About Connection Load Balancing Policies

Connection load balancing policies help spread the load of servicing client connections by redirecting connections based on the connection's origin. A load balancing policy consists of:

  • Network addresses that identify particular IP address and port number combinations on a node.
  • One or more connection load balancing groups that consists of network addresses that you want to handle client connections. You define load balancing groups using fault groups, subclusters, or a list of network addresses.
  • One or more routing rules that map a range of client IP addresses to a connection load balancing group.

When a client connects to a node in the database with load balancing enabled, the node evaluates all of the routing rules based on the client's IP address to determine if any match. If more than one rule matches the IP address, the node applies the most specific rule (the one that affects the least number of IP addresses).

If the node finds a matching rule, it uses the rule to determine the pool of potential nodes to handle the client connection. When evaluating potential target nodes, it always ensures that the nodes are currently up. The initially-contacted node then chooses one of the nodes in the group based on the group's distribution scheme. This scheme can be either choosing a node at random, or choosing a node in a rotating "round-robin" order. For example, in a three-node cluster, the round robin order would be node 1, then node 2, then node 3, and then back to node 1 again.

After it processes the rules, if the node determines that another node should handle the client's connection, it tells the client which node it has chosen. The client disconnects from the initial node, and then connects to the chosen node and continues with the connection process (either negotiating encryption if the connection has TLS/SSL enabled, or authentication).

If the initial node chooses itself based on the routing rules, it tells the client to proceed to the next step of the connection process.

If no routing rule matches the incoming IP address, the node checks to see if classic connection load balancing is enabled by both Vertica and the client. If so, it handles the connection according to the classic load balancing policy. See Classic Connection Load Balancing for more information.

If no routing rule matches the incoming IP address and classic load balancing is not enabled, the node handles the connection itself. It also handles the connection itself if it cannot follow the load balancing rule. For example, if all nodes in the load balancing group targeted by the rule are down, then the initially-contacted node handles the client connection itself. In this case, the node does not attempt to apply any other less-restrictive load balancing rules that would apply to the incoming connection. It only attempts to apply a single load balancing rule.

Connection Load Balancing Policy Use Cases

Using load balancing policies you can:

  • Ensure connections originating from inside or outside of your internal network are directed to a valid IP address for the client. For example, suppose your Vertica nodes have two IP addresses: one for the external network and another for the internal network. These networks are mutually exclusive. You cannot reach the private network from the public, and you cannot reach the public network from the private. Your load balancing rules need to provide the client with an IP address they can actually reach.

  • Enable access to multiple nodes of a Vertica cluster that are behind a NAT router. A NAT router is accessible from the outside network via a single IP address. Systems within the NAT router's private network can be accessed on this single IP address using different port numbers. You can create a load balancing policy that redirects a client connection to the NAT's IP address but with a different port number.

  • Designate sets of nodes to service client connections from an IP address range. For example, if your ETL systems have a set range of IP addresses, you could limit their client connections to an arbitrary set of Vertica nodes, a subcluster, or a fault group. This technique lets you isolate the overhead of servicing client connections to a few nodes. It is useful when you are using subclusters in an Eon Mode database to isolate workloads (see Subclusters for more information).

Using Connection Load Balancing Policies With IPv4 and IPv6

Connection load balancing policies work with both IPv4 and IPv6. As far as the load balancing policies are concerned, the two protocols represent separate networks. If you want your load balancing policy to handle both IPv4 and IPv6 addresses, you must create separate sets of network addresses, load balancing groups, and rules for each protocol. When a client opens a connection to a node in the cluster, the addressing protocol it uses determines which set of rules Vertica consults when deciding whether and how to balance the connection.

The Differences Between Connection Load Balancing Policies and Classic Connection Load Balancing

There several differences between the classic load balancing feature and the load balancing policy feature:

  • In classic connection load balancing, you just enable the load balancing option on both client and server, and load balancing is enabled. There are more steps to implement load balancing policies: you have to create addresses, groups, and rules and then enable load balancing on the client.
  • Classic connection load balancing only supports a single, cluster-wide policy for redirecting connections. With connection load balancing policies, you get to choose which nodes handle client connections based on the connection's origin. This gives you more flexibility to handle complex situations. Examples include routing connections through a NAT-based router or having nodes that are accessible via multiple IP addresses on different networks.
  • In classic connection load balancing, each node in the cluster can only be reached via a single IP address. This address is set in the EXPORT_ADDRESS column of the NODES system table. With connection load balancing policies, you can create a network address for each IP address associated with a node. Then you create rules that redirect to those addresses.

Overview of Creating a Load Balancing Policy

There are three steps you must follow to create a load balancing policy:

  1. Create one or more network addresses for each node that you want to participate in the connection load balancing policies.
  2. Create one or more load balancing groups to be the target of the routing rules. Load balancing groups can target a collection of specific network addresses. Alternatively, you can create a group from a fault group or subcluster. You can limit the members of the load balance group to a subset of the fault group or subcluster using an IP address filter.
  3. Create one or more routing rules.

While not absolutely necessary, it is always a good idea to idea to test your load balancing policy to ensure it works the way you expect it to.

After following these steps, Vertica will apply the load balancing policies to client connections that opt into connection load balancing. See Enabling Native Connection Load Balancing in ADO.NET, Enabling Native Connection Load Balancing in JDBC, and Enabling Native Connection Load Balancing in ODBC, for information on enabling load balancing on the client. For vsql, use the -C command-line option to enable load balancing.

These steps are explained in the other topics in this section.

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