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. For local-container spaces, the selected server can still be changed while the space is stopped when the template allows node migration.

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 a local-container space has not started yet, you can reopen the edit form and change the selected server before the first start. After a space has been started, reassignment is only available for stopped spaces whose template explicitly allows node migration.

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