Overview

This demo showcases Confluent Platform's Multi-Region Replication capability built directly into Confluent Server starting with release 5.4.

For more information:

Blog post: Built-In Multi-Region Replication with Confluent Platform 5.4-preview
Confluent Platform documentation

NOTE: There is a different demo for a multi-datacenter design with two instances of Confluent Replicator copying data bidirectionally between the datacenters.

Multi-region Architecture

This demo has the following architecture. There are three regions west, central, and east. The naming convention of the brokers are broker-[region]-[broker_id].

Configurations

The full broker configurations are in the docker-compose.yml file. Here are some relevant configuration parameters that are used by Multi-Region Replication.

Broker

broker.rack: identifies the location of the broker. For the demo, it represents a region, either east or west
replica.selector.class=org.apache.kafka.common.replica.RackAwareReplicaSelector: allows clients to read from followers (in contrast, clients are typically only allowed to read from leaders)

Client

client.rack: identifies the location of the client. For the demo, it represents a region, either east or west

Topic

--replica-placement <path-to-replica-placement-policy-json>: at topic creation, this defines the replica placement policy for a given topic

Concepts

Replicas are brokers assigned to a topic-partition, and they can be a Leader, Follower, or Observer. A Leader is the broker/replica accepting produce messages. A Follower is a broker/replica that can join an ISR list and participate in the calculation of the high watermark (used by the leader when acknowledging messages back to the producer).

An ISR list (in-sync replicas) includes brokers that have a given topic-partition. The data is copied from the leader to every member of the ISR before the producer gets an acknowledgement. The followers in an ISR can become the leader if the current leader fails.

An Observer is a broker/replica that also has a copy of data for a given topic-partition, and consumers are allowed to read from them even though it is not the leader (known as "Follower Fetching"). However, the data is copied asynchronously from the leader such that a producer does not wait on observers to get back an acknowledgement. By default, observers do not participate in the ISR list and cannot automatically become the leader if the current leader fails, but if a user manually changes leader assignment then they can participate in the ISR list.

Run the Demo

Install the demo

Clone the confluentinc/examples GitHub repo and go to the folder with the Multi-Region Replication demo:

git clone https://github.com/confluentinc/examples
cd examples/multiregion

Start Docker Compose

Run the following command.

docker-compose up -d

You should see the following Docker containers with docker-compose ps:

      Name                   Command            State                            Ports                          
----------------------------------------------------------------------------------------------------------------
broker-east-3       /etc/confluent/docker/run   Up      0.0.0.0:8093->8093/tcp, 9092/tcp, 0.0.0.0:9093->9093/tcp
broker-east-4       /etc/confluent/docker/run   Up      0.0.0.0:8094->8094/tcp, 9092/tcp, 0.0.0.0:9094->9094/tcp
broker-west-1       /etc/confluent/docker/run   Up      0.0.0.0:8091->8091/tcp, 0.0.0.0:9091->9091/tcp, 9092/tcp
broker-west-2       /etc/confluent/docker/run   Up      0.0.0.0:8092->8092/tcp, 0.0.0.0:9092->9092/tcp          
zookeeper-central   /etc/confluent/docker/run   Up      2181/tcp, 0.0.0.0:2182->2182/tcp, 2888/tcp, 3888/tcp    
zookeeper-east      /etc/confluent/docker/run   Up      2181/tcp, 0.0.0.0:2183->2183/tcp, 2888/tcp, 3888/tcp    
zookeeper-west      /etc/confluent/docker/run   Up      0.0.0.0:2181->2181/tcp, 2888/tcp, 3888/tcp

Inject latency and packet loss

This demo injects latency between the regions and packet loss to simulate the WAN link. It uses Pumba.

Run the Dockerized Pumba scripts:

./scripts/latency_docker.sh

You should see the following Docker containers with docker container ls --filter "name=pumba":

CONTAINER ID        IMAGE                 COMMAND                  CREATED             STATUS              PORTS               NAMES
652fcf244c4d        gaiaadm/pumba:0.6.4   "/pumba netem --dura…"   9 seconds ago       Up 8 seconds                            pumba-loss-east-west
5590c230aef1        gaiaadm/pumba:0.6.4   "/pumba netem --dura…"   9 seconds ago       Up 8 seconds                            pumba-loss-west-east
e60c3a0210e7        gaiaadm/pumba:0.6.4   "/pumba netem --dura…"   9 seconds ago       Up 8 seconds                            pumba-high-latency-west-east
d3c1faf97ba5        gaiaadm/pumba:0.6.4   "/pumba netem --dura…"   9 seconds ago       Up 8 seconds                            pumba-medium-latency-central

View IP addresses in the demo:

docker inspect -f '{{.Name}} - {{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' $(docker ps -aq)

Create Topics

Create three Kafka topics by running the following script.

./scripts/create-topics.sh

The script creates each topic with a different replica placement policy that specifies a set of matching constraints, i.e., count and rack for replicas and observers. The replica placement policy file is defined with the argument --replica-placement <path-to-replica-placement-policy-json> mentioned earlier (these files are in the config directory). Each placement also has a minimum count associated with it that allows users to guarantee a certain spread of replicas throughout the cluster.

Topic name	Leader	Followers (sync replicas)	Observers (async replicas)	ISR list
single-region	1x west	1x west	n/a	{1,2}
multi-region-sync	1x west	1x west, 2x east	n/a	{1,2,3,4}
multi-region-async	1x west	1x west	2x east	{1,2}

The playbook below highlights client performance differences between these topics depending on the relative location of clients and brokers.

Verify topic replica placement:

./scripts/describe-topics.sh

Sample output:

==> Describe topic single-region

Topic: single-region	PartitionCount: 1	ReplicationFactor: 2	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[]}
	Topic: single-region	Partition: 0	Leader: 2	Replicas: 2,1	Isr: 2,1	Offline: 

==> Describe topic multi-region-sync

Topic: multi-region-sync	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}},{"count":2,"constraints":{"rack":"east"}}],"observers":[]}
	Topic: multi-region-sync	Partition: 0	Leader: 1	Replicas: 1,2,3,4	Isr: 1,2,3,4	Offline: 

==> Describe topic multi-region-async

Topic: multi-region-async	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[{"count":2,"constraints":{"rack":"east"}}]}
	Topic: multi-region-async	Partition: 0	Leader: 2	Replicas: 2,1,3,4	Isr: 2,1	Offline: 	Observers: 3,4

Observations:

Topic multi-region-async has replicas across west and east regions, but only 1 and 2 are in the ISR, and 3 and 4 are observers.

Producer Testing

This section tests the differences in replication policies on producers. Run the producer perf test:

./scripts/run-producer.sh

Sample output:

==> Produce: Single-region Replication (topic: single-region) 
5000 records sent, 240.453977 records/sec (1.15 MB/sec), 10766.48 ms avg latency, 17045.00 ms max latency, 11668 ms 50th, 16596 ms 95th, 16941 ms 99th, 17036 ms 99.9th.

==> Produce: Multi-region Sync Replication (topic: multi-region-sync) 
100 records sent, 2.145923 records/sec (0.01 MB/sec), 34018.18 ms avg latency, 45705.00 ms max latency, 34772 ms 50th, 44815 ms 95th, 45705 ms 99th, 45705 ms 99.9th.

==> Produce: Multi-region Async Replication to Observers (topic: multi-region-async) 
5000 records sent, 228.258388 records/sec (1.09 MB/sec), 11296.69 ms avg latency, 18325.00 ms max latency, 11866 ms 50th, 17937 ms 95th, 18238 ms 99th, 18316 ms 99.9th.

Observations:

In the first and third cases, topics single-region and multi-region-async have nearly the same throughput performance (e.g., 1.15 MB/sec and 1.09 MB/sec, respectively, in the above example), because only the replicas in the west region need to ack.
In the second case for topic multi-region-sync, due to the poor network bandwidth between the east and west regions and due to an ISR made up of brokers in both regions, it took a big throughput hit (e.g., 0.01 MB/sec in the above example). This is because the producer is waiting for an ack from all members of the ISR before continuing, including those in west and east.
The observers in the third case for topic multi-region-async didn't affect the overall producer throughput because the west region is sending an ack back to the producer after it has been replicated twice in the west region, and it is not waiting for the async copy to the east region.

Consumer Testing

This section tests the differences in follower fetching in the consumers. Run the consumer perf test where the consumer is in east:

./scripts/run-consumer.sh

Sample output:

==> Consume from east: Multi-region Async Replication reading from Leader in west (topic: multi-region-async)

start.time, end.time, data.consumed.in.MB, MB.sec, data.consumed.in.nMsg, nMsg.sec, rebalance.time.ms, fetch.time.ms, fetch.MB.sec, fetch.nMsg.sec
2019-09-25 17:10:27:266, 2019-09-25 17:10:53:683, 23.8419, 0.9025, 5000, 189.2721, 1569431435702, -1569431409285, -0.0000, -0.0000


==> Consume from east: Multi-region Async Replication reading from Observer in east (topic: multi-region-async)

start.time, end.time, data.consumed.in.MB, MB.sec, data.consumed.in.nMsg, nMsg.sec, rebalance.time.ms, fetch.time.ms, fetch.MB.sec, fetch.nMsg.sec
2019-09-25 17:10:56:844, 2019-09-25 17:11:02:902, 23.8419, 3.9356, 5000, 825.3549, 1569431461383, -1569431455325, -0.0000, -0.0000

Observations:

In the first case, the consumer running in east reads from the leader in west, and so it is negatively impacted by the low bandwidth between east and west. Its throughput is lower (e.g. 0.9025 MB.sec in the above example).
In the second case, the consumer running in east reads from the follower that is also in east. Its throughput is higher (e.g. 3.9356 MB.sec in the above example).

Monitoring Observers

Notice that the multi-region-async topic has a JMX metric ReplicasCount that includes observers, whereas InSyncReplicasCount excludes observers. The new JMX metric CaughtUpReplicasCount (kafka.cluster:type=Partition,name=CaughtUpReplicasCount,topic=([-.\w]+),partition=([0-9]+)) across all brokers in the cluster reflects whether all the replicas, including observers, are caught up with the leader such that their log end offset is at least at the high watermark.

./scripts/jmx_metrics.sh

Sample output:

==> Monitor ReplicasCount

single-region: 2
multi-region-sync: 4
multi-region-async: 4


==> Monitor InSyncReplicasCount

single-region: 2
multi-region-sync: 4
multi-region-async: 2


==> Monitor CaughtUpReplicasCount

single-region: 2
multi-region-sync: 4
multi-region-async: 4

Failover and Failback

Fail region west

docker-compose stop broker-west-1 broker-west-2 zookeeper-west

Verify the new topic replica placement:

./scripts/describe-topics.sh

Sample output:

==> Describe topic single-region

Topic: single-region	PartitionCount: 1	ReplicationFactor: 2	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[]}
	Topic: single-region	Partition: 0	Leader: none	Replicas: 2,1	Isr: 1	Offline: 2,1

==> Describe topic multi-region-sync

Topic: multi-region-sync	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}},{"count":2,"constraints":{"rack":"east"}}],"observers":[]}
	Topic: multi-region-sync	Partition: 0	Leader: 3	Replicas: 1,2,3,4	Isr: 3,4	Offline: 1,2

==> Describe topic multi-region-async

Topic: multi-region-async	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[{"count":2,"constraints":{"rack":"east"}}]}
	Topic: multi-region-async	Partition: 0	Leader: none	Replicas: 2,1,3,4	Isr: 1	Offline: 2,1	Observers: 3,4

Observations:

In the first case, the topic single-region has no leader, because it had only two replicas in the ISR, both of which were in the west region and are now down.
In the second case, the topic multi-region-sync automatically elected a new leader in east (e.g. replica 3 in the above output). Clients can failover to those replicas in the east region.
In the third case, the topic multi-region-async also has no leader, because it had only two replicas in the ISR, both of which were both in the west region and are now down. The observers in the east region are not eligible to become leaders automatically because they were not in the ISR.

Fail over observers

To explicitly fail over the observers in the topic multi-region-async to the east region, trigger leader election (note that unclean leader election may result in data loss):

docker-compose exec broker-east-4 kafka-leader-election --bootstrap-server broker-east-4:19094 --election-type UNCLEAN --topic multi-region-async --partition 0

Describe the topics again.

./scripts/describe-topics.sh

Sample output:

...
==> Describe topic multi-region-async

Topic: multi-region-async	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[{"count":2,"constraints":{"rack":"east"}}]}
	Topic: multi-region-async	Partition: 0	Leader: 3	Replicas: 2,1,3,4	Isr: 3,4	Offline: 2,1	Observers: 3,4
...

Observations for topic multi-region-async:

It has a leader again (e.g. replica 3 in the above output)
The observers are now in the ISR list (e.g. replicas 3,4 in the above output)

Failback region west

docker-compose start broker-west-1 broker-west-2 zookeeper-west

Wait for 5 minutes, which is the default duration for leader.imbalance.check.interval.seconds, until the leadership election restores the preferred replicas. (You can also trigger it with docker-compose exec broker-east-4 kafka-leader-election --bootstrap-server broker-east-4:19094 --election-type PREFERRED --all-topic-partitions).

Verify the new topic replica placement is restored.

./scripts/describe-topics.sh

Sample output:

Topic: single-region	PartitionCount: 1	ReplicationFactor: 2	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[]}
	Topic: single-region	Partition: 0	Leader: 2	Replicas: 2,1	Isr: 1,2	Offline: 

==> Describe topic multi-region-sync

Topic: multi-region-sync	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}},{"count":2,"constraints":{"rack":"east"}}],"observers":[]}
	Topic: multi-region-sync	Partition: 0	Leader: 1	Replicas: 1,2,3,4	Isr: 3,4,2,1	Offline: 

==> Describe topic multi-region-async

Topic: multi-region-async	PartitionCount: 1	ReplicationFactor: 4	Configs: min.insync.replicas=1,confluent.placement.constraints={"version":1,"replicas":[{"count":2,"constraints":{"rack":"west"}}],"observers":[{"count":2,"constraints":{"rack":"east"}}]}
	Topic: multi-region-async	Partition: 0	Leader: 2	Replicas: 2,1,3,4	Isr: 2,1	Offline: 	Observers: 3,4

Observations:

All topics have leaders again, in particular single-region which lost its leader when the west region failed
The leaders are restored to the east region. If they are not, then wait a full 5 minutes (duration of leader.imbalance.check.interval.seconds)

Note: On failback from a failover to observers, any data that was not replicated to observers will be lost because logs are truncated before catching up and joining the ISR.

Run end-to-end demo

All the individual steps above can be run with this automated script:

./scripts/start.sh

Stop demo

Stop the demo and all Docker containers.

./scripts/stop.sh

Troubleshooting

If containers fail to ping each other (e.g., failures seen in running ./scripts/validate_connectivity.sh), then stop the demo, clean up the Docker environment, and restart the demo. If it still fails, restart Docker and run again.

# Stop demo
./scripts/stop.sh

# Clean up the Docker environment
for c in $(docker container ls -q --filter "name=pumba"); do docker container stop "$c" && docker container rm "$c"; done
docker-compose down -v --remove-orphans
for v in $(docker volume ls -q --filter="dangling=true"); do docker volume rm "$v"; done

# Restart demo
./scripts/start.sh

Pumba may be overloading the Docker inter-container network. Consider tweaking the Pumba settings in scripts/latency_docker.sh and re-test in your environment.

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README.md

README.md

Overview

Multi-region Architecture

Configurations

Broker

Client

Topic

Concepts

Run the Demo

Install the demo

Start Docker Compose

Inject latency and packet loss

Create Topics

Producer Testing

Consumer Testing

Monitoring Observers

Failover and Failback

Fail region west

Fail over observers

Failback region west

Run end-to-end demo

Stop demo

Troubleshooting

Files

README.md

Latest commit

History

README.md

File metadata and controls

Overview

Multi-region Architecture

Configurations

Broker

Client

Topic

Concepts

Run the Demo

Install the demo

Start Docker Compose

Inject latency and packet loss

Create Topics

Producer Testing

Consumer Testing

Monitoring Observers

Failover and Failback

Fail region west

Fail over observers

Failback region west

Run end-to-end demo

Stop demo

Troubleshooting