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mem_broker_replica.md

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Setting Up Backup for Memory Broker

Setting Up Replica for Memory Broker

Build the binaries:

$ cargo build

Run the replica

$ RUST_LOG=warp=info,undermoon=info,mem_broker=info UNDERMOON_ADDRESS=127.0.0.1:8899 UNDERMOON_META_FILENAME=metadata2 target/debug/mem_broker

Run the master Memory

$ RUST_LOG=warp=info,undermoon=info,mem_broker=info UNDERMOON_REPLICA_ADDRESSES=127.0.0.1:8899 UNDERMOON_SYNC_META_INTERVAL=3 target/debug/mem_broker

# Put some data to the master:
$ ./examples/mem-broker/init.sh

# Verify that on master:
curl localhost:7799/api/v3/metadata
...

# Verify tat on replica after 3 seconds:
curl localhost:7799/api/v3/metadata
...
# Replica should have the same data as master.

Note that when master failed, the whole system will NOT automatically fail back to replica. You need to do it by calling the API of coordinator. During this time, the server proxies will still be able to process the requests but the whole system can't scale and failover for server proxies util the Memory Broker endpoint of coordinator is switched to the replica.

Let's say you have already run a coordinator:

$ RUST_LOG=undermoon=info,coordinator=info target/debug/coordinator conf/coordinator.toml

Then you can change master to replica by connecting to coordinator in Redis protocol and changing the config.

# 6699 is the port of coordinators.
$ redis-cli -p 6699 CONFIG SET brokers 127.0.0.1:8899

The newest metadata of the master memory broker has not been replicated to the replica memory broker and fail. We can't recover the lost data but we can bump the metadata epoch by collecting the epoch from all the recorded proxies to recover the service.

So we also need to call this API after reconfiguring the coordinator.

$ curl -XPUT localhost:7799/api/v3/epoch/recovery

Now the system should be able to work again.