Node Selection

Node selection determines which server will host a space when multiple servers are available. Knot can automatically select the best server based on availability and runtime requirements, or you can manually specify a server during space creation.

Overview

When multiple servers are available, you can choose where a space is deployed:

• Automatic Selection (default): Knot selects the best available server
• Manual Selection: You choose a specific server when creating the space

If only one server can run the space, that server is automatically selected.

Automatic Selection

When creating a space, leave the server selection set to Auto to let Knot choose the best server.

Selection Criteria

Knot evaluates servers in the zone and selects based on the following priorities:

1. Runtime Requirements

   • If the template specifies a container runtime, only servers with that runtime are considered
   • If no runtime is specified, Knot uses the configured preference order (defaults to Docker, Podman, Apple Containers)

2. Zone Affinity (optional)

   • If configured, only servers in the same zone as the request are considered
   • Useful for geographic distribution or logical separation
   • See Multi-Server Setup for zone configuration

3. Load Balancing

   • The server with the lowest number of allocated spaces is selected
   • If servers have equal load, one is chosen at random

Runtime Detection and Configuration

Each server in the zone exposes which container runtimes it supports:

• Docker: Detected via docker info
• Podman: Detected via podman info
• Apple Containers: Detected via container system status

The runtime preference order is configured in your knot.toml configuration:

[server.local_containers]
  runtime_pref = ["podman", "apple"]

This defaults to ["docker", "podman", "apple"]. If a runtime isn’t listed, it won’t be used.

Each server in the zone exposes which container runtimes it supports:

• Docker: Detected via docker info
• Podman: Detected via podman info
• Apple Containers: Detected via container system status

Knot automatically detects available runtimes on each server.

Only servers capable of running the space’s required runtime are shown as options when creating a space.

Manual Selection

To manually select a server for your space:

1. Navigate to the space creation dialog
2. In the server selection dropdown, choose a specific server instead of Auto
3. Complete the space creation as normal

When to Use Manual Selection

• You need to place a space on a server with specific resources
• You’re testing deployment on a particular server
• You have affinity requirements (e.g., database and application on the same server)
• A server has specialized hardware or configurations

Cluster Considerations

In a multi-server cluster:

• Server load information is updated in real-time
• Automatic selection ensures even distribution across available servers

For high availability, consider:

• Distributing spaces across multiple servers
• Using manual selection for critical services
• Monitoring server resource utilization

Troubleshooting

No Servers Available

If no servers appear in the selection dropdown:

• Verify servers are online and part of the cluster
• Check that the required container runtime is available on at least one server

Server Not Listed

If an expected server doesn’t appear:

• Confirm the server is part of the zone (check logs)
• Verify the container runtime matches the template requirements
• Check the server’s connectivity and agent status

Wrong Server Selected

If automatic selection chooses an unexpected server:

• Review the runtime preference order in knot.toml
• Check current space allocation across servers