Multi-Region Deployment of Confluent Platform in Confluent for Kubernetes

Confluent for Kubernetes (CFK) supports configuring, deploying, and operating Confluent Platform in multi-region clusters (MRCs). In the MRC deployment scenario, Kafka, ZooKeeper, and Schema Registry are deployed in multiple regions to form a logical cluster stretched across Kubernetes regions.

For information about Confluent Platform in multi-region clusters, see Multi-Region Clusters.

To form a multi-region cluster, Confluent must be deployed across three or more Kubernetes clusters.

CFK supports various multi-region cluster deployment scenarios for Confluent Platform. The following are example deployment scenarios.

  • A multi-region cluster deployment across three Kubernetes regions, where each cluster hosts CFK, Kafka brokers, and ZooKeeper servers:

    _images/co-mrc-3clusters.png

  • A multi-region cluster deployment across three Kubernetes regions, where each cluster hosts CFK, ZooKeeper servers, and two clusters host Kafka brokers:

    _images/co-mrc-2.5clusters.png

You can set up an MRC with the following communication methods among ZooKeeper, Kafka, and Schema Registry deployed across regions:

  • Use internal listeners among ZooKeeper, Kafka, and Schema Registry across regions.

    You set up a DNS resolution that allows each region in the MRC configuration to be able to resolve internal pods in other regions. Internal listeners are used among the MRC components (ZooKeeper, Kafka, and Schema Registry).

  • Use external access among ZooKeeper, Kafka, and Schema Registry across regions.

    Without the required networking configuration, CFK redirects internal communication among the MRC components (ZooKeeper, Kafka, and Schema Registry) to use endpoints that can be accessed externally by each region.

    For MRC, if there are other components that depend on Kafka, you need to configure an external listener for Kafka. If you want to reduce the number of load balancers, you can use an alternative way for external access, such as Ingress.

The supported security features work in multi-region cluster deployments. For specific configurations, see Configure Security with Confluent for Kubernetes.

Setup requirements for Kubernetes clusters

Namespace naming
Have one uniquely named namespace in each Kubernetes region cluster.
Flat pod networking among Kubernetes region clusters (when using internal listeners)
Pod Classless Inter-Domain Routings (CIDRs) across the Kubernetes clusters must not overlap.
DNS resolution among Kubernetes region clusters (when using internal listeners)

Kubernetes clusters must be able to resolve other’s internal DNS and route to other’s internal pods.

You can use kube-dns or CoreDNS to expose region clusters’ DNS.

Firewall rules (when using internal listeners)

Allow TCP traffic on the standard ZooKeeper, Kafka, and Schema Registry ports among all regions

clusters’ pod subnetworks.

For specific configuration and validation steps on various platforms, specifically, GKE, EKS, and AKS, see Multi-region Cluster Networking in the CFK example repo.

Kubernetes region node label

Kubernetes nodes in each region have labels defined as topology.kubernetes.io/region=<region>.

For example, when using three Kubernetes clusters, us-central-1, us-east-1, and us-west-1, the nodes in the regions will have labels topology.kubernetes.io/region=us-central-1, topology.kubernetes.io/region=us-east-1, and topology.kubernetes.io/region=us-west-1, respectively.

When CFK in each region schedules a broker pod, it will look up the region by reading the topology.kubernetes.io/region label of the Kubernetes node in the cluster, and deploy the broker to these nodes that have the matching broker.rack=<region>. You should not override the broker.rack property. For more information about the property, see broker.rack property.

Kubernetes context

When working with multiple Kubernetes clusters, the kubectl commands run against a cluster in a specific context that specifies a Kubernetes cluster, a user, and a namespace.

Append --context <cluster-context> to the kubectl commands to ensure they are run against the correct cluster.

For sample use case scenarios, see Confluent for Kubernetes examples GitHub repo.

Configure Confluent Platform in a multi-region cluster

Using distinct Kafka broker IDs, ZooKeeper IDs, and Schema Registry IDs, CFK creates and manages a logical multi-region cluster of each component.

  1. Deploy CFK to each region.

  2. Configure MRC Zookeeper.

    For Kafka to communicate with ZooKeeper using an external endpoint within the MRC region, enable the Zookeeper MRC external listener. ZooKeeper MRC external listeners support load balancers and node ports.

  3. Configure MRC Kafka.

    For Kafka brokers to communicate with other Kafka brokers using an external endpoint within the MRC region, enable the Kafka MRC external listener. Kafka MRC external listeners support load balancers, node ports, routes, port-based and hosted-based static accesses.

    Note that the MDS listener does not currently support routes for external access.

  4. Configure MRC Schema Registry, or configure active-passive MRC Schema Registery.

    For Kafka to communicate with the active-passive Schema Registry clusters using an external endpoint within the MRC region, enable the Schema Registry MRC external listener. Schema Registry MRC external listeners support load balancers.

  5. Configure the remaining Confluent Platform components, including Control Center, Connect, and ksqlDB, to be deployed in one Kubernetes region cluster and to utilize the stretched Kafka.

    In the component CRs, specify a comma-separated list of Kafka endpoints.

    For example, for Confluent Platform components to use internal listeners to access Kafka:

    kind: <Confluent component>
spec:
  dependencies:
    kafka:
      bootstrapEndpoint: kafka.central.svc.cluster.local:9071,kafka.east.svc.cluster.local:9071,kafka.west.svc.cluster.local:9071

    For example, for Confluent Platform components to use external URLs to access Kafka:

    kind: <Confluent component>
spec:
  dependencies:
    kafka:
      bootstrapEndpoint: kafka.central.svc.cluster.local:9071,kafka-east.platformops.dev.gcp.devel.cpdev.cloud:9092,kafka-west.platformops.dev.gcp.devel.cpdev.cloud:9092

  6. Apply the CRs with the kubectl apply -f <component CRs> in each region.

Configure ZooKeeper in MRC

To form a logical cluster of ZooKeeper across Kubernetes region clusters:

  1. Set the ZooKeeper server id offset to a different number in each Kubernetes region cluster using annotations in the ZooKeeper CR.

    For example:

    kind: Zookeeper
metadata:
  annotations:
    platform.confluent.io/zookeeper-myid-offset: "100"

    The default is "0".

    The offsets should be sufficiently spread out among regions, like 100, 200, 300, etc., to accommodate future cluster growth in each region.

    Because this offset cannot be changed once set, carefully consider how wide you want these offsets to be before you deploy the clusters.

  2. Specify the peer ZooKeeper servers in the spec.peers property of the ZooKeeper CR.

    For example:

    kind: Zookeeper
spec:
  peers:
    - server.100=zookeeper-0.zookeeper.central.svc.cluster.local:2888:3888
    - server.200=zookeeper-0.zookeeper.east.svc.cluster.local:2888:3888
    - server.300=zookeeper-0.zookeeper.west.svc.cluster.local:2888:3888

Configure ZooKeeper in MRC with external access URLs

You can use a load balancer or node ports for ZooKeeper external access.

To configure ZooKeeper to use the external access URL to communicate with the other ZooKeeper and Kafka in MRC:

  1. In each ZooKeeper CR, specify the peer ZooKeeper URLs (spec.peers), using external access URLs to other regions but a local URL to its own region. ZooKeeper instances communicate with one another through ports 2888 (peer) and 3888 (leader election).

    For example:

    kind: Zookeeper
spec:
  peers:
    - server.0=zookeeper-0.zookeeper.central.svc.cluster.local:2888:3888
    - server.10=zk-east0.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.11=zk-east1.platformops.dev.gcp.devel.cpdev.cloud:2888:3888

  2. Configure the external MRC listener:

    kind: Zookeeper
  spec:
    externalAccess:
      type:             --- [1]
      loadBalancer:     --- [2]
        prefix:         --- [3]
        domain:         --- [4]
      nodePort:         --- [5]
        host:           --- [6]
        nodePortOffset: --- [7]
    • [1] Required. The valid values are loadBalancer and nodePort.
    • [2] Configure the external access through load balancers.
    • [3] ZooKeeper prefix.
    • [4] Required. Set it to the domain where your Kubernetes cluster is running.
    • [5] Configure the external access through node ports.
    • [6] The host name.
    • [7] The starting port number.

Configure Kafka in MRC

To form a logical cluster of Kafka across Kubernetes region clusters:

  1. Set the broker id offset to a different number in the Kafka CR in each region.

    For example:

    kind: Kafka
metadata:
  annotations:
    platform.confluent.io/broker-id-offset: "100"

    The default is "0".

    The offsets should be sufficiently spread out among regions, like 100, 200, 300, etc., to accommodate future cluster growth in each region.

    This offset cannot be changed once set. So, you should carefully consider how wide you want these offsets to be before you deploy the clusters.

  2. In the Kafka CRs, specify a comma-separated list of ZooKeeper endpoints in spec.dependencies.zookeeper.endpoint in the ZooKeeper CR. This value should be the same in all Kafka CRs across Kubernetes clusters.

    Kafka communicates with ZooKeeper through the client port (2181/2182).

    For example:

    kind: Kafka
spec:
  dependencies:
    zookeeper:
      endpoint: zookeeper.central.svc.cluster.local:2182/mrc,zookeeper.east.svc.cluster.local:2182/mrc,zookeeper.west.svc.cluster.local:2182/mrc

    The ZooKeeper node id (mrc in the above example) can be any string, but it needs to be the same for all the Kafka deployments in a multi-region cluster.

    If you are deploying multiple multi-region clusters utilizing the same ZooKeeper, use different node ids, for example, mrc1, mrc2, etc., in each multi-region cluster.

    This value should not be changed once the cluster is created. Otherwise, it results in data loss.

Configure Kafka in MRC with external access URLs

When defined with external access, inter-broker communications go across external access on the replication listener.

The replication listener supports all the external access methods that Kafka supports, namely a load balancer, node ports, routes, port-based and hosted-based static accesses.

In the Kafka CR in each region, configure inter-broker external access to Kafka brokers through the replication listener:

kind: Kafka
spec:
  listeners:
    replication:
      externalAccess:
        type:                      --- [1]
        loadBalancer:              --- [2]
          bootstrapPrefix:         --- [3]
          brokerPrefix:            --- [4]
          domain:                  --- [5]
        nodePort:                  --- [6]
          host:                    --- [7]
          nodePortOffset:          --- [8]
        route:                     --- [9]
          bootstrapPrefix:         --- [10]
          brokerPrefix:            --- [11]
          domain:                  --- [12]
        staticForHostBasedRouting: --- [13]
          domain:                  --- [14]
          port:                    --- [15]
          brokerPrefix:            --- [16]
        staticForPortBasedRouting: --- [17]
          host:                    --- [18]
          portOffset:              --- [19]
      internal:
        tls:
          enabled: true            --- [20]

  • [1] Required. Specify the Kubernetes service for external access. The valid options are loadBalancer, nodePort, route, staticForPortBasedRouting, and staticForHostBasedRouting.

  • [2] Configure the external access through load balancers.

  • [6] Configure the external access through node ports.

  • [9] Configure the external access through OpenShift routes.

    To use routes, TLS must be enabled ([20]) on the internal listener.

  • [13] Configure the external access through host-based static routing.

  • [17] Configure the external access through port-based static routing.

  • [3] [10] Kafka bootstrap prefix.

  • [4] [11] [16] Kafka broker prefix.

  • [5] [12] [14] Required. Set it to the domain where your Kubernetes cluster is running.

  • [7] [18] The host name to be used in the advertised listener for a broker.

  • [15] The port to be used in the advertised listener for a broker.

  • [8] [19] The starting port number.

  • [20] Required when the external access type is set to route ([1]).

RBAC in MRC with external access

When RBAC is enabled, CFK creates external access on the same service for both the replication and token listeners. The kafka.spec.listeners.replication.externalAccess settings are used to create a token listener with the following exceptions:

  • Route

    Separate routes will be created for the replication listeners and the token listeners. The token listener uses the [brokerPrefix]-token[replica].[domain] domain, and the replication listener uses the [brokerPrefix][replica].[domain] domain.

    For example, if the domain is example.com and the brokerPrefix is default b, the replication listener domains will be b0.example.com, b1.example.com, b2.example.com, and so on. The token listener domains will be b-token0.example.com, b-token1.example.com, b-token2.example.com.

  • StaticForHostBasedRouting

    The token listener uses the [brokerPrefix]-token[replica].[domain] domain, and the replication listener uses the [brokerPrefix][replica].[domain] domain.

For examples, see External Access in MRC.

Configure Schema Registry in MRC

Currently, the Schema Registry clusters in the stretch (non active-passive) mode only work

with internal listeners.

To form a logical cluster of Schema Registry across Kubernetes region clusters, specify the following properties in each Schema Registry CR:

kind: SchemaRegistry
spec:
  configOverrides
    server:
      - schema.registry.group.id --- [1]
      - kafkastore.topic         --- [2]
  dependencies:
    kafka:
      bootstrapEndpoint:         --- [3]
  • [1] Specify the same group id for all Schema Registry services across all Kubernetes region clusters.
  • [2] Specify a string that starts with _ for this log topic name. Use the same value for all Schema Registry services across all Kubernetes region clusters.
  • [3] Specify a comma-separated list of Kafka endpoints across all Kubernetes region clusters.

The following is an example snippet of a Schema Registry CR:

kind: SchemaRegistry
spec:
  dependencies:
    kafka:
      bootstrapEndpoint: kafka-central.platformops.dev.gcp.devel.cpdev.cloud:9092,kafka-west.platformops.dev.gcp.devel.cpdev.cloud:9092,kafka-east.platformops.dev.gcp.devel.cpdev.cloud:9092
  configOverrides:
    server:
      - schema.registry.group.id=schema-registry-mrc
      - kafkastore.topic=_schemas_mrc

For details about deploying a multi-region Schema Registry, see Multi Data Center Setup of Schema Registry.

Configure active-passive Schema Registry in MRC

Communication among Schema Registry clusters in different regions is necessary in the active-passive mode. In the active-passive mode, data is copied from the follower Schema Registry to the leader Schema Registry. The follower Schema Registry needs to be able to resolve the leader’s endpoint.

To form a logical cluster of active-passive Schema Registry across Kubernetes region clusters, specify the following properties in each Schema Registry CR:

kind: SchemaRegistry
spec:
  configOverride:
    server:
      - schema.registry.group.id              --- [1]
      - leader.eligibility                    --- [2]
  • [1] Specify the same group id for all Schema Registry services across all Kubernetes region clusters.
  • [2] Set to false on the passive clusters, and true on the active clusters.

Configure active-passive Schema Registry in MRC with external access

Currently, in CFK, active-passive schema registry is only supported through load balancers.

To set up Schema Registry clusters in the active-passive mode with external MRC access, conigure each Schema Registry CR as below:

kind: SchemaRegistry
spec:
  configOverride:
    server:
      - inter.instance.listener.name=EXTERNAL --- [1]
      - schema.registry.group.id              --- [2]
      - leader.eligibility                    --- [3]
  listeners:
    external:
      externalAccess:
        type: loadbalancer                    --- [4]
        loadBalancer:                         --- [5]
          prefix:                             --- [6]
          domain:                             --- [7]
  • [1] Required.
  • [2] Specify the same group id for all Schema Registry services across all Kubernetes region clusters.
  • [3] Set to false on the passive clusters, and true on the active clusters.
  • [4] Required. Set to loadBalancer.
  • [5] Configure the external access through load balancers.
  • [6] Schema Registry prefix.
  • [7] Required. Set it to the domain where your Kubernetes cluster is running.

Manage Confluent Platform in the multi-region cluster

The following are a few of the common tasks you would perform in a multi-region cluster. Some can be done in one region and get propagated to all regions, and some can be done in a specific region as noted.

Create topics

You can create and manage topics in any region in a multi-region cluster, and those topics are accessible from all the regions in the cluster.

See Manage Kafka Topics for creating and managing topics.

Scale Kafka

You need to scale Kafka at the regional level. Update the Kafka CR in a specific region to scale the Kafka cluster in that region.

See Scale Confluent Platform Clusters and Balance Data using Confluent for Kubernetes for scaling Kafka clusters.

Manage rolebindings

You can create and manage rolebindings in any region in a multi-region cluster, and those rolebindings are accessible from all the regions in the cluster.

See Manage Confluent Role-based Access Control using Confluent for Kubernetes.

Rotate certificates
To rotate TLS certificates used in a region, you follow the steps described in Manage TLS Certificates in Confluent for Kubernetes in the specific region.
Restart Kafka
You need to restart Kafka in a specific region as described in Restart Confluent Platform using Confluent for Kubernetes.

Troubleshoot MRC deployment issues

Issue: ZooKeeper does not start up

ZooKeeper experiences problems forming a quorum. The quorum may form, but some peers never join it, or the quorum may never form. The quorum may form, but ZooKeeper logs show ongoing communication issues.

The ZooKeeper logs contain an error message like the following:

[INFO] 2023-07-26 03:15:56,165 [QuorumConnectionThread-[myid=20]-9]
org.apache.zookeeper.server.quorum.QuorumCnxManager startConnection - Have
smaller server identifier, so dropping the connection: (myId:20 --> sid:30)

And, soon after in the log of the ZooKeeper node with ID 30:

[WARN] 2023-07-26 03:16:01,171 [QuorumConnectionThread-[myid=30]-10]
org.apache.zookeeper.server.quorum.QuorumCnxManager initiateConnection -
Cannot open channel to 20 at election address /172.31.16.90:3888
java.net.SocketTimeoutException: connect timed out

Cause: When forming a quorum, ZooKeeper servers will communicate their IP address to other members of the quorum, which triggers the other members to contact them on that IP address if they do not already have a connection. In an environment where the ensemble is spread across multiple Kubernetes clusters, the name and IP address a host uses inside the Kubernetes cluster may be different from the ExternalIP of the Kubernetes Service used by connections originating from outside the cluster, and the DNS name used to resolve that Kubernetes Service.

Solution: Configure the ZooKeeper peer list so that the hostname each server looks up for its own ZooKeeper ID is 0.0.0.0. This prevents each peer from communicating its IP address to other peers, forcing each peer to communicate with other peers using the hostnames they have been configured with. This means that each ZooKeeper pod needs a unique peer list, which in turn means that the spec.replicas value for each ZooKeeper CR must be set to 1.

Take the following steps to configure ZooKeeper:

  1. On sites where multiple ZooKeeper nodes are required, create multiple ZooKeeper CRs.
  2. Set spec.replicas to 1 in each ZooKeeper CR.
  3. Set the ZooKeeper pod’s own hostname as 0.0.0.0.
  4. Configure appropriate Kubernetes Services and DNS records to allow clients and servers outside the Kubernetes cluster to communicate with the ZooKeeper pods within the cluster.

In the following example, the West region has two ZooKeeper CRs for two ZooKeeper pods:

apiVersion: platform.confluent.io/v1beta1
kind: Zookeeper
metadata:
  annotations:
    platform.confluent.io/zookeeper-myid-offset: "20"
  name: zookeeper20
  namespace: west
spec:
  peers:
    - server.30=zk-central0.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.10=zk-east0.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.11=zk-east1.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.20=0.0.0.0:2888:3888
    - server.21=zookeeper21-0.zookeeper21.west.svc.cluster.local:2888:3888
  replicas: 1
---
apiVersion: platform.confluent.io/v1beta1
kind: Zookeeper
metadata:
  annotations:
    platform.confluent.io/zookeeper-myid-offset: "21"
  name: zookeeper21
  namespace: west
spec:
  peers:
    - server.30=zk-central0.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.10=zk-east0.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.11=zk-east1.platformops.dev.gcp.devel.cpdev.cloud:2888:3888
    - server.20=zookeeper20-0.zookeeper20.west.svc.cluster.local:2888:3888
    - server.21=0.0.0.0:2888:3888
  replicas: 1