Fan-In & All-Masters

dbdeployer supports two multi-source replication topologies where nodes receive writes from more than one master. Both require MySQL 5.7.9 or later.

Fan-In

Fan-in is the inverse of master-slave: multiple masters feed into a single slave. This is useful for consolidating writes from many sources into one replica — for example, aggregating data from multiple application databases.

dbdeployer deploy replication 8.4.8 --topology=fan-in

Default layout: nodes 1 and 2 are masters, node 3 is the slave.

~/sandboxes/fan_in_msb_8_4_8/
├── node1/   # master
├── node2/   # master
├── node3/   # slave (replicates from both masters)
├── check_slaves
├── test_replication
└── use_all

Custom Master and Slave Lists

Use --master-list and --slave-list with --nodes to define any layout:

dbdeployer deploy replication 8.4.8 --topology=fan-in \
    --nodes=5 \
    --master-list="1,2,3" \
    --slave-list="4,5" \
    --concurrent

This creates 5 nodes where nodes 1–3 are masters and nodes 4–5 each replicate from all three masters.

Verifying Fan-In Replication

~/sandboxes/fan_in_msb_8_4_8/test_replication
# master 1
# master 2
# slave 3
# ok - '2' == '2' - Slaves received tables from all masters
# pass: 1
# fail: 0

All-Masters

In the all-masters topology, every node is simultaneously a master and a slave of every other node. This creates a fully-connected circular replication graph where a write on any node propagates to all others.

dbdeployer deploy replication 8.4.8 --topology=all-masters

Default: 3 nodes, each replicating from the other two.

~/sandboxes/all_masters_msb_8_4_8/
├── node1/   # master + slave
├── node2/   # master + slave
├── node3/   # master + slave
├── check_slaves
├── test_replication
└── use_all

Use Cases

Fan-in is suited for:

Data warehouses that consolidate writes from multiple OLTP sources
Centralized audit or logging replicas
Cross-shard aggregation in sharded setups

All-masters is suited for:

Testing multi-source conflict scenarios
Active-active setups where all nodes need to accept writes and stay in sync
Exploring MySQL’s multi-source replication capabilities

Running Queries on All Nodes

~/sandboxes/all_masters_msb_8_4_8/use_all -e "SHOW SLAVE STATUS\G" | grep -E "Master_Host|Running"

Minimum Version

Both topologies require MySQL 5.7.9 or later. Use dbdeployer versions to see what is available.