To enable HA in a three node cluster:
- Open the configuration/initial/module-shards.conf file on each cluster node.
- Add member-2 and member-3 to the replica list for each data shard.
- Restart all of the nodes. The nodes should automatically sync up with member-1. After some time, the cluster should be ready for operation.
When HA is enabled, you must have at least three replicas of every shard. Each node’s configuration files should look something like this:
module-shards = [
{
name = "default"
shards = [
{
name="default"
replicas = [
"member-1",
"member-2",
"member-3"
]
}
]
},
{
name = "topology"
shards = [
{
name="topology"
replicas = [
"member-1",
"member-2",
"member-3"
]
}
]
},
{
name = "inventory"
shards = [
{
name="inventory"
replicas = [
"member-1",
"member-2",
"member-3"
]
}
]
},
{
name = "toaster"
shards = [
{
name="toaster"
replicas = [
"member-1",
"member-2",
"member-3"
]
}
]
}
]When HA is enabled on multiple nodes, shards will replicate the data for those nodes. Whenever the lead replica on a data shard is brought down, another replica takes its place. As a result, the cluster should remain available. To determine which replica is acting as the lead on a data shard, make an HTTP request to obtain the information for a data shard on any of the nodes. The resulting information will indicate which replica is acting as the lead.
