6.5. Configuring XDCR Using Load Balancers

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6.5. Configuring XDCR Using Load Balancers

Kubernetes load balancers are an alternative for making VoltDB clusters accessible outside the Kubernetes cluster or region they are in. In this case you are not using load balancers for their traditional role, balancing the load between multiple pods. Instead, the load balancers are solely used to provide externally accessible IP addresses.

There are two approaches to using load balancers. The first approach is to assign a load balancer for each node of the cluster. Since the nodes are externally reachable through persistent IP addresses on their corresponding load balancer, the load balancers can be used for both the network discovery and replication phases. The second approach is to use only one load balancer for the entire cluster to provide network discovery, and use virtual network peering, available from your hosting provider, for replication.

Many hosting platforms, such as Google Cloud or AWS, provide proprietary mechanisms for performing network peering between regions or data centers. Each of these solutions has its own unique set up and configuration, separate from the configuration of VoltDB and the VoltDB Operator . As a result, using a network peering service is not as simple as the use of load balancers for replication. However, they can be significantly more cost effective when paired with a single load balancer for network discovery.

There is also the choice of assigning the IP addresses for the load balancers dynamically, or having them selected from a range of static addresses. Dynamic assignment is simpler, since you do not need to arrange with your hosting provider for pre-assigned IPs or hostnames. However, dynamic addresses also mean you do not know what the addresses are until the cluster starts. This means the remote XDCR cluster cannot assign the source property until after the cluster starts with its associated load balancers and you can determine the IP addresses assigned to them.

6.5.1. Separate Load Balancers For Each Node (cluster.serviceSpec.perpod)

First you must assign the DR id and role as Helm properties. If the remote cluster is using static addresses, you can specify one of its nodes as the source, as in the following example. If you are using dynamic load balancers, leave the source property blank and use the helm upgrade --set command once the clusters are running to assign a resulting node address for the remote cluster.

cluster:
  config:
    deployment:
      dr:
        id: 1
        role: xdcr
        connection:
          enabled: true
          source: "chicago-dc-2"  # Remote cluster

Then in the cluster.serviceSpec section, you enable perpod by setting its type to LoadBalancer. You will also want to set the dr.enabled property to true so the per pod load balancers are used for network discovery as well as replication.

For dynamically assigned addresses, set the publicIPFromService to true:

cluster:
  serviceSpec:
    perpod:
      type: LoadBalancer
      publicIPFromService: true
      dr:
        enabled: true

For static IP addresses, use the staticIPs property to specify the addresses to assign when creating the load balancers and, again, set dr.enabled to true.

cluster:
  serviceSpec:
    perpod: 
      enabled: true
      type: LoadBalancer
      staticIPs:
      - 12.34.56.78
      - 12.34.56.79
      - 12.34.56.80
      dr:
        enabled: true

6.5.2. Single Load Balancer For Discovery with Virtual Networking Peering (cluster.serviceSpec.dr)

To reduce the number of resources needed to connect XDCR clusters in different regions, you can use a single load balancer for network discovery and use virtual network peering services from your hosting provider for connecting the two clusters during replication. How you set up and configure your network peering is specific to each provider. See your provider's documentation for additional information. This section describes how to set up a single Kubernetes load balancer for network discovery once you have your network peering established.

First you must assign the DR id and role as Helm properties and, if known in advance, the source for the remote cluster:

cluster:
  config:
    deployment:
      dr:
        id: 1
        role: xdcr
        connection:
          enabled: true
          source: "chicago-dc-2"  # Remote cluster

Then in the cluster.serviceSpec section, you enable the dr service (rather than perpod) and set its type to LoadBalancer. You may also need to provide additional annotations that help configure the service. These annotations are specific to the host environment you are using. So, for example, the following configuration provides annotations for AWS and the Google Cloud:

cluster:
  serviceSpec:
    dr: 
      enabled: true
      type: LoadBalancer
      annotations:
        # Google Cloud
        networking.gke.io/load-balancer-type: "Internal"
        networking.gke.io/internal-load-balancer-allow-global-access: "true"

        # AWS
        service.beta.kubernetes.io/aws-load-balancer-internal: "true"
        service.beta.kubernetes.io/aws-load-balancer-type: "nlb"