Node Selection

Node selection determines which server in the zone will host a space. 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 in a zone, 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 in the zone 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: Docker > Podman > Apple Containers

2. Zone Affinity

   • Only servers in the same zone as the request are considered for local containers (Docker, Podman, Apple Containers)
   • Nomad deployments are handled separately by the Nomad scheduler

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 defined in your knot.toml configuration:

[server.docker]
  host = "unix:///var/run/docker.sock"

[server.podman]
  host = "unix:///var/run/podman.sock"

Knot automatically detects available runtimes. The preference order is:

1. Docker
2. Podman
3. Apple Containers (macOS only)

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

Node Affinity

Spaces can be configured with node affinity for persistent placement:

• Automatic (default): No specific server preference; Knot chooses based on current load
• Manual: Space is assigned to a specific server and will prefer that server on restart

Node affinity is stored with the space configuration and persists across space restarts.

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 in the same zone
• Check that the required container runtime is available on at least one server
• Ensure your user has permissions to create spaces on the servers

Server Not Listed

If an expected server doesn’t appear:

• Confirm the server is in the same zone
• 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
• Use manual selection to override automatic behavior