When reading a GBase Database(GBase 8c) deployment configuration for the first time, engineers often encounter the same question:

Why does one database instance need both host and agent_host?

The answer is network traffic separation.

These two fields serve different communication purposes in the GBase Database cluster. Understanding the distinction is essential when planning dual-NIC deployments, configuring network subnets, and troubleshooting cluster heartbeat timeouts.

1. host: The Data-Plane Address

host is the data-plane address used for communication between database instances.

Typical communication paths include:

  • CN-to-DN communication
  • DN primary-to-standby replication
  • GTM communication with other database instances

This network carries database-related traffic. Depending on the workload, traffic volume can be substantial and bursty.

For this reason, the deployment manual recommends using a 10GbE network for host in a dual-NIC configuration.

2. agent_host: The Control-Plane Address

agent_host serves a different purpose.

It is the control-plane address used for communication with management components such as:

  • gha_server
  • DCS

This network carries management commands, heartbeat messages, and other cluster coordination traffic.

Unlike bulk database traffic, control-plane traffic is relatively small but sensitive to latency and communication interruptions.

The documented dual-NIC configuration uses a 1GbE network for agent_host.

3. Why Separate the Two Network Planes?

The reason is not simply bandwidth. It is network traffic isolation.

Consider a cluster where database traffic and management traffic share one network interface.

During functional testing, the workload is usually light enough that both types of communication work normally.

Under heavy workloads, however, large queries and bulk scans can compete for network resources with control-plane heartbeats.

The resulting sequence can look like this:

  1. Bulk database traffic increases network utilization.
  2. Control-plane heartbeat latency increases.
  3. Heartbeat communication encounters timeouts.
  4. Cluster health assessment and failover behavior may become unstable.

This is why a network configuration that appears perfectly functional during initial acceptance testing can become problematic under sustained load.

For GBase Database high-availability deployments, separating data-plane and control-plane traffic helps reduce this resource contention.

4. The Subnet Constraint Matters Too

The network design is not only about assigning two different IP addresses.

The deployment manual also specifies a subnet relationship:

  • agent_host shares a subnet with gha_server and DCS.
  • host uses its own subnet.

This distinction matters when planning IP addresses, routing, firewall rules, and network interfaces.

Simply configuring two IP addresses does not guarantee proper network isolation if both communication paths still share the same network segment and physical resources.

5. Can Both Fields Use the Same IP Address?

Yes, in a single-NIC deployment, both fields can use the same address when permitted by the deployment configuration.

For example, functional testing may succeed with:

host: 192.168.10.101 agent_host: 192.168.10.101

But this configuration does not provide the network isolation of a dual-NIC architecture.

Under heavy workloads, database traffic and management traffic still compete for the same network resources.

The important distinction is that successful connectivity does not necessarily demonstrate sufficient network isolation under production load.

6. A11: A Pre-Installation Check Worth Watching

There is also a configuration-level detail worth remembering.

In the documented GBase Database pre-installation checks, A11 can identify anomalies related to the host and agent_host network configuration.

If A11 reports an abnormal result, do not look only at the physical NICs.

Also review:

  • Whether host and agent_host are assigned to the intended network interfaces
  • Whether the IP addresses belong to the expected subnets
  • Whether agent_host has the required connectivity to gha_server and DCS
  • Whether the configured network arrangement matches the deployment design

This is useful because some network configuration problems can be identified before the actual installation begins.

7. A Real Deployment Lesson

Consider a three-host GBase Database deployment with dual NICs.

Both host and agent_host were initially configured using the business network subnet.

Functional testing passed without obvious problems.

However, when the workload reached approximately 80% of the tested load, intermittent failover switching began. The logs showed heartbeat timeouts.

After correcting agent_host to use the management subnet and reinstalling the cluster, the problem disappeared.

The important lesson is not that every single-NIC configuration will fail under load. It is that functional connectivity alone cannot prove that a network architecture provides adequate traffic isolation.

Two configuration fields can determine whether the data plane and control plane remain independent under pressure.

8. An Easy Way to Remember the Difference

My mnemonic is simple:

  • host: The address used for database instance-to-instance communication.
  • agent_host: The address used by management components to communicate with the database cluster.

GBase Database separates these two network planes to reduce interference between database workloads and cluster management traffic.

Using the same address for both may be valid in a single-NIC deployment, but it deliberately gives up that separation.

Two fields, two traffic planes, two different responsibilities.

When designing a GBase Database(GBase 8c) cluster, network isolation should be considered before installation, not after the first heartbeat timeout.