdminAPI
1. Check the seed instance
Connect MySQL Shell in JavaScript mode to the intended first member. Use an administrative account with the privileges required by AdminAPI, and protect that account with TLS and a strong authentication policy.
mysqlsh --js [email protected]:3306Run the instance validation before creating anything:
dba.checkInstanceConfiguration()Address every reported error. Typical blockers include disabled GTIDs, an incompatible lower-case table setting, a duplicate server ID, non-InnoDB tables, missing binary logging, or a hostname that other members cannot resolve.
2. Let AdminAPI configure supported settings
AdminAPI is intended to avoid hand-editing every Group Replication option. After the check passes, configure the instance and repeat the check on the other two servers.
dba.configureInstance('[email protected]:3306')
dba.configureInstance('[email protected]:3306')
dba.configureInstance('[email protected]:3306')Read the command output and restart a server when AdminAPI requests it. Configuration syntax and required variables can change between MySQL releases, so use the AdminAPI output for the installed release rather than copying an old blog configuration.
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3. Create a single-primary cluster
Connect to db1 again and create the cluster in single-primary mode. This mode is the normal starting point because it limits concurrent write conflicts and gives the application one clear write destination.
var cluster = dba.createCluster('prodCluster', {multiPrimary: false})
cluster.status()The status should show db1 as the primary and an online group. Record the generated cluster name and metadata; Router will use that metadata later.
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Add db2 and db3 through AdminAPI. If the instances contain no required data, AdminAPI can use MySQL Clone to provision a joining member. If they already contain data, follow the compatibility and provisioning checks reported by AdminAPI rather than attempting an ad hoc copy.
cluster.addInstance('[email protected]:3306')
cluster.addInstance('[email protected]:3306')
cluster.status()Wait for each member to become ONLINE. Confirm that exactly one member is PRIMARY and that the other members are secondary/read-only members in the intended mode. Do not direct production traffic to a member that is still joining or recovering.
Single-primary and multi-primary are different operating models
| Decision point | Single-primary | Multi-primary |
|---|---|---|
| Write conflicts | Concentrated on one primary, so conflict handling is simpler | Concurrent writes can conflict across members and require application-aware design |
| Failover | Elects a replacement primary when the current one is lost | Several members can accept writes, but conflict and certification failures are more visible |
| Application complexity | One write endpoint through Router | Applications must understand multi-writer behavior and retry conflicts correctly |
| Read scaling | Reads can use secondary Router destinations | Reads and writes can be distributed, subject to conflict and consistency trade-offs |
| Operational burden | Lower for a first deployment | Higher; choose it only with a documented workload reason |
Bootstrap MySQL Router for application failover
Router must be bootstrapped against the cluster metadata. Run it on an application tier or a dedicated routing host, not on an internet-facing address.
mysqlrouter --bootstrap [email protected]:3306
--directory /etc/mysqlrouter
--user mysqlrouterUse the generated Router configuration as the application-facing endpoint. It contains listeners for read/write and, when enabled, read-only traffic. Keep direct db1, db2, and db3 addresses for administration and emergency recovery only.
Change the application’s connection string to the Router hostname and listener port. Test both a normal connection and a transaction that fails over. Router refreshes cluster metadata and routes new connections to the current primary; existing TCP sessions still need the application’s connection pool and retry policy to reconnect.
Protect Router and member traffic with TLS
Use TLS for client connections, recovery operations, and member traffic where supported by your deployment policy. Router supports TLS verification modes including VERIFY_CA and VERIFY_IDENTITY. With identity verification, certificate names must match the hostnames applications actually use. A certificate valid for db1.internal but a connection string that uses an unrelated alias will fail verification.
Store private keys with filesystem permissions that allow only the Router or MySQL service account to read them. Monitor certificate expiration and test certificate rotation before an emergency failover.
Validate quorum, routing, and failover before production
Check normal health
- Run
cluster.status()and confirm every intended member isONLINE. - Confirm one primary in single-primary mode and verify that secondaries are not accepting unintended writes.
- Check Group Replication membership, applier state, transaction backlog, disk space, memory pressure, and error logs.
- Open an application connection through Router and verify that writes land on the primary and reads use the endpoint your design specifies.
- Confirm that backups complete independently of replication. A replicated deletion is still a deletion on every member.
Exercise an unplanned primary loss
- Use a maintenance or test window and stop the primary MySQL service or isolate its private network interface.
- Watch
cluster.status()until the remaining members agree on membership and a new primary is elected. - Open a new application connection through Router and verify that it reaches the elected primary.
- Check the application’s connection-pool logs. Existing sessions may fail; the application must reconnect and retry only transactions that are safe to retry.
- Restore the failed VPS, inspect its logs, and rejoin it only after its data and configuration pass AdminAPI validation.
Exercise a planned switchover
Use the cluster’s supported primary-switching operation from MySQL Shell for a planned maintenance event rather than abruptly stopping the primary. Drain application traffic, perform the switchover, confirm Router metadata refresh, and then patch or reboot the former primary.
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Recovery procedures and routine operations
Rejoining a rebuilt VPS
Treat a rebuilt server as a new instance. Install the same MySQL release, restore consistent configuration values, assign a unique server ID and local Group Replication address, and verify DNS and firewall access. Run dba.checkInstanceConfiguration() before adding it. Allow AdminAPI to clone or otherwise synchronize the member according to the state it reports; do not attach a stale data directory by hand.
When the group loses quorum
If enough members disappear that no majority remains, automatic progress stops by design. Do not force multiple isolated nodes to accept writes. First determine which member has the authoritative, most recent state, restore private-network connectivity or recover failed VPS instances, and follow the MySQL release’s documented rebootstrap procedure. Record the event and investigate why quorum was lost before returning to production traffic.
Monitor the parts that can fail independently
- Group membership and quorum.
- Primary and secondary state, applier errors, and transaction backlog.
- CPU, memory, disk capacity, storage latency, and network saturation on every VPS.
- Router metadata refresh, listener availability, and connection errors.
- TLS certificate expiry and hostname mismatches.
- Private-network reachability and DNS consistency.
- Backup success, restore duration, and the age of the newest restorable copy.
Plan upgrades as a runbook
Keep MySQL versions compatible during a rolling upgrade and follow the release-specific Group Replication and Router compatibility guidance. Upgrade one secondary, validate that it returns to ONLINE, perform a controlled primary switchover if required, and then upgrade the former primary. Never assume that a package upgrade preserves every configuration variable; rerun AdminAPI checks after each change.
Quick Recap
Troubleshoot the common failure modes
| Symptom | Likely cause | Action |
|---|---|---|
| AdminAPI refuses an instance | GTID, server ID, storage engine, version, or naming inconsistency | Run dba.checkInstanceConfiguration(), fix every reported item, restart if requested, and check again |
| Member never becomes ONLINE | Blocked 33061/TCP, incorrect local address, DNS failure, or certificate/authentication problem | Test bidirectional reachability from all members and compare the effective Group Replication addresses |
| Group has no primary | Loss of quorum or an election that cannot complete | Restore enough members and private connectivity; do not create parallel writable groups |
| Application keeps writing to a failed node | Connection string points directly to a VPS or the pool has stale sessions | Use Router for new connections, close failed sessions, and enable safe reconnect logic |
| TLS verification fails after routing changes | Certificate names do not match the hostname used by the application or Router | Use matching DNS names and certificate identities, then retest with strict verification |
| New member has unexpected data | It was added with an incompatible or stale data directory | Remove it from service, follow the AdminAPI provisioning path, and rejoin only after validation |
Production readiness checklist
- Three separate VPS instances are provisioned on a stable private network.
- Every member has a unique positive
server_id, a unique Group Replication local address, and the same group UUID. - Application tables use InnoDB; GTID mode and GTID consistency are enabled everywhere.
- MySQL release compatibility, lower-case table behavior, encryption defaults, and row-based replication settings are consistent.
- TCP 3306 is restricted to trusted application and administration sources; TCP 33061 is reachable only between members.
- AdminAPI reports clean instance configuration, and all intended members show
ONLINE. - Router is bootstrapped, protected with TLS, and used by the application instead of direct node addresses.
- Connection pools handle dropped sessions and retry only transactions that your application can safely retry.
- Planned switchover, unplanned primary loss, quorum loss, and rebuilt-member rejoin have been tested and documented.
- Backups have been restored in a separate test, and monitoring covers membership, replication health, Router, certificates, resources, and network reachability.
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