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Configure MySQL Group Replication by giving every server a unique identity, compatible binary-log and GTID settings, and reachable Group Replication addresses; bootstrap exactly one seed member; join the remaining members through the recovery seed; and verify that each member is ONLINE. Group Replication maintains membership and detects failures, but client failover still requires MySQL Router, a connector, a load balancer, or equivalent middleware.
What the finished deployment looks like
A Group Replication deployment is a group of MySQL servers that exchange membership and transaction information over a dedicated peer-to-peer communication channel. One server starts the group, and other servers join that existing group through the configured seed and distributed-recovery path.
Every member must agree on the group identity and on settings that affect replication. Each must also be reachable on its Group Replication address. The SQL address used by applications can be separate from the internal Group Replication address, which is useful when firewalls or security policy require client and replication traffic to be segmented.
The documented maximum is nine servers in one group. A larger fleet must be divided into separate groups or designed around another replication topology; adding a tenth member is not a supported way to scale this group.
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Before changing configuration, decide whether applications need one writer or several. Single-primary mode elects one read-write primary and keeps other members read-only for normal application writes. Multi-primary mode permits writes on multiple members, but conflict handling and workload placement become application and operations concerns.
Prerequisites and a topology plan
Use compatible MySQL releases
Install the Group Replication plugin on every instance, or confirm that the package already includes it. Replication variables, account privileges, recovery behavior, and available status columns can differ between MySQL releases, so use the manual for the exact release installed on each server. Keep versions compatible during normal operation and follow the release-specific upgrade procedure when versions must be mixed temporarily.
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SELECT PLUGIN_NAME, PLUGIN_STATUS, PLUGIN_TYPE
FROM INFORMATION_SCHEMA.PLUGINS
WHERE PLUGIN_NAME = 'group_replication';The result should show the Group Replication plugin in an enabled state. If it is missing or disabled, install or enable it according to the package and release documentation before continuing.
Assign identities and addresses
Each instance needs a unique server_id and a unique server UUID. Do not clone a data directory or configuration and leave the source identity unchanged. A duplicated identity can prevent a member from joining or make monitoring ambiguous.
Give every server a distinct group_replication_local_address. For example, a three-member lab might use db-a.example.net:33061, db-b.example.net:33061, and db-c.example.net:33061. These addresses are examples; choose ports permitted by your network policy.
Use fully qualified hostnames only when every member can resolve them consistently. Otherwise use reachable IP addresses. Test name resolution and TCP connectivity in both directions between all members, not only from the first server to the others.
Open and segment the required traffic
Permit bidirectional TCP traffic on the Group Replication port between members. Permit the SQL port from application networks and administration networks as required. If internal replication traffic must not be exposed to client networks, place the Group Replication addresses on a separate interface or firewall zone and advertise the SQL addresses only to clients.
A successful ping is not sufficient proof: Group Replication needs the configured TCP port, and a firewall can allow ICMP while blocking that port. Test the actual port from each member to every other member before starting the group.
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Align replication settings
Enable binary logging and configure the GTID and replication settings required by your MySQL release and chosen Group Replication mode. The exact list is release-dependent; verify it against the manual for that release instead of copying settings from a different major version.
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Settings that must be consistent across members should be identical. Oracle’s variable reference notes that some Group Replication variables cannot be changed while Group Replication is running. Changing one of those values requires a controlled stop of the group and a full reboot or new bootstrap before the value takes effect.
Record the intended values in configuration management, but do not persist the bootstrap switch described below. It is a run-time control for creating the first group, not a permanent server setting.
Create the distributed-recovery account
Joining members use a dedicated account to copy missing transactions from a donor through the group_replication_recovery channel. Create that account on the seed, and make the same credential available to joining members using the method supported by your release.
The required privileges have changed across MySQL versions. Apply the privilege set documented for the installed release rather than assuming that an account copied from an older tutorial is sufficient. Restrict the account’s host pattern to the replication network where practical, protect its password, and use TLS for recovery if your security policy requires encrypted replication traffic.
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IDENTIFIED BY 'Use-a-long-random-secret-before-production';The password above is an example value, not a production credential. Supply credentials either when starting Group Replication or through the configured recovery channel. Passing them at start time can avoid storing them in a static option file; configuring the channel can support automatic starts, but it requires careful protection of the stored secret.
Confirm that the account can authenticate from every member’s recovery address before you attempt a join. An account that works from the seed but is blocked from a joining host will leave that member in recovery or an error state.
Configure and bootstrap the first member
Set the group identity and seed values
Choose one group name and use it on every member. A UUID-form group name is customary. Configure the seed list with the local addresses that new members may contact. The first server’s local address must be included in the addresses other members can reach.
Configure the seed’s server identity, binary logging, GTID settings, local address, group name, recovery channel, and any mode-specific options before starting replication. Do not enable bootstrap in a persistent option file.
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Run the bootstrap sequence once
On the one server that will create the group, execute these statements in this order:
SET GLOBAL group_replication_bootstrap_group = ON;
START GROUP_REPLICATION;
SET GLOBAL group_replication_bootstrap_group = OFF;The first statement permits this server to create the initial group. The second starts Group Replication. The third immediately disables the permission so a later restart cannot accidentally create another independent group.
“The bootstrap should only be done by a single server, the one that starts the group and only once.” — Oracle MySQL Reference Manual, Bootstrapping the Group
Never leave group_replication_bootstrap_group=ON in an option file. If it remains enabled and the server restarts, it can bootstrap a second group instead of rejoining the existing one. That creates a serious split in membership and transaction history.
Check that the seed is really online
Do not proceed merely because START GROUP_REPLICATION returned without an immediate error. Query the membership table and confirm the member state, address, port, role, and group communication details.
SELECT *
FROM performance_schema.replication_group_members;The seed should appear with MEMBER_STATE equal to ONLINE. Check that its host and port are the values you intended and that the group name and communication stack are correct. If the table is empty or the state is not ONLINE, stop and correct the seed before adding other servers.
Join each additional server
Prepare the joining instance
Repeat the preparation process on every additional server: install or verify the plugin, assign a unique server identity, enable the required logging and GTID settings, configure the same group name, set a unique local communication address, and provide the seed list and recovery credentials.
Do not set group_replication_bootstrap_group to ON on a joining member. It must contact the existing group instead of attempting to create a new one.
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Make sure the joining member’s SQL and Group Replication ports are reachable from the seed and from the other members. Verify that the recovery account can authenticate from the joining host.
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Start Group Replication and allow recovery
Start Group Replication on the joining server, supplying the recovery account at start time if that is your chosen credential method:
START GROUP_REPLICATION
USER = 'gr_recovery',
PASSWORD = 'Use-the-protected-production-secret';If your release and security design use a preconfigured recovery channel, start the service without exposing the secret in the command history. The joining member first obtains current group membership information, then selects a donor and copies the transactions it lacks through distributed recovery.
Recovery duration depends on the amount of missing data, donor capacity, network throughput, and disk performance. Do not direct application traffic to a member while it is still recovering. Wait until the membership table reports ONLINE.
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Run the membership query on an existing member and on the new member. Confirm that every expected server appears exactly once and that each has the expected host, port, version, role, and communication details.
SELECT MEMBER_ID,
MEMBER_HOST,
MEMBER_PORT,
MEMBER_STATE,
MEMBER_ROLE,
MEMBER_VERSION,
MEMBER_COMMUNICATION_STACK
FROM performance_schema.replication_group_members;Column availability can vary by MySQL release. If a selected column is unavailable, use SELECT * and inspect the columns exposed by that release. A member is ready for application traffic only after its state is ONLINE and its role matches the routing policy you intend to use.
Choose single-primary or multi-primary mode
| Decision area | Single-primary | Multi-primary |
|---|---|---|
| Writer topology | One elected primary accepts normal writes; other members serve reads according to policy. | Multiple members can accept writes. |
| Conflict risk | Lower application conflict risk because writes converge through one writer. | Higher risk of certification conflicts and workload collisions; design keys and transactions carefully. |
| Application behavior | Suits applications that expect one writable endpoint. | Requires applications to understand multiple writable members and possible transaction retries. |
| Failure behavior | The group can elect another primary when the current one fails, but clients still need a new connection route. | Another writable member may already exist, but clients still need routing and failed-session recovery. |
| Operational complexity | Simpler write ownership and troubleshooting. | More demanding conflict analysis, schema design, and workload placement. |
| Client routing | Route writes to the current primary and reads according to your consistency needs. | Route to an allowed writable member and handle conflicts or retries. |
Select the mode before production deployment and test the behavior of your connectors and transactions in that mode. Group membership and failure detection are provided by Group Replication, but application semantics remain your responsibility.
Configure client failover separately
Group Replication does not move existing client sessions when a member fails. A TCP connection that was established to the failed server must be closed and re-established by the client or by an intermediary.
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- MySQL Router: route new connections to the current primary or to eligible read-only members, according to the deployment mode.
- Connector-aware routing: configure a MySQL connector’s failover or multi-host behavior and ensure the application retries only transactions that are safe to retry.
- Load balancer: perform health checks that distinguish an
ONLINEand eligible member from a server that is merely accepting TCP connections. - Equivalent middleware: use a service-discovery or proxy layer that understands member role and removes failed endpoints.
Test both new-connection routing and in-flight transaction behavior. A failover system that reconnects successfully can still duplicate a non-idempotent operation if the application retries without knowing whether the original transaction committed.
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Make the membership table part of routine monitoring. Alert on a member leaving ONLINE, on an unexpected role change, on a version mismatch, and on a communication address that differs from the approved topology.
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Use the Group Replication Performance Schema tables and status variables provided by your installed release to inspect distributed recovery, donor selection, certification, and communication health. Monitor the recovery channel separately from ordinary SQL traffic so that a stalled join is visible before an operator routes clients to it.
Keep an inventory containing each member’s server identity, SQL address, Group Replication address, MySQL version, configured role, and firewall path. This makes duplicate identities and stale seed lists easier to detect during maintenance.
Troubleshoot members that are not ONLINE
The member does not appear in the group
- Confirm that the joining server uses the exact group name and a unique server identity.
- Resolve every hostname from every member; do not test resolution only on the seed.
- Test TCP connectivity to each configured seed and to the member’s advertised local address.
- Check that the joining member’s local address is not duplicated by another server.
- Verify that the Group Replication plugin is installed and enabled.
The state is OFFLINE or ERROR
Inspect the MySQL error log and compare the joining server’s replication and GTID settings with the seed. Common causes include an incompatible release-specific setting, binary logging or GTID configuration that does not meet the requirements for that release, a duplicate UUID, or an inability to authenticate with the recovery account.
Correct the configuration while Group Replication is stopped, then start it again. Do not repeatedly toggle bootstrap as a troubleshooting shortcut; only the original seed should use the bootstrap sequence.
The state remains RECOVERING
A recovering member has joined the group but has not finished copying missing transactions. Check the recovery-channel status and the Group Replication recovery tables for authentication failures, donor availability, network interruptions, or a growing transaction backlog. Ensure at least one suitable donor remains ONLINE and that disk space and I/O capacity are sufficient.
Keep the member out of application rotation until recovery completes. If recovery repeatedly fails, stop the member, correct the underlying account or network problem, and restart recovery rather than bootstrapping a new group.
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Inspect all option files and startup automation for a persistent group_replication_bootstrap_group=ON. Remove it, stop the unintended group safely, and follow the documented recovery procedure for rejoining the intended group. The bootstrap flag is designed for a controlled run-time operation and should be disabled immediately after the first member starts.
Maintenance, failover, and planned changes
Before planned maintenance, confirm that enough members will remain available for the intended operating mode and that client middleware can route around the server being stopped. Drain or redirect application traffic first, then stop Group Replication or the MySQL instance according to your maintenance procedure.
After maintenance, verify the member’s version, identity, addresses, role, and ONLINE state before returning it to rotation. Check distributed recovery if the server was offline long enough to miss transactions.
When changing a Group Replication variable that requires consistency, plan a coordinated group stop and full reboot or bootstrap. A change made on only one running member may be rejected or may leave the group operating with an unintended configuration.
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Rehearse the complete recovery path during a maintenance window: loss of the primary, client reconnection, member rejoin, donor recovery, and restoration of the failed server. Testing reveals whether firewall rules, credentials, health checks, and application retry logic work together rather than merely proving that replication starts.
Deployment checklist
- Every member has a unique
server_idand server UUID. - The Group Replication plugin is installed and enabled on every instance.
- Binary logging, GTID, and other required settings match the installed MySQL release and selected mode.
- Every member has a unique, reachable
group_replication_local_address. - Hostnames resolve consistently, or reachable IP addresses are used.
- Member-to-member Group Replication TCP traffic is allowed in both directions.
- The dedicated recovery account has the privileges required by the installed release and is protected appropriately.
- The group name and compatible settings are identical across members.
- Only the first server used
group_replication_bootstrap_group=ON, and it was turned off immediately. - The seed reports
ONLINEbefore any join is attempted. - Each joining member reaches
ONLINEbefore application traffic is sent to it. - Client routing and reconnection are provided by Router, a connector, a load balancer, or equivalent middleware.
- The design contains no more than nine servers in the group.
- Bootstrap, recovery, and client failover have been tested during planned maintenance.
Key operational boundary
Group Replication solves coordinated membership, transaction certification, and failure detection among up to nine MySQL servers. It does not by itself provide a client endpoint, move existing sessions, or decide how an application should handle transaction retries. A reliable deployment therefore treats server configuration, recovery credentials, observability, and client routing as separate pieces that must all be verified before production traffic is enabled.
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